Vitamin B12-induced alterations in activities of alpha-glycerophosphate dehydrogenase and malic enzyme in brain of singi fish, Heteropneustes fossilis (Bloch).

Different doses of vitamin B12 (0.25, 0.5, 1, 2 and 4 micrograms/g, injected intraperitoneally for three consecutive days) altered the activities of mitochondrial-alpha-glycerophosphate dehydrogenase (alpha-GPD) and NADP-dependent cytosolic malic enzyme (ME) in the brain of singi fish. The alpha-GPD activity increased at doses of 0.5, 1, 2 and 4 micrograms/g vitamin B12. A dose of 0.5 microgram/g vitamin B12 induced less activity than higher doses. ME activity increased with 1, 2 and 4 micrograms/g of vitamin B12/g. The mitochondrial and cytosolic protein content remained unchanged after vitamin B12 administration. Cycloheximide treatment inhibited the vitamin B12-induced increase in alpha-GPD and ME activity. Thus, vitamin B12 is involved in the induction of some enzymes in fish brain.