Immunochemical studies of the turnover of delta-aminolevulinate synthase in rat liver mitochondria and the effect of hemin on it.

The half-life of delta-aminolevulinate (ALA) synthase in the liver mitochondria of allylisopropylacetamide-treated rats was estimated to be about 35 min, taking advantage of the observation that hemin strongly inhibits the translocation of ALA synthase from the liver cytosol into the mitochondria. ALA synthase accumulating in the liver cytosol in allylisopropylacetamide-treated rats is rapidly translocated into mitochondria with a half-disappearance time of about 20 min, but does not appear to undergo degradation until it is translocated into mitochondria. A study with an ALA synthase-specific IgG revealed that the decrease in the ALA synthase activity in the liver mitochondria observed after the administration of cycloheximide or hemin effectively paralleled the decrease in the amount of immunologically reactive protein, providing further evidence that ALA synthase is rapidly degraded in the mitochondria.