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PEROXYSOMII
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Caracteristici generale, ultrastructură şi funcţii
1954, J. Rhodin microbodies
microscopul electronic
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1965 De Duve peroxisomi
fracţionare subcelulară
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morfologia diametru variaza
intre 0,15 - 1,7 m. au elemente
constante: mmbrana matricea
au elemente inconstante :
Nucleoidul (cristaloidul)
Placa marginala
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Peroxisomii - caractere morfologice membrana:
Delimiteaza peroxisomii Seamana cu membrana
plasmatica Grosimea este de 6 à 8 nm.
matricea:
Omogena formata din filamente granulare.
Moderat opaca in ME. Contine filamente ramificate
cu Φ de 4 - 4,5 nm .
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Cristaloidul - caractere morfologice
Prezent la numeroase specii animale si vegetale.
Ocupa centrul peroxismului Are un aspect dens politubular
Unitatea de baza este tubulul primar
Dispozitia tubulilor este variabila: Să fie strâns uniţi formand structuri
dense Dispusi in jurul unui spatiu formand
tubulul secundar
Absent la primate si la om.
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placa marginala – caractere morfologice Structura plata
Groasa liniara dispusa la periferia cristaloidului
Exista in peroxisomii din numeroase primate in ficat, rinichi
Densa in ME
Este omogena
Mult mai groasa decat membrana peroxisomilor
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Produc/descompun H2O2
RH2 + O2 R + H2O2
D-aminoacidoxidazele alanina → piruvat
A-hidroxiacidoxidazele -hidroxiacizii → -cetoacizi lactatul piruvat
uratoxidaza acidul uric → uree
acizii grasi → Acetil - CoA enzime
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Functiile peroxisomilor Sinteza de peroxid de hidrogen (apa oxigenata)
Oxidarea: alcoolului fenolului Acidului formic formaldehidei
Sinteza plasmalogenilor
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Oxidarea :
alcool; fenol; acid formic; formaldehida
catalaza
H202 + R`H2 R` + 2H2O
catalaza
2H202 2H2O + O2
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Sinteza plasmalogenililor
CH3
CH3R2 C O CH
CH2
CH2 O P O CH2 CH2 N CH3OH
OO
O
+
O C R1 R2 C O CH
CH2
CH2 O P O CH2 CH2 N CH3OH
O
CH3
+CH3
O O CH CH R1
plasmalogenifosfogliceride
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Biogeneza şi implicaţiile medicale
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Boli genetice peroxisomale Defecte de biogeneza peroxisomilor
sindromul cerebrohepatarenal Zellweger
Boli prin defecte monoenzimatice
Adrenoleucodistrofia
Boala refsum
Acatalazemia
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Alte procese patologice
Hepatite virale
Tratamente cu medicatie hipolipemianta de lunga durata Proliferarea peroxisomilor Aparitia cristaloidului
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Defecte de biogeneza peroxisomilor sindromul cerebrohepatarenal Zellweger
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sindromul cerebrohepatarenal Zellweger
Se observa la NN cu simtomatologia urmatoare : Hipotonie severa Acumulare de lipide in creier Hepatomegalie Ciroza hepatica Chiste renale Anomalii scheletale
Decesul survine pana la varsta de un an
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Boli prin defecte monoenzimatice
Adrenoleucodistrofia
Boala Refsum
Acatalazemia
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Adrenoleucodistrofia
Scaderea oxidarii acizilor grasi cu catena lunga de atomi de C determina Distrugerea
substantei albe din creier corticosuprarenalei
Cauze: Lipsa incorporarii enzimelor in peroxisomi
Boli prin defect de biogeneza
Lipsa unei enzime peroxisomale Boli prin defect monoenzimatic
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Boala Refsum
Produsa prin acumularea in citoplasma celulei nervoase de acid fitanic (lipid)
polineuropatie
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acatalazemia
Absenta catalazei in peroxisomi
Poate sa fie:
fatala pentru organism
asimtomatica
cand catalaza din peroxisomi este compensata de o catalaza din citosol