[Studies on biosynthesis of short-chain fatty acids (author's transl)]

Studies were reported here on biosynthesis of short-chain fatty acids in lactating rabbit mammary glands. The maximal incorporation from [1-14C] acetate into total fatty acids were observed in microsomes and supernatant fractions of mammary glands but the synthetic rate either in the microsomes alone or in the supernatant alone was rather low. However approximately 80% of the maximal rate was restored in the supernatant for n-butyric acid synthesis. The incorporation from [1-14C] acetate into-n-butyric acid was markedly stimulated in the presence of NADH, compared to NADPH while total fatty acids synthesis was more dependent on NADPH. Long-chain fatty acids synthesis from [1-14C] acetate was decreased markedly by the addition of avidin although n-butyric acid formation was restored to 80%. Then by the addition of malonyl CoA or biotin the avidin system, middle- and long-chain fatty acids were recovered again. [1-14C] propionate was incorporated into even-numbered chain fatty acids as well as odd chain fatty acids. The synthesis of total fatty acids from [1-14C] propionate was more dependent on NADPH-generating system than either NADH or NADPH. [1-14C] bicarbonate was also incorporated slightly into fatty acids, such as decanoic or dodecanoic acids. In the reduction from either acetoacetyl CoA or crotonyl CoA, the tritium of NADP3H was stereospecifically incorporated into the beta-position of n-butyric acid. The reaction of acetoacetyl CoA reduction was much more dependent on NADH while crotonyl CoA was more reduced with NADPH. There was no difference between the dependencies on NADH and NADPH in the reduction of 2-hexenyl CoA.