p1. Medium-chain fatty acyl-CoA synthetase (EC 6.2.1.2) was isolated by the method of Mahler, Wakil & Bock (1953) and the enzyme activity determined by the disappearance of CoA in the presence either of butyrate and ATP or of butyryl-AMP, as well as by ATP formation from butyryl-AMP and PPsubi/sub. 2. Preincubation of the enzyme with CoA and ATP alone or together, followed by the removal of these substrates by gel filtration, caused a marked inhibition of ATP formation, contrary to results previously obtained with palmitoyl-CoA synthetase. 3. The effect of ATP on butyryl-AMP-dependent CoA disappearance was inconsistent. Low concentrations of ATP (0·1–0·5mm) always caused inhibition, whereas higher concentrations (5–10mm) activated in some enzyme preparations and inhibited in others. 4. This inconsistency was shown to be due to the presence of two enzyme fractions. Both fractions had similar activities when assayed by the butyryl-AMP- or butyrate-plus-ATP-dependent CoA disappearance. However, fraction I was activated by ATP as measured by butyryl-AMP-dependent CoA disappearance whereas fraction II was inhibited by it. Fraction I also catalysed ATP formation from butyryl-AMP and PPsubi/sub whereas fraction II was lacking in such activity. 5. The relationship of these observations with respect to other known mechanisms of fatty acid-activating systems is discussed./p
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机译:> 1。通过Mahler,Wakil&amp的方法分离中链脂肪酰基-CoA合成酶(EC 6.2.1.2);博克(1953)和酶活性通过CoA的消失确定的丁酸酯和ATP或丁酰基-AMP的存在,以及由丁酰基-AMP和PP I sub的ATP形成。 2.单独使用CoA和ATP或一起用COA和ATP预孵育,然后通过凝胶过滤除去这些底物,使得对ATP形成的显着抑制,与先前用棕榈酰-COA合成酶获得的结果相反。 3. ATP对丁约-AMP依赖性COA消失的影响不一致。低浓度的ATP(0·1-0·5mm)总是引起抑制,而在一些酶制剂中活化并在其他酶制剂中激活更高的浓度(5-10mm)。这种不一致被证明是由于存在两种酶级分。当由丁酰基-AMP-或丁酸盐加上-ATP依赖性COA消失时,两种级分具有类似的活性。然而,通过通过丁酰基-AMP依赖性COA消失测量而通过ATP激活馏分I,而少量II被其抑制。馏分I还从丁酰基-AMP和PP I sum>中催化ATP形成,而少量II缺乏这种活性。 5.讨论了这些观察结果关于其他已知的脂肪酸活化系统机制的关系。 p>
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