EVIDENCES FOR ADENINE-NUCLEOTIDE BINDING IN THE SUBUNITS OF NEUROSPORA MITOCHONDRIAL PROCESSING PEPTIDASE

The mitochondrial processing peptidase (MPP) of Neurospora crassa cons ists of two subunits termed alpha- and beta-MPP. Here we present spect roscopic and chromatographic studies indicative of adenine nucleotide binding in the two MPP subunits. ADP was identified as the cofactor of alpha-MPP and ATP as the cofactor of beta-MPP. The nucleotides are no t covalently bound and exert strong control on the conformational and functional properties of the subunits. The ADP cofactor of alpha-MPP s eems to be of utmost importance for the proteolytic activity because n o processing of the precursor protein was registered in the assay cont aining alpha-MPP depleted of ADP and native beta-MPP. On the contrary, with native alpha-MPP and depleted of ATP beta-MPP almost 100% proces sing activity could be measured. Very strong increase of the intensity and significant changes in the shape and maximum position of the prot ein fluorescence spectra were observed after removal of the adenine co factors of alpha- and of beta-MPP. (C) 1996 Academic Press, Inc.