Protein-S-isoprenylcysteine O-methyltransferase (EC 2.1.1.100) (Isoprenylcysteine carboxylmethyltransferase) (Prenylated protein carboxyl methyltransferase) (PPMT) (Prenylcysteine carboxyl methyltransferase) (pcCMT) [PCCMT]
Ultrastructure, age-incidence, and topographic distribution of so-called intracisternal microtubules (ICMT) were studied in neurons of autonomic and ganglia of dogs. Microtubules packed within dilated cisterns of rough ER are about 24 nm in diameter; the thickness of the walls is about 10 nm. These facts suggest that intracisternal microtubules are identical with cytoplasmic microtubules. The ICMT show 12, 13, and 14 protofilaments. ICMT wer more frequently observed in autonomic than in somatic ganglia. In 23 dogs over 7 years old, ICMT was positive in 20 dogs. These structures therefore, seem related to ageing. The mechanism of production has not yet been established, but the cause may be a disturbance of protein synthesis and/or of the protein tubulin transport system.
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