Biosynthesis of milk-fat in the rabbit from acetate and glucose. The mode of conversion of carbohydrate into fat

Abstract

Biosynthesis of fat was studied in lactating rabbits with the aid of acetate, pyruvate and glucose labelled with C14. Both short- and long-chain fatty acids and cholesterol are synthesized from acetate and from carbohydrate in the mamma of lactating rabbits. It was estimated that in 6 hrs. at least 30-70% of the short-chain acids originate from acetate, or about 25% from carbohydrate; only 10-20% of these amts. of the long-chain acids were, however, synthesized in the mammary gland from either of these sources. Some 65-95% of the glycerol part of fat, derived from carbohydrate, was newly formed in the mammary gland in 6 hrs. It is concluded that the glycerol part of fat is more rapidly metabolized by the animal than the fatty-acid part. About 20% of the body''s acetate used for acetylation of p-aminobenzoic acid was derived from glucose in fully fed lactating rabbits. Octanoic acid from milk and mammary-gland fat and the acetyl group of p-acetamido-benzoic acid were degraded chemically after the admn. of [carboxy- Cl4]-and [methyl-C14]-acetate, [alpha-C14]-and [beta-C14]-pyruvate and of [l-C14]-glucose. The results of degradations showed that the conversion of glucose to fatty acids proceed s by the overall reactions equivalent to glucose pyruvate [forward arrow] acetate [forward arrow] fatty acid.