‘Secondary’ isozymes derived from the three PGM loci

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Abstract
SUMMARY: 1. The isozymes derived from the human phosphoglucomutases ‐ PGM1, PGM2, PGM3 have been examined in three tissues (lymphocytoid cells, placentae and red blood cells) in which the average age of the constituent proteins may be expected to differ. The appearance of one or more more negatively charged isozymes would appear to be correlated with increasing overall protein age. It is suggested that these are ‘secondry’ isozymes formed in vivo from the least negatively chared form which presumed to be the primary post translational product of the particular gene.2. Changes in the PGM3, isozyme pattern have been observed on storage of the placental extracts. Both the primary and the secondary in vivo isozymes were similarly affected. The storage effects observed are possibly due to reaction with red cell oxidized glutathione contaminating the extract. They may lead to confusion in typing unless controlled. Similar changes were not observed with the PGM1, and PGM2, isozymes.3. The effects of a number of thiol reagents on the three PGMs have been examined and various changes in isozyme pattern have been produced artificially. Both the primary and the secondary in vivo isozymes derived from each allele were similarly affected by any particular treatment. PGM3, isozymes were more reactive with thiol reagents than PGM1, or PGM2, isozymes. These findings suggest that the primary and secondary isozymes derived from each of the three PGM loci each contain at least one reactive sulphydryl group. However, the in vivo changes by which secondary isozymes are generated do not appear to be due to such thiol effects.