The subunit structure of human muscle and human erythrocyte pyruvate kinase isozymes

Abstract

In human tissues the pyruvate kinase reaction (ATP: pyruvate phosphotransferase; E C 2.7.1.40) is catalysed by at least three isozymes [l-3] which can be distinguised by their kinetic, electrophoretic and immunological properties: M1 present in muscle, L the major form in liver and Mz found in liver, kidney and adipose tissue. The isozyme present in red cells (R) is kinetically similar to the L isozyme but can be distinguished from it by electrophoresis [2-41. The R isozyme can be converted into a form which is electrophoretically identical to the L isozyme either by treating with a liver homogenate or repeated freezing and thawing [4 ] . The molecular structures and interrelationships of the isozymes are unknown. We have examined the human M1 and R isozymes by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and two dimensional fingerprinting of their cyanogen bromide peptides. The evidence is consistent with identical subunits in the M1 tetramer and two pairs of non-identical subunits in the R tetramer. One of the R subunits may be homologous with the M1 subunit but is probably not identical to it.