Characterization of charge isomers of yeast phosphoglycerate kinase. Evidence for intracellular differences

Three electrophoretic components of phosphoglycerate kinase have been isolated from baker's yeast. The isoionic point of the major component is 7.18 at 10 degrees C. Corresponding values for the minor ones are 6.91 and 7.48, respectively. There is a difference of one charge-unit between the isomers 1 and 2, and between the isomers 2 and 3. The release of component 3 from the yeast cells appears in contrast to the isomers 1 and 2 to be promoted by an organic solvent, thus suggesting this component to be bound to the cell-membrane. The amino-terminal amino acid residue appears to be N-acetylated serine in each of the three cases. The carboxyl-terminal ends seem to be identical also with -(Ala, Leu, Val, Lys)- Ala-Lys as the ultimate sequence. From the circular dichroism spectra the contents of alpha-helix and beta-structure were estimated to 15 and 40-50%, respectively. Factors have been determined for transformation and comparison of the specific activities as determined under the various conditions used at different laboratories.