ORIENTATION AND NEAREST-NEIGHBOR ANALYSIS OF PSBI GENE-PRODUCT IN THEPHOTOSYSTEM-II REACTION CENTER COMPLEX USING BIFUNCTIONAL CROSS-LINKERS

Two distinct cross-linked products containing psbI gene product were g enerated in the photosystem II reaction center complex from spinach by treatment with bifunctional reagents directed to amino groups. The fi rst product, which was generated by a 3,3'-dithiobis(succinimidyl prop ionate) treatment, is deduced to be formed between the epsilon-amino g roup of Lys3 of the psbI gene product, and a side-chain amino group pr esent on the stromal extension of the D2 protein. The CNBr cleavage an alysis of the cross-linked product predicted that the amino group of t he D2 protein engaged in the cross-linking is either one of the three lysine residues on the N-terminal fragment (from N-terminus to Met19) or the LyS268 on the 6th fragment (from Val248 to Met275). The second product, which was also generated on the stromal side by a 1,6-hexamet hylene diisocyanate treatment preferentially in alkaline conditions, i s predicted to be formed between the epsilon-amino group of Lys3 of th e psbI gene product and the N-terminal alpha-amino group of the alpha- subunit of cytochrome b559.