Effect of niacin deficiency on the thermal stability of NAD- and 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 oxidation-reduction of these cofactors. The thermal stability of malic enzyme, 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 concentrations of liver NAD, NADP, NADPH and the thermal inactivation of liver malic enzyme, glyceraldehyde-3-phosphate dehydrogenase, lactic dehydrogenase, and aldolase were not affected by niacin deficiency. In contrast, pectoral muscle glyceraldehyde-3-phosphate dehydrogenase in the niacin deficient quail compared to that of the controls had a markedly reduced thermal stability. This was associated with a corresponding decrease in the concentration of NAD and possibly NADPH. However, lactic dehydrogenase and aldolase activities were not affected. A similar pattern of heat inactivation was obtained when dialysed muscle and liver extracts were spiked with NAD or NADP. In these studies, NAD(P) protected muscle glyceraldehyde-3-phosphate dehydrogenase against heat inactivation to a much greater degree than that obtained with the other enzymes from muscle or liver tissue. These results suggest a causative relationship between the thermal stability of glyceraldehyde-3-phosphate dehydrogenase and coenzyme status in pectoral muscle tissue. This effect of niacin deficiency on the thermal stability of enzymes appears to be quite selective and specific.