104a] Enzymes of γ-aminobutyrate metabolism (bacterial): [formula omitted

Abstract

Publisher Summary A species of Pseudomonas fluorescens when grown on either pyrrolidine or putrescine adapts to the utilization of these compounds by a route involving T-aminobutyraldehyde, T-aminobutyric acid, succinic semialdehyde, and succinic acid as successive, common intermediates. Each of three enzymes involved in these conversions discussed in the chapter. Another reaction involved with this series of metabolites is the formation of γ -hydroxybutyric acid from succinic semialdehyde catalyzed by γ -hydroxybutyrate dehydrogenase. Because of the usefulness of two of these enzymes in a sensitive and specific method for the determination of γ -aminobutyric acid and of α -ketoglutarate, the assay for these compounds is described in the chapter. γ -Aminobutyraldehyde dehydrogenase activity is routinely determined spectrophotometrically by following the increase in absorption at 340 m μ due to the formation of DPNH. γ -Aminobutyric-glutamic transaminase activity is determined by coupling the transaminase with an excess of succinie semialdehyde dehydrogenase so that the formation of reduced pyridine nucleotide is a function of transaminase activity. Succinic semialdehyde may be determined by using the standard assay system for succinic semialdehyde dehydrogenase modified in that the aldehyde is the limiting factor. This enzyme activity is determined spectrophotometrically by following the increase in absorption due to the formation of reduced pyridine nueleotide. By coupling succinic semialdehyde dehydrogenase with γ -aminobutyrate- glutamate transaminase, a sensitive assay for α -ketoglutarate and γ- aminobutyrate is available, and described in the chapter.