Peterson D O, Bloch K
J Biol Chem. 1977 Aug 25;252(16):5735-9.
Long chain transacylase activity, acyl-CoA + enzyme in equilibrium acyl-enzyme + CoA, catalyzed by the multienzyme complex fatty acid synthetase from Mycobacterium smegmatis was measured by exchange of radioactive coenzyme A into even numbered fatty acyl-CoA substrates 14 to 24 carbon atoms long. This transacylase activity decreases sharply with increasing chain length. It is suggested that C24 transacylation may be rate-limiting in de novo fatty acid synthesis catalyzed by the myocobacterial system. Mycobacterial polysaccharides stimulate the rate of transacylation, and this enhancement becomes more marked as the chain length of the substrate increases. The magnitude of the effect is similar to polysaccharide stimulation of overall synthetase activity. It is therefore proposed that terminal transacylation is the specific and perhaps only partial reaction catalyzed by the M. smegmatis fatty acid synthetase which is facilitated by polysaccharide. The product distribution of the synthetase is distinctly bimodal, with peaks for acyl chains 16 and 24 carbon atoms long. A scheme based on nonoverlapping unimodal chain length specificities for the rates of two activities, elongation and terminal transacylation, is offered to explain this bimodal distribution.
通过将放射性辅酶A交换到14至24个碳原子长的偶数脂肪酸酰基辅酶A底物中，测定了耻垢分枝杆菌多酶复合物脂肪酸合成酶催化的长链转酰基酶活性，即酰基辅酶A + 酶 ⇌ 酰基 - 酶 + 辅酶A。这种转酰基酶活性随着链长增加而急剧下降。有迹象表明，在分枝杆菌系统催化的从头脂肪酸合成中，C24转酰化可能是限速步骤。分枝杆菌多糖刺激转酰化速率，并且随着底物链长增加，这种增强作用变得更加明显。其作用程度与多糖对整体合成酶活性的刺激作用相似。因此，有人提出末端转酰化是耻垢分枝杆菌脂肪酸合成酶催化的特定反应，或许也是唯一受多糖促进的部分反应。合成酶的产物分布明显呈双峰，分别对应16个和24个碳原子长的酰基链。基于两种活性（延伸和末端转酰化）速率的不重叠单峰链长特异性，提出了一个方案来解释这种双峰分布。
