THE INTERACTION OF CALMODULIN WITH REGULATORY PEPTIDES OF PHOSPHORYLASE-KINASE

The regulatory peptides Phk13 (301-327) and Phk5 (342-367) have been s ynthesized and their interaction with calmodulin studied. In the case of Phk13 modified forms were also synthesized in which a tryptophan gr oup was placed at position 4 or 21, as well as a form with tryptophan at position 4 and nitrotyrosine at position 21. From tryptic digestion , circular dichroism, and radiationless energy transfer measurements, it appears that Phk13 forms an elongated complex with calmodulin in wh ich the peptide is in a non-helical conformation, probably bent into a hairpin-shaped structure, the connecting strand of calmodulin is exte nded and exposed to the action of proteolytic enzymes, and the peptide makes contact with both the N- and C-terminal half-molecules of calmo dulin. In contrast, the Phk5 peptide has an alpha-helical conformation in the complex, which is relatively compact in shape.