Purification and properties of mouse pyruvate kinases K and M and of a modified K subunit

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Abstract
The K4 and M4 isozymes of mouse pyruvate kinase were purified to homogeneity and their physical, chemical and kinetic properties compared. The K isozyme is slightly larger but a high degree of homology exists as evidenced by a similar amino acid composition, immunotitration value and 2-dimensional arginine peptide pattern after tryptic digestion. The more active conformational form of the K isozyme has kinetic and chromatographic properties similar to those of the M isozyme. Only K subunit could be extracted with antibody from fresh spleen extracts but this subunit can be cleaved to form a product with the mobility of the M subunit. The cleavage is accomplished by an endogenous enzyme and appears to be the 1st step in K-enzyme degradation. This product is called Kpm.cntdot. KpmK hybrid could also be purified to homogeneity. This enzyme has the structure K2pmK2 and both types of subunit have activity. The Kpm form has a higher K0.5s value for phosphoenolpyruvate and a lower K0.5s value for ADP than does the K or the M type. The Kpm and M subunits otherwise have very similar properties and it is speculated that the Kpm subunit is an M-type precursor.