Effects of NAD or NADP on the stability of liver and pectoral muscle enzymes in 3-acetylpyridine treated quail by heat and trypsin.

(1) The effects of long term treatment with 3-acetylpyridine on the stability of enzymes towards heat and trypsin treatment were studied. (2) In the liver NAD or NADP provided a similar degree of protection against heat inactivation at 55 degrees C for 6-phosphogluconate dehydrogenase (24%), glyceraldehyde-3-phosphate dehydrogenase (24%) and malic enzyme (20%), low level of protection of lactate dehydrogenase (13%) but didn't affect acetylcholinesterase at all. In the muscle, however, there was substantial protection against heat inactivation by coenzyme of glyceraldehyde-3-phosphate dehydrogenase (52%), an intermediate level of protection of lactate dehydrogenase (25%), low level of protection of 6-phosphogluconate dehydrogenase (17%) and malic enzyme (17%) and almost no protection of acetylcholinesterase. (3) In the susceptibility towards trypsin a low but similar degree of protection for dehydrogenases by coenzymes was observed in the liver whereas in the muscle there was substantial protection against trypsin inactivation by NAD of glyceraldehyde-3-phosphate dehydrogenase, an intermediate level of protection of 6-phosphogluconate dehydrogenase and malic enzyme and very little protection of lactate dehydrogenase but no protection of acetylcholinesterase. Among enzymes tested, glyceraldehyde-3-phosphate dehydrogenase showed the greatest protection against heat and trypsin inactivation by NAD. (4) The results suggest that the effect of 3-acetylpyridine treatment on the stability of muscle glyceraldehyde-3-phosphate dehydrogenase appears to be quite specific and selective.