Abstract

Erythrocyte PFK activity 50--60% that of normal controls was found in a mother and her son, without muscular or hematological symptoms. The PFK activity of the mother's muscle was normal in fresh preparations and partially unstable to storage at 4 degrees C. Electrophoresis of muscle PFK revealed two bands, on normal and one abnormal with an anodic mobility greater than normal. Both patients were characterized as heterozygotes for an unstable muscle PFK. Unstable M'subunits disappeared in erythrocytes which are old cells devoid fo protein synthesis. Consequently an increased E/M subunit ratio leads to a distribution of the five isozymes different from that of normal erythrocytes. In these patients, we observed a loss of the M4 enzyme together with an increase in the E4 isozyme. The kinetic and immunologic data were compatible with these modifications. Isoelectric focusing of hemolysates from the two patients revealed an acidification of the main activity band, suggesting that an increase in E4 isozyme resulted in a change of the total electric charge.