Genetic control of gamma chain synthesis: A chemical and evolutionary study of the Gm(a) factor of immunoglobulins

Abstract

The amino acid sequences of the Gm“a” peptide, the Gm“non-a” peptide and the OWM peptide of immunoglobulins have been elucidated. The results indicate that both the a and non-a peptides in humans and higher apes were evolutionarily derived from the OWM peptide in the Old World Monkeys by single-step point mutations. One mutation which converted a glutamic acid residue on the OWM peptide into an aspartic acid residue gave rise to the a peptide; while another mutation which converted a leucine residue on the OWM peptide into a methionine residue gave rise to the non-a peptide. The single locus hypothesis versus the gene complex hypothesis concerning the biosynthesis of the genetically controlled Gm factors in humans were tested by examining the peptide maps of the IgG heavy chains of homozygous Gm (a+/a+) normal individuals. The results showed that both the a and the non-a peptides were present on such peptide maps. Therefore, these results support the hypothesis that multiple loci controlled the inheritance of the γ chains (or the constant regions of γ chains) of immunoglobulins.