Abstract
Various assays for δ-aminolevulinic acid synthetase in chicken liver homogenates and particulate fractions were studied. The assay methods fall into two groups, those using exogenous succinyl-CoA generating systems and those depending on endogenous succinyl-CoA formation. In the former, the native samples showed low activity and a poor relationship between protein concentration and activity. Sonication of the samples was required to obtain higher activity and a linear relationship between protein concentration and activity. The primary factor limiting the full expression of the enzyme activity in these samples was thought to be the permeability barrier of mitochondrial membranes. In the sonicated samples the assay is limited to low protein concentrations. The addition of 100 m m sodium or potassium fluoride to the assay made possible the use of higher protein concentrations. Fluoride probably exerts its effect by preventing the rapid destruction of ATP by ATPase and providing enough ATP for the succinyl-CoA generating system. This fluoride effect was observed in the sonicated homogenates and particulate fractions of chick embryo, chick and adult chicken livers and cultured chick embryo liver cells. In those assays depending on the endogenous formation of succinyl-CoA the native homogenates and particulate fractions had relatively low δ-aminolevulinic acid synthetase activity and sonication or the addition of fluoride had no enhancing effect.
Published Version
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