Multilocus enzymes in man.

Two or more separate loci may be concerned in coding for enzyme proteins with the same or very similar catalytic properties. The phenomenon appears to be remarkably common and rough estimates suggest that perhaps 50% or more of structural loci coding for enzyme proteins are concerned with these so-called multilocus enzymes. The separate enzymes in such a multilocus set ressemble each other not only in their enzyme properties, but also in subunit structures and in molecular sizes. However there are often remarkable differences in expression of the several loci of a set from tissue to tissue. Such sets of loci probably arose in evolution by gene duplications with subsequent divergence by point mutations. Tissue differentiation in expression suggests that, pari passu with the divergence of the structural genes, there was an evolution of genetic regulating systems controlling their tissue expression.