Vitamin D affects Krebs cycle NAD-linked oxidoreductases from chick intestinal mucosa. 
Vitamin D3 administration affects the NAD-linked oxidoreductase activities of Krebs cycle from intestinal mucosa of vitamin D-deficient chicks.  Vmax values were increased in all of them, while K0.5 for substrate remained unchanged except for 2-oxoglutarate dehydrogenase, which showed lower affinity for oxoglutarate.  Addition of Ca2+ to the incubation medium increased the affinity of 2-oxoglutarate dehydrogenase and NAD-isocitrate dehydrogenase for their substrates either in the vitamin D3 treated group or in the control one.  The activity of succinate dehydrogenase, a FMN-dependent oxidoreductase, was not modified by vitamin D3 administration.  The oxygen consumption of the intestinal mitochondria was not altered by cholecalciferol treatment to vitamin D-deficient chicks.  The reason why vitamin D3 selectively affects the NAD-linked oxidoreductase activities of the Krebs cycle remains unknown.  The vitamin D hormone, 1,25(OH)2D3, appears to be the mediator of the response.