Regulation of Unsaturated Fatty Acid Synthesis by Low Temperature.

1.嗜冷菌假单胞菌生物合成不饱和脂肪酸的机理对菌株E-3进行了研究。(1)该菌的脂肪酸合成酶能够合成不饱和脂肪酸。这一能力可被不饱和脂肪酸合成厌氧机制的抑制剂3-十月烯基-N-乙酰半胱胺所抑制。(2)该菌的细胞膜部分具有氧依赖的脂肪酸去饱和化活性。(3)不饱和脂肪酸营养缺陷型突变株具有极低的脂肪酸去饱和化活性。(4)以上结果表明，这两种机制在该菌中是共存的，但好氧机制是该菌生存所必需的。研究了不饱和脂肪酸的顺式异构化反应与嗜冷菌(Vibrio sp.)热适应的关系。菌株ABE-1.(1)在O^0~5^0生长的细胞中提取的磷脂中只含有棕榈油酸的顺式不饱和脂肪酸.(2)在20℃时，随着顺式脂肪酸含量的降低，棕榈油酸反式脂肪酸的含量增加了12%.(3)从脂肪酸熔点按饱和-gT；反式-gT；顺式-不饱和的顺序下降的结论是，异构化有助于该菌膜的同源亲和性.

1. Mechanism of biosynthesis of unsaturated fatty acid in a psychrotrophic bacterium, Pseudomonas sp. strain E-3, was investigated.(1) Fatty acid synthase from this bacterium was proven to have an ability to synthesize unsaturated fatty acid. This ability was inhibited by 3-decynoyl-N-acetylcysteamine, an inhibitor of anaerobic mechanism for unsaturated fatty acid synthesis.(2) Oxygen-dependent fatty acid desaturate activity was demonstrated in the membrane fraction of this bacterium.(3) It was shown that auxotrophic mutants for unsaturated fatty acid have extremely low activity of fatty acid desaturate.(4) From the above results, it was concluded that the two mechanisms are coexisted in this bacterium, but the aerobic mechanism is indispensable for survival of this bacterium.2. Isomerization of cis-to trans-from of unsaturated fatty acid was investigated in relation to thermal adaptation of a psychrophilic bacterium, Vibrio sp. strain ABE-1.(1) The cellular phospholipid extracted from the cells grown at O^0 to 5^0 was found to contain exclusively cis-from palmitoleate as a main unsaturated fatty acid.(2) Content of trans-from of palmitoleate was increased up to 12% with decreasing the content of cis-from when the cells were grown at 20^0 C.(3) From the fact that melting point of fatty acid decreases in the order of saturated- > trans - > cis-unsaturated form, it was concluded that the isomerization contributes for homeoviscousity of this bacterial membrane.