Molecular weight and subunit size of rabbit mammary-gland fatty acid synthetase

Abstract

1. The molecular weights of fatty acid synthetases isolated from lactating rabbit, rat, cow and goat mammary glands were estimated by sucrose gradient centrifugation and compared by chromatography on Sepharose 6B. 2. The values obtained for all four enzymes were in the same range (0.40 X 10(6)-0.55 X 10(6)) as that found for other mammalian and avian fatty acid synthetases. The molecular weight found for the rabbit mammary enzyme therefore differs from published values of approx. 0.9 X 10(6). 3. The molecular weights of the subunits of these four synthetases were 225000-242000. Again, the value for the rabbit mammary enzyme differs from published values.

Identification of fatty acid synthetase messenger RNA on free polyribosomes isolated from lactating rabbit mammary gland

“…approx. 260000, which is comparable with the value quoted by Grunnet & Knudsen (1978) and by Hardie & Cohen (1978) for the synthetase subunit. Total caseins, and total whey proteins (as a source of a-lactalbumin), were prepared by acid precipitation of skimmed rabbit milk.…”

“…The enzyme from lactating rabbit mammary gland consists of two polypeptides both of mol.wt. 250000, which cannot be resolved by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate (Grunnet & Knudsen, 1978;Hardie & Cohen, 1978). Whether these subunits are identical remains to be established, though evidence based on cleavage of fatty acid synthetase with elastase is consistent with the view that they are (Guy et al, 1978).…”

Fatty‐Acid Synthesis in Lactating‐Goat Mammary Gland 2. Medium‐Chain Fatty Acid Synthesis

“…We have previously shown that goat mammarygland fatty acid synthetase in contrast to the rabbit enzyme can hydrolyse medium-chain acyl-CoA model substrates [6]. This indicates that the goat mammarygland fatty acid synthetase has an inherent ability to terminate fatty acids at medium-chain length.…”

“…The above described induction of CIO fatty-acid synthesis by the microsomal fraction could be due to either the presence in goat mammary microsomal fraction of a medium-chain-terminating acyl-thioester hydrolase like the one found in rabbit mammary gland cytosol [2] or to activation of the medium-chain acyl-thioester hydrolase present in the goat mammarygland fatty acid synthetase complex [6]. To test these two different possibilities the following experiments were carried out.…”

“…The thioesterase specificity of cow mammarygland fatty acid synthetase towards acyl-CoA model substrates was measured as described [6]. To avoid the problems of critical micellar concentrations, the specificity was measured at low substrate concentrations i.e.…”