Glyoxysomal malate synthetase is specifically degraded in microbodies during greening of pumpkin cotyledons

A cDNA clone (pKMS: insert, 1.9 kbp) for glyoxysomal malate synthase was prepared from a cDNA library constructed by poly(A)+ RNA from etiolated pumpkin cotyledons and was recombined into the in vitro transcription plasmid, Bluescript. Malate synthase synthesized in an in vitro transcription‐translation system was translocated into isolated glyoxysomes. The translocated malate synthase was protected from digestion by added proteinase K. Malate synthase, a glyoxysome‐specific enzyme, could also be translocated into leaf peroxisomes prepared from green pumpkin cotyledons, indicating that the machinery for protein translocation into leaf peroxisomes is similar to that into glyoxysomes. When microbodies prepared from greening pumpkin cotyledons were used in the translocation experiments, the translocated malate synthase was observed to be degraded. This result shows that the glyoxysome‐specific enzyme, malate synthase, is degraded in microbodies during the microbody transition from glyoxysomes to leaf peroxisomes.