MOLECULAR-BIOLOGY AND REGULATORY ASPECTS OF GLYCOGEN BIOSYNTHESIS IN BACTERIA

This chapter discusses the current information, views, and concepts of regulation of enzyme activity and expression of the glycogen biosynthetic enzymes. Considerable evidence that glycogen biosynthesis is subject to genetic regulation was obtained prior to the current era of molecular biology studies. However, much information has recently been obtained with respect to genetic regulation of the expression of the biosynthetic enzymes. The structural genes of the glycogen biosynthetic enzymes of E. coli and S. typhimurium have been cloned, which has not only increased our knowledge of the genetic regulation of glycogen synthesis, but also permits, via oligonucleotide-directed mutagenesis of the E. coli glgC gene, the structural gene encoding ADPGlc PPase, knowledge of various aspects of structure-function relationships concerning its catalytic and allosteric activity. However, the levels of glycogen biosynthetic enzymes in E. coli increase as cultures enter the stationary phase. The rate of glycogen synthesis is also inversely related to growth rate, when growth is limited for certain nutrients, e.g., nitrogen. When cells are grown in an enriched medium containing yeast extract and 1% glucose, the specific activities of ADPGlc PPase and glycogen synthase increase 11- to 12-fold, and that of glycogen branching enzyme increases fivefold, as cultures enter stationary phase. © 1994 Academic Press Inc.