Cytoplasmic NADP-linked dehydrogenase activities in avian tissues

Cytoplasmic activities of NADP-linked malic enzyme (E.C. 1.1.1.40), glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) and NADP-linked isocitrate dehydrogenase (E.C. 1.1.1.42) were determined in tissues of selected avian species, and compared with those in mammals. Malic enzyme was generally more active in avian liver and kidney than in the corresponding mammalian tissues. Hepatic activities as high as 200 units/g wet wt and 100 units/g wet wt were recorded in the Nectariniidae and the Ploceidae respectively. Glucose-6-phosphate dehydrogenase was generally less active in avian tissues than malic enzyme. In passerine birds activities were very low indeed, and in most cases spectrophotometrically undetectable. Malic enzyme and glucose-6-phosphate dehydrogenase were highly active in the adipose tissue of mammals but were inactive in the adipose tissue of birds. Marked increases in hepatic malic enzyme and glucose-6-phosphate dehydrogenase activities were associated in birds with premigratory fattening. Activities of isocitrate dehydrogenase were comparable in the corresponding avian and mammalian tissues, including adipose tissue.