Cellobiose and cellodextrin metabolism by the ruminal bacterium Ruminococcus albus
Cellobiose and cellodextrin metabolism by the ruminal bacterium Ruminococcus albus
复制标题
DOI：
10.1007/s002849900242
复制
发表时间：
1997-10-01
影响因子：
2.6
通讯作者：
Strobel, HJ
中科院分区：
文献类型：
--
作者：
Lou, JR;Dawson, KA;Strobel, HJ
白色瘤胃球菌是瘤胃中一种重要的纤维分解菌。纤维二糖通过水解酶和磷酸化酶被该生物体代谢，但每种途径的相对贡献尚不清楚。纤维二糖消耗率的指数增长的细胞是小于粗提取物（75对243 nmol/min/mg蛋白质）。纤维二糖磷酸化裂解比水解活性大得多（179与19 nmol/min/mg蛋白质），表明磷酸化酶是纤维素降解的可溶性产物的初始代谢中的关键酶。纤维糊精磷酸化酶似乎对大至纤维六糖的底物具有活性。磷酸化酶活性的细胞质，但水解活性与膜和细胞质组分。游离葡萄糖被GTP依赖性葡萄糖激酶磷酸化，该酶对GTP或ITP（>324 nmol/min/mg蛋白）的活性比对ATP、UTP、CTP、GDP或PEP的活性高20倍。与葡萄糖相比，当甘露糖、2-脱氧葡萄糖或果糖用作底物时，活性降低至少57%。葡萄糖和GTP的K（m）分别为321和247 μ M。由于磷酸解裂解比简单水解节省更多的代谢能量，因此这种途径可能提供了更有效的R.在底物限制条件下，如在瘤胃中发现的条件下，
Ruminococcus albus is an important fibrolytic bacterium in the rumen. Cellobiose is metabolized by this organism via hydrolytic and well as phosphorylytic enzymes, but the relative contributions of each pathway were not clear. The cellobiose consumption rate by exponentially growing cells was less than that of crude extracts (75 versus 243 nmol/min/mg protein). Cellobiose phosphorolytic cleavage was much greater than hydrolytic activity (179 versus 19 nmol/min/mg protein) indicating that phosphorylases were key enzymes in the initial metabolism of the soluble products of cellulose degradation. Cellodextrin phosphorylase appeared to be active against substrates as large as cellohexaose. Phosphorylase activities were cytoplasmic, but hydrolytic activities were associated with both the membrane and cytoplasmic fractions. Free glucose was phosphorylated with a GTP-dependent glucokinase, and this enzyme showed 20-fold higher activity with GTP or ITP (>324 nmol/min/mg protein) than with ATP, UTP, CTP, GDP, or PEP. The activity was decreased at least 57% when mannose, 2-deoxyglucose, or fructose was used as substrate compared with glucose. The K(m)s for glucose and GTP were 321 and 247 mu M, respectively. Since phosphorolytic cleavage conserves more metabolic energy than simple hydrolysis, it is likely that such pathways provide for more efficient growth of R. albus in substrate-limiting conditions like those found in the rumen.