Savin M A, Flavin M
J Bacteriol. 1972 Oct;112(1):299-303. doi: 10.1128/jb.112.1.299-303.1972.
Cystathionine synthesis from O-acetylhomoserine and cysteine has been demonstrated in yeast extracts for the first time. The activity is less than that of O-acetylhomoserine sulfhydrylase, but it is higher than that reported for homoserine O-transacetylase and therefore should not be growth limiting. Cystathionine synthase seems to share the regulatory properties of the sulfhydrylase, and both activities are missing from the methionine auxotroph Saccharomyces cerevisiae EY9, suggesting that both reactions are catalyzed by the same enzyme. However, cystathionine synthase activity was lost during purification of the sulfhydrylase, suggesting that the two reactions may be catalyzed by separate enzymes. Since previous studies have shown that yeast extracts can catalyze the cleavage of cystathionine to homocysteine, our results show the existence of two complete alternate pathways for homocysteine biosynthesis in yeast. Which of these is the major physiological pathway remains to be determined.
首次在酵母提取物中证实了由O-乙酰高丝氨酸和半胱氨酸合成胱硫醚。该活性低于O-乙酰高丝氨酸巯基酶的活性，但高于报道的高丝氨酸O-转乙酰酶的活性，因此不应成为生长限制因素。胱硫醚合酶似乎具有与巯基酶相同的调节特性，蛋氨酸营养缺陷型酿酒酵母EY9中这两种活性均缺失，这表明这两种反应由同一种酶催化。然而，在巯基酶的纯化过程中，胱硫醚合酶活性丧失，这表明这两种反应可能由不同的酶催化。由于先前的研究表明酵母提取物可以催化胱硫醚裂解为同型半胱氨酸，我们的结果表明酵母中存在两条完整的同型半胱氨酸生物合成替代途径。其中哪一条是主要的生理途径仍有待确定。
