Biochemical evidence that starch breakdown by Bacteroides thetaiotaomicron involves outer membrane starch-binding sites and periplasmic starch-degrading enzymes

拟杆菌 生物化学 周质间隙 麦芽糖 麦芽三糖 生物 淀粉 支链淀粉 细胞外 直链淀粉 拟杆菌 细菌 大肠杆菌 遗传学 基因
作者
Kevin L. Anderson,A A Salyers
出处
期刊:Journal of Bacteriology [American Society for Microbiology]
卷期号:171 (6): 3192-3198 被引量:160
标识
DOI:10.1128/jb.171.6.3192-3198.1989
摘要

Bacteroides thetaiotaomicron can utilize amylose, amylopectin, and pullulan as sole sources of carbon and energy. The enzymes that degrade these polysaccharides were found to be primarily cell associated rather than extracellular. Although some activity was detected in extracellular fluid, this appeared to be the result of cell lysis. The cell-associated amylase, amylopectinase, and pullulanase activities partitioned similarly to the periplasmic marker, acid phosphatase, when cells were exposed to a cold-shock treatment. Two other enzymes associated with starch breakdown, alpha-glucosidase and maltase, appeared to be located in the cytoplasm. Intact cells of B. thetaiotaomicron were found to bind 14C-starch. Binding was probably mediated by a protein because it was saturable and was decreased by treatment of cells with proteinase K. Results of competition experiments showed that the starch-binding proteins had a preference for maltodextrins larger than maltohexaose and a low affinity for maltose and maltotriose. Both the degradative enzymes and starch binding were induced by maltose. These findings indicate that starch utilization by B. thetaiotaomicron apparently does not involve secretion of extracellular enzymes. Rather, binding of the starch molecule to the cell surface appears to be a first step to passing the molecule through the outer membrane and into the periplasmic space.
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