Incorporation versus biosynthesis of leucine: implications for measuring rates of protein synthesis and biomass production by bacteria in marine systems

Abstract

Rates of leucine incorporation have been suggested recently to be useful for estimating rates of protein synthesis and biomass production by bacteria in natural water samples. The authors examined 2 potential problems with this approach: de novo synthesis of leucine and intracellular protein turnover. Rates of leucine and methionine biosynthesis were estimated from the incorporation of super(14)C-pyruvate and super(35)SO sub(4)@)u- super(2), respectively. Leucine inhibited super(14)C-pyruvate and super(3)H-glucose incorporation and methionine inhibited super(35)SO sub(4) incorporation. However, rates of biosynthesis of leucine and methionine were still much higher than the maximum rate of exogenous amino acid incorporation. This problem can be surmounted with empirically determined conversion factors which relate rates of leucine incorporation to rates of protein synthesis or biomass production.