36] δ-Aminolevulinic acid synthetase-sensitive methods in liver for hemoprotein biosynthesis

Abstract

This chapter discusses the δ-aminolevulinic acid synthetase-sensitive methods in liver for hemoprotein biosynthesis. The first enzyme in the hepatic heme biosynthetic pathway is δ- aminolevulinic acid (ALA) synthetase, which catalyzes the condensation of glycine and succinyl-CoA to form ALA. The low level of activity of ALA synthetase is elevated in the liver of patients with acute intermittent porphyria. ALA synthetase activity is initially measured by colorimetric assay, in which ALA is converted to a pyrrole by condensation with acetyl acetone; the pyrrole is then measured colorimetrically by the use of Ehrlich's reagent. Sensitive radiochemical assays have been developed for the estimation of ALA synthetase activity in normal hepatic homogenates and mitochondrial suspensions, which can be adapted to enzyme preparations from other tissues. It is anticipated that this radiochemical method for measuring ALA synthetase activity can be applied to other enzyme preparations, but caution must first be taken to properly adapt the assay to the enzyme preparation being investigated.