Morzycka E, Paszewski A
Acta Biochim Pol. 1982;29(1-2):81-93.
In Saccharomycopsis (Candida) lipolytica direct cysteine synthesis is mediated by two different, simultaneously acting cysteine synthases: a low molecular mass (74,000 daltons) monofunctional enzyme (Km for O-acetyl-l-serine 23.5 mm) and a high molecular mass (220,000 daltons) bifunctional cysteine-homocysteine synthase (Km for O-acetyl-l-serine 55.0 mm). The latter enzyme is also involved in direct homocysteine synthesis from O-acetyl-l-homoserine (Km 11.9 mm). Evidence is presented that a fraction of homocysteine can be synthesized from cysteine via cystathionine. Our previous results (Morzycka & Paszewski, FEBS Lett., 1979, 101, 97-100; Mol. Gen. Genet., 1979, 174, 33-38) together with the data presented here strongly suggest that both S., lipolytica synthases are under control of the same regulatory system, together with the other enzymes of sulphur metabolism: ATP-sulphurylase and aryl-sulphatase. gamma-Cystathionase, an enzyme involved in cysteine synthesis from homocysteine, is controlled exclusively by cysteine.
在解脂耶氏酵母（念珠菌属）中，直接的半胱氨酸合成由两种不同的、同时起作用的半胱氨酸合酶介导：一种低分子量（74,000道尔顿）的单功能酶（对O - 乙酰 - L - 丝氨酸的Km为23.5 mM）和一种高分子量（220,000道尔顿）的双功能半胱氨酸 - 高半胱氨酸合酶（对O - 乙酰 - L - 丝氨酸的Km为55.0 mM）。后一种酶也参与从O - 乙酰 - L - 高丝氨酸直接合成高半胱氨酸（Km为11.9 mM）。有证据表明，一部分高半胱氨酸可以通过胱硫醚从半胱氨酸合成。我们之前的结果（Morzycka和Paszewski，《欧洲生物化学学会联合会快报》，1979年，101卷，97 - 100页；《分子与普通遗传学》，1979年，174卷，33 - 38页）以及此处给出的数据强烈表明，解脂耶氏酵母的这两种合酶与硫代谢的其他酶：ATP - 硫酸化酶和芳基硫酸酯酶一起，受同一调节系统的控制。γ - 胱硫醚酶，一种参与从高半胱氨酸合成半胱氨酸的酶，仅受半胱氨酸的控制。
