Molecular weight estimation of protoheme ferro-lyase by radiation inactivation

The molecular weight of protoheme ferro-lyase [EC 4.99.1.1], a mitochondrial enzyme, was estimated by the radiation inactivation method. Irradiation in vacuo caused less inactivation than that in air. The approximate molecular weight determined by this method was in the range from 250,000 to 320,000. The significance of the location of the enzyme in connection with its role in heme synthesis is discussed on the basis of Singer's membrane theory.