Multiple species of HPRT polypeptides in mouse L cells

Mouse L cells contain three polypeptide species which react with antibody specific for HPRT; loss or diminution of these polypeptides can occur in association with a heritable deficiency in HPRT enzymatic activity. Although HPRT activity is not detectable in deficient A9 cells, two of the three polypeptide species are detectable. Clonal revertant A9 cells which spontaneously regained HPRT activity also have re-acquired apparently normal amounts of all three polypeptide species; by contrast, HPRT-positive A9 cells which acquired the enzymatic activity via human metaphase chromosome transfer exhibited the human polypeptide species characteristic of that expressed in human cells. The heterogeneity exhibited by the mouse HPRT polypeptides suggests that the active mouse enzyme may be subject to a form of modification and/or regulation which is not shared by human HPRT.