Vitamin B12-induced alterations in activities of α-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 μg/g, injected intraperitoneally for three consecutive days) altered the activities of mitochondrial-α-glycerophosphate dehydrogenase (α-GPD) and NADP-dependent cytosolic malic enzyme (ME) in the brain of singi fish. The α-GPD activity increased at doses of 0.5, 1, 2 and 4 μg/g vitamin B₁₂. A dose of 0.5 μg/g vitamin B₁₂ induced less activity than higher doses. ME activity increased with 1, 2 and 4 μg/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 α-GPD and ME activity. Thus, vitamin B₁₂ is involved in the induction of some enzymes in fish brain.