Hansen J, Kielland-Brandt M C
Carlsberg Research Laboratory, Copenhagen Valby, Denmark.
J Biotechnol. 1996 Sep 13;50(1):75-87. doi: 10.1016/0168-1656(96)01551-9.
Brewer's yeasts sometimes produce inadequate or excessive amounts of sulfite, an antioxidant and flavour stabilizer, so means of controlling the sulfite production are desired. Understanding the physiology and regulation of the sulfur assimilation pathway of Saccharomyces yeasts is the key to change sulfite production. The MET2 gene of Saccharomyces yeasts encodes homoserine O-acetyl transferase, which catalyzes the conversion of homoserine to O-acetyl homoserine which in turn combines with hydrogen sulfide to form homocysteine, the immediate precursor of methionine. We expected that inactivation of MET2 would lead to accumulation of sulfide and derepression of the entire sulfur assimilation pathway and, therefore, possibly also to sulfite accumulation. Brewer's yeasts were constructed in which several of the four MET2 gene copies were inactivated. Sulfite production was increased in strains with one remaining MET2 gene and even more so when no active MET2 was present. In both cases, hydrogen sulfide production was also increased. To the extent that excess sulfide can be removed, this strategy may be applied to control sulfite accumulation by brewer's yeast in beer production.
酿酒酵母有时会产生不足或过量的亚硫酸盐，亚硫酸盐是一种抗氧化剂和风味稳定剂，因此需要控制亚硫酸盐产生的方法。了解酿酒酵母硫同化途径的生理学和调控机制是改变亚硫酸盐产生量的关键。酿酒酵母的MET2基因编码高丝氨酸O-乙酰转移酶，该酶催化高丝氨酸转化为O-乙酰高丝氨酸，后者再与硫化氢结合形成同型半胱氨酸，同型半胱氨酸是甲硫氨酸的直接前体。我们预期MET2的失活会导致硫化物积累以及整个硫同化途径的去阻遏，因此也可能导致亚硫酸盐积累。构建了酿酒酵母菌株，其中四个MET2基因拷贝中的几个被失活。在仅剩下一个MET2基因的菌株中，亚硫酸盐产量增加，当不存在活性MET2时，亚硫酸盐产量增加得更多。在这两种情况下，硫化氢产量也增加。只要过量的硫化物能够被去除，这种策略就可以应用于控制啤酒生产中酿酒酵母的亚硫酸盐积累。
