The occurrence of chloroplastic and cytosolic isoenzymes of phosphoglycerate kinase in a range of plant species

The chloroplastic and cytosolic isoenzymes of phosphoglycerate kinase (PGK; EC 2.7.2.3) of leaves from 18 of a broad range of 21 vascular plant species were separated by either standard or modified anion-exchange chromatographic procedures. Immunoprecipitation of the isoenzymes with antisera raised against barley chloroplastic and cytosolic PGK isoenzymes showed that the chloroplastic isoenzymes resemble the chloroplastic isoenzymes of other species more closely than the cytosolic isoenzyme of the same species and vice versa for the cytosolic isoenzymes. Each of the two cyanobacterial species tested, yielded only a single PGK fraction on anion-exchange chromatography and gave no reaction with antisera raised against the barley isoenzymes. The cyanobacteria are presumed to contain only a single PGK which is not closely related to either of the barley PGK isoenzymes. In all of the investigated leaf extracts the catalytic activity of the cytosolic PGK was exceeded by that of the chloroplastic PGK with the ratio for many of the C3 plants falling within the range 5:95 to 15:85 (cytosolic: chloroplastic). The relative amounts of cytosolic PGK activity appeared to be greater in older leaves, in C4 and CAM plants and in ferns.