Purification of a specific activator of solubilized delta-aminolevulinic acid synthetase from rat liver mitochondria.

A protein capable of activating 6-aminolevulinic acid synthetase has been purified from rat liver mitochondria. By treatment of the mitochondrial inner membrane-matrix fraction with Lubrol a soluble and active preparation of 6-aminolevulinic acid synthetase has been obtained. Ammonium sulfate fractionation yielded a 33 to 40% saturated fraction containing catalytic 6-aminolewlinic acid synthetase activity and a 60 to 90% saturated fraction containing an activity capable of stimulating the catalytic 6-aminolevulinie acid synthetase activity 3-fold. The fraction which activates 6-aminolevulinie acid synthetase contains no catalytic 8-aminolevulinic acid synthetase activity and is nondialyzable and sensitive to pronase digestion. The activator activity has been purified 6,250-fold by means of carboxymethyl Sephadex chromatography, Sephacryl S-200 gel exclusion chromatography, and hydroxylapatite chromatography. The purified activator was judged to be homogeneous by its migration as a single band on sodium dodecyl sulfate containing polyacrylamide gels, nondenaturing polyacrylamide gels, and isoelectric focusing gels. The activator displayed a native molecular weight of 57,000 6,000 as determined by gel exclusion chromatography and a molecular weight of 54,000 +. 6,000 as determined by sodium dodecyl sulfate-gel electrophoresis. The isoelectric point was determined to be 1.5. It is possible that the formation of high molecular weight aggregates of &aminolevulinic acid synthetase catalytic monomers is the mode of action of the activator.