REGULATION OF SUGAR TRANSPORT AND METABOLISM IN LACTIC ACID BACTERIA

点击翻译按钮获取中文摘要

A unique amino acid-dependent sugar transport system has been characterized in the Gram negative oral anaerobe, Fusobacterium nucleatum ATCC 10953. Energy necessary for the active transport of glucose and galactose is derived from anaerobic fermentation of specific amino acids (Glutamic, lysine, histidine). Kinetic analyses, and data from competition studies suggest that glucose and galactose are translocated via a common-affinity carrier. Intracellular sugars are phosphorylated by ATP- dependent kinases prior to conversion of high molecular-weight polymers. Glutamate, lysine and histidine prevent catabolism of the sugar polymers, but in the absence of amino acids the polymers are rapidly fermented to yield butyric, lactic and acetic acids. Two new amino acids have been identified and purified from Streptococcus lactis. These unusual amino acids, namely N(5)-(1- carboxyethyl)ornithine and N(6)-(1-carboxyethyl)lysine, have been chemically prepared and the stereochemical configurations of the natural products have been confirmed by chiral syntheses. The in vitro synthesis of N(5)-(1-carboxyethyl)-ornithine has been demonstrated by incubation of a cell-free extract with ornithine, pyruvic acid and NAD(P)H. A basic amino acid carrier has been identified and characterized in cells of Streptococcus lactis. The transporter mediates the energy-independent entry and exchange of lysine, arginine and ornithine.