EFFECT OF NIACIN DEFICIENCY ON THE THERMAL-STABILITY OF NAD-DEPENDENTAND NADP-DEPENDENT DEHYDROGENASES IN LIVER AND PECTORAL MUSCLE OF JAPANESE-QUAIL

The objective of this study was to determine whether the concentration of pyridine nucleotides in muscle and liver tissue of quail affected the heat stability of aldolase and selected enzymes involved in the ox idation-reduction of these cofactors. The thermal stability of malic e nzyme, glyceraldehyde-3-phosphate dehydrogenase, lactic dehydrogenase, and aldolase in liver, and in pectoral muscle of quail was studied at incubation temperatures ranging from 27 to 60 degrees C. The concentr ations of liver NAD, NADP, NADPH and the thermal inactivation of liver malic enzyme, glyceraldehyde-3-phosphate dehydrogenase, lactic dehydr ogenase, and aldolase were not affected by niacin deficiency. In contr ast, pectoral muscle glyceraldehyde-3-phosphate dehydrogenase in the n iacin deficient quail compared to that of the controls had a markedly reduced thermal stability. This was associated with a corresponding de crease in the concentration of NAD and possibly NADPH. However, lactic dehydrogenase and aldolase activities were not affected. A similar pa ttern of heat inactivation was obtained when dialysed muscle and liver extracts were spiked with NAD or NADP. In these studies, NAD(P) prote cted muscle glyceraldehyde-3-phosphate dehydrogenase against heat inac tivation to a much greater degree than that obtained with the other en zymes from muscle or liver tissue. These results suggest a causative r elationship between the thermal stability of glyceraldehyde-3-phosphat e dehydrogenase and coenzyme status in pectoral muscle tissue. This ef fect of niacin deficiency on the thermal stability of enzymes appears to be quite selective and specific. Copyright (C) 1996 Elsevier Scienc e Ltd