DIGESTION OF INTRAPLASTIDIC HEXOSEPHOSPHATE ISOMERASE BY TRYPSIN IN PREPARATIONS OF ROOT PLASTIDS

The effect of tryptic digestion on hexosephosphate isomerase activity in pea root plastids and cytosol was investigated. Maintenance of orga nelle integrity conferred substantial protection from proteolysis when compared with broken organelles. Electrophoretic studies indicated th e presence of two major isoenzymes of hexosephosphate isomerase in pea roots, one cytosolic the other plastidial. Further studies indicated that the loss of hexosephosphate isomerase activity from organelles du ring tryptic digestion is due to proteolysis of the enzyme within or r eleased from the organelle and not loss of contaminating cytosolic act ivity which was not susceptible to trypsin proteolysis.