BIOCHEMISTRY OF SKIN BIOCHEMIE KUZE

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BIOCHEMISTRY OF SKIN BIOCHEMIE KUZE

• Prof. Dr. V. Pelouch, CSc.

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Kue

• Krome textu v anglictine - tento soubor -
  má ná student k disposici ceský text dve
  kapitoly ve skriptech
• Doplnky k biochemii III - Biochemie kue
• Úvod k biochemii II - Biochemie potu
• nekolik ceských textu razených na konci
  tohoto souboru

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SKIN

• Structure multilayer organ produced several
  specialized derivative structure - appendages
  (hair follicles, sweat and sebaceous glands
• a) ecrine glands secretion - but cell
  persisted as intact,
• b) appocrine glands secretion - but releasing
  part of cells into secret sweat glands
  connected with hair follicles
• Three layers
• a) epidermis, b) dermis, c) hypodermis

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FUNCTION I

• Many different functions
• Protection (skin has both mechanical protection
  organs and against UV beams - sun irradiation,
  then barriers against different chemical
  components or bacteria's due to low pH -
  4,5 -6,0 result of high lactate - see
  metabolism of skin),
• secretion sweat, sebum,
• immune reactions (Langerhans cells - reactions
  against infection ? pathway via haptens and
  soluble antigens to T lymphocytes another
  mechanisms moi-sture, low pH),

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FUNCTION II

• Thermoregulation (cholinergic innervations, in
  indifferent temperature tonus -
  vasoconstrictions only 500 ml/min of blood
• the change of temperature induced ? openning of
  arteriovenous anastomosis (subpapilary venous
  plexus is blood depo capacity 1500 ml
• Perception analysators for tactile and
  heat impulses

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Composition I

• EPIDERMIS
• cells - keratinocytes - derived from ectoderm
  
• Biochemistry epidermal cells are formed from a)
  keratin filament polypeptides (8-10 nm), b)
  microfilaments and c) microtubules (different
  ECM proteins some of them ? lipid component)
• Keratin polypeptides
• 30 different polypeptides (m.w. 40 -70
  kDa)
• - type I K10 - K20 domination
  of acid AA
• - type II K 1 - K 9
  domination either basic
• 
  or neutral AA
• High amount of sulphur - 2 , even
  5 hair
• abnormal keratin expression - molecular
  basis for skin
• 
  diseases

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Biochemistry of keratin in hair

• Hair keratin is elongated a helix with somewhat
  thicker domains near C- and N termini, pair of
  these helices are interwound to form two chain
  coiled coil ? protofilament ? protofibrils
• Wawing - why ?
• a) a - keratin exposed to moist heat can be
  stretched into ß - conformation but
  cooling revert to a confor-mation
• b) -S- S- cross- linkage reducing agent
  cleaves each cystine (-S- S-) into two
  cysteins (-SH) one on each adjacent chain.
  Moist heat breaks -H bonds and causes a helix
  to uncoil and stretch. After a time reducing
  agent is add ? new -S-S- bridges of adjacent
  chain, but not the same before the treatment.

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Biochemistry of keratin in nail

• Nail keratins are main organic components
  - surrounded by globular matrix proteins
• organic material has high concentration of
  both proline (important for structure) and
  cystine (disulfide bonds),
• organic trace elements are from AA - sulfur and
  nitrogen
• Inorganic components water (10-30), trace
  elements,

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Keratin effect of heat on remodela-tion of
fibril structures wawing
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Composition II

• Ad a) EPIDERMIS
• Morphology keratinization from live cell in
  epidermis - series of morphological and
  metabolic events - finally ? corneocyt - to
  dead cell
• Loss of ability to proliferate
• Increase in cell size and cell flattering
• Remodelation of cell organelles both lost and
  new formation
• Synthesis of new proteins and lipids
• Changes in plasma membrane properties, cell
  surface antigens and receptors
• Dehydratation
• finally - corneocyt - dead cell

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Composition III

• Ad a) EPIDERMIS
• Biochemistry proteins (keratins, ECM
  proteins and protein with associated lipids)
  are regulated
• by
• growth factors - acting via different receptors
  from birth ? death (EGF - epidermal growth
  factors, TGF - transformic g.f., cytokines,
  steroid substances)
• under effect of
• Receptors steroid/thyroid super family
  (retinoids, vitamin D), important role of Ca -
  ions (e.g. for differentiation)
• Metabolism glucose ? glycolysis (80) ? lactate
• (20 by PPP cycle ? production of NADPH)
  further-more glutamine ? glutamate

