NUTRITIONAL AND REGULATORY ASPECTS OF SERINE METABOLISM IN ESCHERICHIA COLI

Abstract

Growth studies with a serine auxotroph have demonstrated a relationship between the serine supplied and the extent of growth, which closely agrees with the value calculated from the reported chemical composition of E. coli. Serine could be replaced by glycine and to a limited extent by L-threonine. Both exogenous serine and glycine regulate their own endogenous synthesis from glucose or fructose. The inhibition of endogenous synthesis of both amino-acids by serine was greater than 90% with both carbon sources. Greater amounts of exogenous glycine were utilized for cell synthesis when fructose was the carbon source. Growth conditions affected the levels of phosphoglycerate-dehydrogenase found in cell-free extracts. The highest levels were found in glucose-grown cells and the lowest in cells grown in a medium augmented with L-threonine, L-methionine, L-leucine and DL-isoleucine. The levels of serine-phosphate phosphatase were not altered by changes in growth conditions.