The effect of fumarate and of p-nitrophenol on the synthesis of fatty acids in homogenates of the mammary gland.

0-0005 to 0-004M resulted in progressive acceleration of respiration. Glucose plus hexokinase accelerated respiration, which was further increased by AMP. 3. The addition to the mitochondrial fraction of the particle-free supernatant of kidney cortex greatly enhanced the stimulating action of p. nitrophenol on the respiration. The supernatant fraction of mammary tissue did not show a corresponding activity. 4. In cell-free suspensions showing glycolysis under aerobic conditions, the addition of AMP or adenosine triphosphate in large amount resulted in the accumulation of lactic acid, thus inhibiting the Pasteur effect. 5. In mammary homogenates metabolizing fumarate plus pyruvate in the presence of fluoride and fluoroacetate, phosphorus/oxygen ratios approaching 3-0 were observed. Acceleration of respiration and citric acid formation resulted from the addition of 2 x 10-4M p-nitrophenol, which caused only partial inhibition of phosphorylation. No further acceleration of respiration and citric acid formation was observed when the concentration ofp-nitrophenol was raised to 4 x 10-4M, at which it abolished phosphorylation. Arsenate, when present in effective concentration, inhibited respiration, citric acid formation and phosphorylation.