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Composition IV

• Ad a) EPIDERMIS
• other cells - melanocytes (arise from neural
  ectoderm of neural tube) ? melanosome
  distinctive organelle of melanocytes (both
  melanocytes and melanosome dendrites contain
  actin and microtubules) ? pigments ?eumelanin,
  feomelanin (their distribution varies with
  races)
• stimulation UV light and by MSH (melanine
  stimulation hormone - produced by
  keratinocytes) melanosomes are transferred into
  keranocytes (by fusion and break-down by PL of
  both, then exocytose of melanosome from
  melanocyte followed by endocytosis into
  kera-tocyte ? protrusion of melanocyte dendrite
  into kerati-nocyte
• entry of melanocytes into embryonic skin occurs
  early in fetal development (50 days of
  gestation age)

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Composition V

• Ad a) EPIDERMIS
• melanosomes ? specific melanin units ?
  pigments (eumelanin and feomelanin) are
  synthetized from tyrosine
• Biochemistry tyrosine ? hydroxylation by DOPA
  (3,4 dihydroxyphenyl -alanine ? next oxidation
  ? dopachinon (both steps needs enzyme
  tyrosinase exhibited two activities a)
  tyrosin-hydroxylation,
• b)
  DOPA oxidation)
• ? polymerization of dopachinon ?
  eumelanin
• ? polymerization of dopachinon with
  cystein ?
• 
  precursor of feomelanins

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Formation of eumelanis and feomelanins from
tyrosin
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Composition VI

• Ad a) EPIDERMIS
• cells - Langerhans cells
• Dendritic cells (occupied 2 -8 of epidermis)
  resided in suprabasal layer - attracted to
  keranocytes by E- cathe-rin receptor (there are
  in other squamous epithelia oral cavity,
  esophagus, vagina too, in lymphoid organs
  spleen, thymus and lymph node) - these cells
  arise from bone marrow early in embryonic
  development, reside in epidermis for time their
  motion is regulated by specific integrin
  receptor and by a -TNF
• Immune function - responsibility for
  recognition, uptake, processing, presentation of
  soluble antigen and haptens to T lymphocytes.
  Irradiation by UV B absorbed in epidermis
  decreases production of total number of
  Langerhans cells and cytokines (whereas UV A is
  absorbed in dermis).

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Composition VII

• Ad a) EPIDERMIS
• cells - Merkel cells neurocrine cells,
• origin intraepithelial cells of skin -
  epidermal keranocyte origin, first evident
  11-12th weeks gestation age,
• localization epidermis, dermis,
• Contains actin- cross linking protein villin
  
• mechanoreceptors and may contributed to
  development of nerve plexus in upper dermis
  joined to retinocytes by desmosomal junctions

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Composition VIII

• DERMIS
• Connective tissue component of skin pliability,
  plasticity, elasticity and tensile strength
• Collagens (75 of dry material of skin) all
  collagens have primary AA sequence Gly - X -
  Y
• collagen type I (80-90), collagen type III
  (8-12),
• minor types coll. V (papillary dermis, matrix
  around vessels, nerves), coll. VI
  associated with fibrils and interfibrillar
  spaces. Responsible for fine structure in early
  prenatal development of skin).
• Elastin amorphous and microfirillar material
  
• Proteoglycans with GAG (water binding material)
• Glykoproteins (fibronectin, laminin, fibrillin
  in elastin structure)

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Biochemistry of keratin x collagen

• Alfa- keratin and collagen have evolved for
  strength
• a keratin constitute almost the entire dry
  material of hair, nails and much of outer layer
  of skin (but also wool, horns, tortoise shell)
  
• Rich in the hydrophobic AA Phe, Ile, Val,
  Met, Ala
• a helix is right - handed
• Collagen is found in connective tissue
  extracellular matrix (ECM), organic material of
  bones, tendons, cartilage and cornea of the eye,
  
• Typical AA Gly (35), Ala (20), Pro
  (or Hyp) (21)
• repeating Gly - X - Pro or Gly -
  X Hyp
• a helix is left - handed.
  Lysinonorleucin cross-link
• Gelatin - food product - is derived from
  collagen

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Biochemistry of elastin x collagen

