Thermal stability and the biochemical genetics of erythrocyte catechol-O-methyl-transferase and plasma dopamine-beta-hydroxylase.

The levels of activity of human erythrocyte (RBC) catechol-O-methyl-transferase (COMT) and human plasma dopamine-beta-hydroxylase (DBH) are inherited in a monogenic fashion. The COMT in erythrocytes of subjects homozygous for the allele for low basal enzyme activity, COMTL, is more thermolabile than that in the erythrocytes of subjects with genetically high basal enzyme activity. This observation suggests that the locus COMT may represent the structural gene for COMT in man. Wide individual variations in the thermal stability of human plasma DBH also occur. There is a significant familial aggregation of the trait of thermolabile plasma DBH. Although subjects with thermolabile plasma DBH have average basal plasma DBH activity only about 55% of that of subjects with thermostable enzyme, the trait of thermolability does not cosegregate with DBHL, the allele for very low basal plasma DBH activity. Studies of thermal stability may help to increase our understanding of the biochemical basis of the genetic regulation of catecholamine enzymes in man.