Evidences for Adenine Nucleotide Binding in the Subunits ofNeurosporaMitochondrial Processing Peptidase

The mitochondrial processing peptidase (MPP) ofNeurospora crassaconsists of two subunits termed α- and β-MPP. Here we present spectroscopic and chromatographic studies indicative of adenine nucleotide binding in the two MPP subunits. ADP was identified as the cofactor of α-MPP and ATP as the cofactor of β-MPP. The nucleotides are not covalently bound and exert strong control on the conformational and functional properties of the subunits. The ADP cofactor of α-MPP seems to be of utmost importance for the proteolytic activity because no processing of the precursor protein was registered in the assay containing α-MPP depleted of ADP and native β-MPP. On the contrary, with native α-MPP and depleted of ATP β-MPP almost 100% processing activity could be measured. Very strong increase of the intensity and significant changes in the shape and maximum position of the protein fluorescence spectra were observed after removal of the adenine cofactors of α- and of β-MPP.