Biosynthesis and intracellular transport of glyoxysomal malate dehydrogenase in germinating pumpkin cotyledons

Glyoxysomal malate dehydrogenase was synthesized as a larger molecular mass precursor in germinating pumpkin cotyledons. In pulse-chase experiments, the radioactive larger molecular mass precursor (38 kDa) disappeared and was converted to the mature form (33 kDa) of the enzyme. When the radiolabeled cotyledon was fractionated into cytosolic and organellar fractions, the larger molecular mass precursor was first recovered in the cytosolic fraction and then only after a 20 min chase the mature form was found in the organellar fraction. This indicates that the higher molecular mass precursor is synthesized in the cytosol and the processing of the transient precursor is coupled to the transport into glyoxysomes.