A CYSTEINE ENDOPEPTIDASE ISOLATED FROM CASTOR BEAN ENDOSPERM MICROBODIES PROCESSES THE GLYOXYSOMAL MALATE-DEHYDROGENASE PRECURSOR PROTEIN

A plant cysteine endopeptidase with a molecular mass of 35 kD was puri fied from microbodies of germinating castor bean (Ricinus communis) en dosperm by virtue of its capacity to specifically process the glyoxyso mal malate dehydrogenase precursor protein to the mature subunit in vi tro. Processing of the glyoxysomal malate dehydrogenase precursor occu rs sequentially in three steps, the first intermediate resulting from cleavage after arginine-13 within the presequence and the second from cleavage after arginine-33. The endopeptidase is unable to remove the presequences of prethiolases from rape (Brassica napus) glyoxysomes an d vat peroxisomes at the expected cleavage site. Protein sequence anal ysis of N-terminal and internal peptides revealed high identity to the mature papain-type cysteine endopeptidases from cotyledons of germina ting mung bean (Vigna mungo) and French bean (Phaseolus vulgaris) seed s. These endopeptidases are synthesized with an extended pre-/proseque nce at the N terminus and have been considered to be processed in the endoplasmic reticulum and targeted to protein-storing vacuoles.