A mitochondrial encephalomyopathy with a partial cytochrome c oxidase deficiency of muscle

Mitochondrial respiratory chain defects are not accompanied by an increase in the activities of lactate dehydrogenase or manganese superoxide dismutase in paediatric skeletal muscle biopsies

Both the activity of lactate dehydrogenase (LDH) and the quantity of manganese superoxide dismutase (MnSOD) protein have been reported to be increased in fibroblasts from individual with mitochondrial electron transport chain defects. To ascertain whether this is a general phenomenon, we have determined the specific activities of these enzymes in skeletal muscle biopsies from control individuals and patients with defined electron transport chain defects. On investigation, both LDH and MnSOD activities were not found to be elevated. These findings suggest a possible fundamental difference between skeletal muscle preparations and fibroblasts with regard to their metabolic response to an electron transport chain defect.

Beta-turns as structural motifs for the proteolytic processing of seed proteins

Fifteen NH2- and COOH-terminal ends from both small and large chains of the most abundant 2 S albumins from Brassica napus seeds have been sequenced. This allows the determination of the exact proteolytic maturation sites of these proteins. Each one of these proteins arises from a polypeptide precursor which is cleaved during the post-translational processing at four sites, giving two different chains linked by disulphide bridges on the mature 2 S albumin. The hydrolyzed bonds involved in the processing are located in proline and glycine-rich regions, forming tetra-peptides with a very high beta-turn probability. Similar results have been found through the analysis of the 2 S albumin precursors from other seeds. These facts are interpreted in terms of the existence of a beta-turn specific endoprotease activity involved in the maturation process of 2 S albumins.

Demonstration of two isoforms of subunit VIIa of cytochrome c oxidase from human skeletal muscle. Implications for mitochondrial myopathies

Two different isoforms of subunit VIIa have been found in cytochrome c oxidase isolated from human skeletal muscle. The first 22 residues of the N-terminal amino acid sequences showed 5 differences. Our results provide the first conclusive evidence for the existence of cytochrome c oxidase isoenzymes in man. Since the two cytochrome c oxidase isoforms were both present in skeletal muscle tissue, though not necessarily in the same cell type, this suggests that human cytochrome c oxidase isoforms are not strictly tissue-specific. These findings may have important implications for the elucidation of genetic diseases in man in which a deficiency of cytochrome c oxidase is restricted to certain tissues.