Irmler Stefan, Raboud Sylvie, Beisert Beata, Rauhut Doris, Berthoud Hélène
Agroscope Liebefeld-Posieux Research Station ALP, Schwarzenburgstrasse 161, Bern, Switzerland.
Appl Environ Microbiol. 2008 Jan;74(1):99-106. doi: 10.1128/AEM.00745-07. Epub 2007 Nov 9.
Volatile sulfur compounds are key flavor compounds in several cheese types. To better understand the metabolism of sulfur-containing amino acids, which certainly plays a key role in the release of volatile sulfur compounds, we searched the genome database of Lactobacillus casei ATCC 334 for genes encoding putative homologs of enzymes known to degrade cysteine, cystathionine, and methionine. The search revealed that L. casei possesses two genes that putatively encode a cystathionine beta-lyase (CBL; EC 4.4.1.8). The enzyme has been implicated in the degradation of not only cystathionine but also cysteine and methionine. Recombinant CBL proteins catalyzed the degradation of L-cystathionine, O-succinyl-L-homoserine, L-cysteine, L-serine, and L-methionine to form alpha-keto acid, hydrogen sulfide, or methanethiol. The two enzymes showed notable differences in substrate specificity and pH optimum.
挥发性硫化合物是几种奶酪类型中的关键风味化合物。为了更好地理解含硫氨基酸的代谢，其在挥发性硫化合物的释放中肯定起着关键作用，我们在干酪乳杆菌ATCC 334的基因组数据库中搜索了编码已知可降解半胱氨酸、胱硫醚和蛋氨酸的酶的推定同源物的基因。搜索结果显示，干酪乳杆菌拥有两个推定编码胱硫醚β-裂合酶（CBL；EC 4.4.1.8）的基因。该酶不仅与胱硫醚的降解有关，还与半胱氨酸和蛋氨酸的降解有关。重组CBL蛋白催化L-胱硫醚、O-琥珀酰-L-高丝氨酸、L-半胱氨酸、L-丝氨酸和L-蛋氨酸的降解，形成α-酮酸、硫化氢或甲硫醇。这两种酶在底物特异性和最适pH值方面表现出显著差异。
