Martin S A, Russell J B
Department of Animal Science, Cornell University, Ithaca, New York.
Appl Environ Microbiol. 1987 Oct;53(10):2388-93. doi: 10.1128/aem.53.10.2388-2393.1987.
Toluene-treated cells of Streptococcus bovis JB1 phosphorylated cellobiose, glucose, maltose, and sucrose by the phosphoenolpyruvate-dependent phosphotransferase system. Glucose phosphorylation was constitutive, while all three disaccharide systems were inducible. Competition experiments indicated that separate phosphotransferase systems (enzymes II) existed for glucose, maltose, and sucrose. [14C]maltose transport was inhibited by excess (10 mM) glucose and to a lesser extent by sucrose (90 and 46%, respectively). [14C]glucose and [14C]sucrose transports were not inhibited by an excess of maltose. Since [14C]maltose phosphorylation in triethanolamine buffer was increased 160-fold as the concentration of Pi was increased from 0 to 100 mM, a maltose phosphorylase (Km for Pi, 9.5 mM) was present, and this activity was inducible. Maltose was also hydrolyzed by an inducible maltase. Glucose 1-phosphate arising from the maltose phosphorylase was metabolized by a constitutive phosphoglucomutase that was specific for alpha-glucose 1-phosphate (Km, 0.8 mM). Only sucrose-grown cells possessed sucrose hydrolase activity (Km, 3.1 mM), and this activity was much lower than the sucrose phosphotransferase system and sucrose-phosphate hydrolase activities.
经甲苯处理的牛链球菌JB1细胞通过磷酸烯醇丙酮酸依赖性磷酸转移酶系统使纤维二糖、葡萄糖、麦芽糖和蔗糖磷酸化。葡萄糖磷酸化是组成型的，而所有三种二糖系统都是可诱导的。竞争实验表明，葡萄糖、麦芽糖和蔗糖存在各自独立的磷酸转移酶系统（酶II）。过量（10 mM）的葡萄糖会抑制[14C]麦芽糖的转运，蔗糖对其抑制作用较小（分别为90%和46%）。过量的麦芽糖不会抑制[14C]葡萄糖和[14C]蔗糖的转运。由于在三乙醇胺缓冲液中，随着Pi浓度从0增加到100 mM，[14C]麦芽糖的磷酸化增加了160倍，所以存在一种麦芽糖磷酸化酶（对Pi的Km为9.5 mM），且该活性是可诱导的。麦芽糖也可被一种可诱导的麦芽糖酶水解。由麦芽糖磷酸化酶产生的葡萄糖-1-磷酸通过一种对α-葡萄糖-1-磷酸具有特异性的组成型磷酸葡萄糖变位酶（Km为0.8 mM）进行代谢。只有在蔗糖培养基中生长的细胞具有蔗糖水解酶活性（Km为3.1 mM），且该活性远低于蔗糖磷酸转移酶系统和蔗糖磷酸水解酶的活性。