• Elastin
• Elastic properties polypeptide subunit of
  elastin is tropoelastin (m.w. ca 70 000), 800
  AA rich in Gly and Ala residues
• But
• a) tropoelastin has many Lys, few Pro (x
  tropocolla-gen Gly-X-Pro),
• b) Tropoelastin consists of lenghts of helix
  rich in Gly is separated by short regions
  containing Lys and Ala residues,
• c) Helical portions stretch on applying tension
  but revert to original when tension is
  release,
• d) Regions with Lys form covalent cross-
  links des-mosine or isodesmosine (four
  Lys), lysinonorleucine - also occurs in
  elastin

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Elastin, desmosin (2-4 polypepti-de) of
tropoelastin and lysinonor-leucine cross-linking
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Glycosoaminoglycans x and proteoglycans (see
next slide)

• Glycosoaminoglycans (GAG) heteropolysaccharides
  - family of linear polymers composed of repeated
  disac-charide units one of the two
  monosaccharide is always either N
  acetoacetylglucosamine of N- acetyl-galactos-amine
  the other is in most cases a uronic acid -
  glucu-ronic acid in some GAG one or more OH
  is esterifies by sulfate hyaluronic acid units
  of D- glucuronic acid and N-acetylglucosamine
  .
• GAG are attached to ECM proteins proteoglycans
• Proteoglycan - very long strand of hyaluronate
  to which numerous molecules, bound noncovalently,
  to core protein (glycoside bond between sugar
  and Ser) to many shorter GAG

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GAG and proteoglycans
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Interaction between cells and proteoglycan
of extracellular matrix
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Composition IX

• Ad dermis
• Monocytes, macrophages and dermal dendrocytes -
  heterogeneous collection of cells together
  with dendritic cells ( Langerhans cells) ?
  constitute mononuclear phagocyte system in skin
  
• they present antigen to immunocompetent lymphoid
  cells microbidicidal (though the production of
  lysozome, peroxide, superoxide), tumoricidal,
  secretary (growth factors, cytokines and other
  molecules) and hemato-poietic (coagulation, wound
  healing and tissue remodeling)
• Mast cells - in dermis - synthesize arrays of
  mediators the highest amount in papillary
  dermis.

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Composition X

• Ad c) HYPODERMIS formation from
  mesenchymally derived adipocytes cushions,
  protection and reserve energy supply of skin
• Boundary between the deep reticular dermis and
  hypodermis is an abrupt transition from fibrous
  dermal connective tissue to adipose rich region ?
  oxidation by FA here ? energy for skin
• Place where 7- dihydrocholesterol is background
  for D vitamin formation
• Actively growing hair follicles extend into
  subcutaneous fat
• Appocrine and ecrine sweat glands are confined to
  this depth of skin

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Effect of UV on skin I

• sun irradiation UV, visible and infrared
  rays
• UV C 100 -280 nm - sooner only in
  ionosphere, however, today, partly, could
  reached to people
• UV B 280 -315 nm - erythema light (
  vyvolává zarudnutí) 1 -10 effect via DNA ?
  inhibition of immunity, light lt 300nm in
  germicide lamp (bacterio-static due to
  photochemical reactions in bacteria cells
• UV A 315 - 400 nm - soft or black light
  90 -99 are also in special diagnostic bulb
  treatment of psoriasis (lupenka)
• visible 400 -760 nm
• Infrared gt 760 nm

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Effect of UV on skin II

• Acute photodynamic due to elevation of skin
  sensitivity, then phototoxic
  immmunosuppresion, photoalergy effect of
  different remedy, cosmetics, chemical substances
  etc (see lecture - Porphyrins) - erythema (
  zarudnutí), then brown color - formation of
  melanins
• Chronic effect papule ( puchýre), blister
  (pupence), and necrotic lesions, aging of
  skin, inactivation of enzymes, denaturation of
  proteins, and then ? benign cancer
  transferred into malignant cancer bazaliom
  (no metastasis), spinaliom, and melanom
• Effect sun beams on formation of D vitamin in
  skin (from cholesterolUV opens B ring of
  sterane - see Vitamins - sufficient is short
  term lighting on small area of body)
• Is solarium useful for our health? NO !!

