D-Amino acid oxidase in the molluscan liver.

3. Insulin did not alter the inactivity of rat mammary gland slices towards acetate as sole substrate, but in presence of glucose it considerably increased the 14C found in the fatty acids. The incorporation of "IC into the fatty acids of sheep udder slices wasunaffected by insulin both in acetate alone and in acetate plus glucose. 4. Glycerol caused a slight incorporation of acetate carbon into the fatty acids of rat mammary gland slices in acetate alone, and in acetate plus glucose its stimulating effect on "C incorporation was as great as that of insulin. It stimulated the utilization of acetate for fatty acid synthesis by sheep udder slices in acetate alone but in acetate plus glucose its effect was slightly inhibitory. 5. Glyceride glycerol isolated as tri-p-nitrobenzoate from the neutral fat of the slices was not radioactive in any experiment. Mammary gland slices under our conditions do not incorporate acetate carbon into glycerol. 6. Deductions from respiratory and acid-change measurements as to the ability of mammary gland slices to utilize acetate for fatty acid synthesis in vitro and the effect of glucose, of insulin and of glycerol upon this process in ruminant and nonruminant mammary tissue respectively have been confirmed. There is now little doubt that mammary gland slices are capable of effecting fatty acid synthesis from small molecules in vitro.