NADPH IS A SPECIFIC INHIBITOR OF PROTEIN IMPORT INTO GLYOXYSOMES

We have studied the import of proteins into glyoxysomes in vitro and s how that this process is specifically inhibited by NADPH. NADPH affect s both binding and translocation of proteins into glyoxysomes, and inh ibition is determined by the ratio of NADP(+) to NADPH. The site of ac tion of NADPH is most likely within the glyoxysome because (1) pretrea tment of glyoxysomes with NADPH, followed by re-isolation of the organ elles prior to the import assay, resulted in inhibition of import that could be restored by the addition of NADP(+); (2) low concentrations of NADPH inhibited binding of proteins to broken glyoxysome membranes. The sensitivity of protein import to inhibition by NADPH declines as glyoxysomes are converted to leaf-type peroxisomes. A model is propose d that speculates on a possible role for NADPH in regulating protein i mport into plant peroxisomes.