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Schema of UV irradiation penetration into skin
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Effect of physiological aging versus aging
induced by UV I

• structure aging
  UV light
• Skin (width) ?
  ?
• Cells fibroblast inactive
  active
• inflamatory 0
  ?
• mastocytes ?
  ?
• Collagen amount ?
  ?
• solubility ?
  ?
• synthesis ?
  ?
• fibres
  stronger basophilic
  deg.
• Elastin amount ?
  ? ?
• microfibrilles ?
  ?? in early st.
• fibres
  desintergation/degen. abnormal

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Effect of physiological aging versus aging
induced by UV II

• structure aging
  UV light
• GAG ?
  ?
• Toumors senile verucce/hemangiomes
  pre-/malignity
• Skin vessels ?
  abnormal dilatat.
• Prevention ??
  Sun filtres,
• 
  vitamine A and
• 
  their derivates

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Four phototypes of skin protection (against UV
A, UV B irradiation

• Sun beams penetrate into skin a) according
  its color - white skin less than one with
  higher pigments b) dependent on both wave
  lengths and absorption in chromophores
• Answer of skin a) early (primary) erythema
  - due to infrared spectrum (partly by UV A) -
  vasodilatation, movement from sun reversible. it
  disappears, b) later (secondary) - -
  after 2-8 h , peak 12-24h after irradiation -
  inflammation pigmentation reaction is
  dependent on pre-vious conditions releasing of
  histamine (serotonin and prostaglandins as well),
  cytokines from keratocytes - formation of
  sunburn cells (damage keratocytes due to
  effect of UV B), c) early pigmentation darking
  of pigments oxidation of reduce melanin ?
  persisted even several days, redistibution of
  melanosomes from surrounding of nucleus into cell
  dendrites, changes of microfilaments and
  microtubuli in melanocytes, d) late pigmentation
  UV B (probably also UV A) beams induced new
  formation of melanins in epidermis, peak 72 h
  after irradiation mechanisms is still under
  consideration, furtermore - stronger skin fibres
  due to elevation of mitotic activity in basal
  lay-er of epidermis it persisted a several days

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Sweat secretion

• Formation of ecrine sweat is biphasic process -
  isotonic or slightly hypertonic fluid is
  elaborated in secretory tubule.
• Cholinergic regulation
• The reabsortion of NaCl ? final product is
  hypotonic
• Sodium ions flow into cell ?pumped across the
  cellular luminal membrane into secretory lumen
• Chloride ions follow passively along with water
  in response to osmotic change
• Stechiometry
• 111 for sodium, potassium and chloride ions
  (details - see next slide)

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Na, K and Cl- transport during cholinergic
sweat secretion. (C cotransport, exchanger, P
pump, CA carbonic anhydrase, solid line main
motion, break line passive motion,K movement
into lumen is Ca - dependent
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Relationship between concentration of Na and Cl-
in ecrine sweat - rates of sweating (C. F.
cystic fibrosis).
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Concentration of solute in sweat- comparison with
plasma
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Sweat glands ( potní)

• ecrine gland - cholinergic regulation here-
  production of bradykinin - vasodilatation
• distribution in dermis on whole body ?
  surrounding by two types of cells dark
  secretory granula with glycoproteins, clear
  contain glycogen not glands penis, clitoris,
  labia minora, external auditory canal, lips,
• Secret - sweat water- 99, NaCl, urea, NH3 and
  uric acid, slightly acid
• apocrine gland - adrenergic regulation
• distribution axilla, areolla, anal area Moll
  gland, glandulae ceruminose, glandulae
  sudoruferae nasales, glandulae axillares,
  glandulae circumanales)
• into hair follicles is produced odorless secret
  ? later - due to presence of bacteria specific
  odour
• Secret lipids, sugars, iron

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Comparison of apocrine and eccrine glands

• 
  apocrine
  ecrine
• Number 100 000
  2-5 million
• Size 2-5 mm diameter
  0,05 -0.1mm
• Relationship ducts of most gland
  no relationship
• to hair folicl. empty in upper (infun-
  ducts open
  dibular) portion of onto skin
  surface
• hair follicle
  
• Secretory cells single
  two clear, dark
• Innervations adrenergic
  cholinergic
• Secretion turbid, viscid
  clear, colorless
• may be
  colored low viscosity
• Amount very small
  capable large amount (1-4l/h)
  
• Chemistry lipids, carbohyd-
  primary water, no lipids
• rates, iron
  no iron
• Function atavistic in man
  thermoregulation
• as pheromones

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Sebaceous glands (mazové)

