In vitro translocation of L-alanine: 4,5-dioxovalerate transaminase into rat kidney mitochondria

Abstract

A specific rabbit antibody was prepared against rat kidney mitochondrial L-alanine: 4,5-dioxovalerate transaminase, which is one of the two enzymes catalyzing the synthesis of (δ-aminolevulinic acid in the heme biosynthetic pathway. Total polyadenylated RNA isolated from rat kidney was translated in vitro using rabbit reticulocyte cell-free translation system, and L-alanine:4,5-dioxovalerate transaminase was estimated by indirect immunoprecipitation to represent 0.85% of the total translation product. When the total in vitro translated product was incubated with homologous kidney mitochondria, 59% of the [35S]methionine labeled enzyme was translocated into the mitochondria where it was no longer accessible to externally added protease. In relation to total protein translocation, the translocation of L-alanine:4,5-dioxovalerate transaminase remained unaltered by addition of hemin up to 50 μM. These results show that, unlike the other enzyme of the heme biosynthetic pathway (5-aminolevulinic acid synthetase), this enzyme is not under tight control by heme, but nonetheless, functions as an important source to maintain a housekeeping level of d-aminolevulinic acid.