Comparisons and modifications of the colorimetric assay for delta-aminolevulinic acid synthase

Detailed procedures are given for the colorimetric assay of gamma-aminolevulinic acid synthase. The gamma-aminolevulinic acid formed is converted to a pyrrole with acetylacetone and quantitated spectrophotometrically at 552 nm after reaction with Ehrlich's reagent. Three methods, chromatography on Dowex-1, ether extraction and dichloromethane extraction, are compared for the isolation of the pyrrole. Extraction with ether was the preferred method and, when applied to either homogenates or mitochondria from rat liver, yielded values of 105 U (nmol/b)/g liver and 0.41 U/mg mitochondrial protein. The method is rapid, simple and inexpensive; however, its use is restricted to activities of 0.56 U/ml of incubation mixture or greater.