• Glands develop in 13 -15th week of gestation
• Secretion holocrine, the breakdown of sebaceous
  cell ? due to lysozomal enzymes, composition
  TG, wax ester, other lipids (see next slide),
  function in men ? Why ?? As barrier
  against water but for it epidermal lipids
  not sebum
• Hormonal control androgens (men testosterone
  and other androgens, in women ovarian and
  adrenal androgens) - therefore, enlargement
  during puberty, both estrogens (probably
  inhibition of production) and progesterone
  (controversial), glucocorticoids still under
  discussion, thyroid hormones thyreidectomy
  decreases, thyroxin increases production,
  retinoid suppression of sebum
• Age high production at birth, declines to very
  low in early childhood, at 6-8 years elevation,
  teens/early twenties maximum, then slow decline
• Cerumen ear wax
• Role in skin disease acne, xerosis

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Sebaceous follicle composition of sebum
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Chemical structures in sebum TG (57), wax ester
(25), squalene (15), cholesterol ( ester) (3)
and formation of sebaceous wax
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Metabolism of skin I

• Primary fuel for energy production in epidermis
  is glucose from circulation diffuses into
  keratinocytes without effect of insulin. Large
  proportion of glucose is catabolized up lactate
  (even in presence of oxygen). However, citric
  acid cycle does operate in epidermis
  explanation why this cycle is inefficient is due
  to wide fluctuation of temperature and blood flow
  in skin.
• 20 of glucose is metabolized by PPP cycle
  production of NADPH and pentose for both FA
  synthesis and nucleic acids.
• Secondary fuel - fatty acids derived from
  both epidermal stores and exogenous sources
  (when glucose flow is limited, then FA are
  metabolized).

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Metabolism of skin II

• Glycogen small amount under physiological
  conditions, however, elevation in all manner of
  injury of epidermis or during hair growth in
  follicle explanation energy when skin needs
  to be repaired or to use glucose immediately,
  most probably disequilibrilium in metabolic
  processes
• Furthermore, glucose is substrate also for
  synthesis of lipids polysaccharides and
  glycoproteins and nucleic acids
• GAG and proteoglycans highly charged and
  attract water forming gels (see also special
  slides GAG and proteoglycans here)

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Metabolism of skin III

• Lipid metabolism - components
• a) membranes,
• b) major constituents of permeability barrier,
• c) energy supply
• Synthesis from both glucose catabolism and AA
  and circulating FA - lipogenesis is ongoing in
  all layers of epidermis - sebum synthesis in
  sebaceous glands not from accumulation lipids
  from circulation even in sexual maturation
  (higher synthesis of sebum) - increase of
  endogenous production and decrease of exogenous
• Degradation - generally - lipases (yields in
  FA for neutral lipids TG, sterol esters) in
  outermost layers of epidermis, - specifically
  (e.g. formation of prostaglandins)

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Epidermal lipids
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Wound healing (hojení rány)

• Three phases of would healing
• Inflammation role of platelets, blood
  coaguation, and leucocytes (for this phase see
  also lecture Blood coaguation)
• Proliferation and tissue formation role of
  keratinocyte migration (several hours after
  injury stimulation by both different effect of
  various cytokines, growth factors and matrix
  proteins, actin cable play important role,
  laminin is, however, inhibitor) and integrins
  (their role see seminar Integrins),
  fibroplasia (formation of granulation tissue and
  reconstruction of dermal matrix hypoxia is
  important early stimulus) , angiogenesis
  (neovascularization)
• Tissue remodeling (it starts at same time as
  tissue formation and continues for months)
  fibroblasts role of fibronectin,
  proteoglycans and collagens (first degradation
  of old collagen and high formation of coll.
  III, then ?coll I, basal membrane collagen -
  types IV, VII, other collagen types VI, VIII),
  role of MMPs and TIMPs

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Regulation of MMP

• MMPs matrix - degradating metaloproteinases
  
• collagenes, gelatinases and
  stromelysins
• conversion of MMP zymogens into active forms -
  také place in three different compartments
  pericellular space, intracellularly and plasma
  cell membrane
• cysteine residue in sequence in propeptide
  domain is involved in interaction with zinc of
  adjoining catylytic domain
• This is initiated by plasmin at cell surface
  from plasmi-nogen), kallikrein (intrinsic factor
  in blood coaguation, activate factor XI) or
  catepsins (proteinasy lysozomální enzymy)
• inhibition TIMs binding to active
  proteinass high affinity (11), - then binding
  to proenzyme gelatinases.

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Extracellular matrix degradation three levels
controlsynthesis, activation and inhibition.
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Typy kue, opálení, doba ochrany na slunci (min)
a prodlouení doby pri pouití filtru UV -18
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Vliv veku a opalování na ruzné koní struktury