Anaerobic and aerobic glycolysis in lactating mammary gland and in nervous tissue

Abstract

The rates of phosphorylation of glucose and of pyruvate formation, and enzymic inactivation of cozymase limit the rate of anaerobic lactic acid formation in mammary tissue. In the presence of glucose, pyruvate and nicotinamide, high rates of anaerobic glycolysis (Q lactic acid of approx. 10 [mu]l./mg. dry wt./ hr.) were maintained in rat mammary gland slices for 3 hrs.; when pyruvate or nicotinamide were omitted the rates were low (Q lactic acid of 2-3). Mammary gland slices of the rabbit in the presence of glucose, pyruvate, nicotinamide and cozymase produced lactic acid at rates [image] Q lactic acid of approx. 3. In homogenates of rat mammary tissue, the enzymic decomposition of cozymase was strongly inhibited by nicotinamide (0.01-0.04M). In mammary tissue of the rabbit, it was not. In rabbit mammary tissue slices, the breakdown of cozymase appeared to be catalyzed by diphosphopyridine pyrophosphatase. Fructose-1, 6-diphosphate in the presence of pyruvate and cozymase induced higher rates of anaerobic lactic acid formation than glucsoe. Addition of glucose and of yeast hexokinase further increased the rate of glycolysis. In glycolyzing homogenates the formation of lactic acid was accelerated by more than 100% on addition of hexokinase. Possible hormonal inhibition of the hexokinase reaction in lactating tissue is considered. Under aerobic conditions 2,4-dinitrophenol (DNP) increased glucose breakdown and lactic acid formation in brain cortex slices and in retina in a parallel manner. In brain slices in the presence of glucose, glutamate and cozymase, DNP increased the aerobic rate of glucose breakdown to its anaerobic level, thus completely inhibiting the Pasteur effect. In mammary gland slices, however, lactic acid formation could be increased without a corresponding acceleration and even with some inhibition of glucose breakdown. In "depleted" mammary tissue, DNP caused increased accumulation of lactic acid when glucose, pyruvate and cozymase were present. In the absence of added pyruvate or cozymase, the increase was much smaller or absent. The effect of DNP on the Pasteur reaction is discussed.