| Abstract: | The inhibition of the calmodulin-mediated stimulation of bovine brain cyclic nucleotide phosphodiesterase activity (3':5'-cyclic adenosine monophosphate 5'-nucleotidohydrolase, EC 3.1.4.17) by the 31-residue opiate peptide beta-endorphin has been investigated. Using conditions in which porcine brain calmodulin (6 nM) is limiting (i.e., to give a 3-fold, Ca2+-dependent stimulation of enzymic activity toward cyclic guanosine monophosphate), the domain of beta-endorphin responsible for the inhibition was mapped by using a series of deletion peptides. beta-Endorphin exhibited an ED50 of several micromolar under the conditions employed, and several amino-terminal deletion peptides were essentially as inhibitory as the parent peptide. Methionine enkephalin and various carboxy-terminal deletion peptides had no demonstrable effect at concentrations of 100-200 microM. Peptides 1-25 and 1-27 (C' fragment) inhibited the calmodulin-dependent activity of phosphodiesterase, but higher concentrations were required than of beta-endorphin. Studies using combined amino- and carboxy-terminal deletion peptides demonstrate that peptide 14-25 was the shortest peptide examined that was capable of inhibiting calmodulin stimulation of phosphodiesterase activity under the conditions used. There was no evidence to indicate that the amino-terminal region comprising residues 1-13 of beta-endorphin contributes to the measured inhibition of calmodulin-stimulated enzymic activity. The circular dichroic spectra of calmodulin, beta-endorphin, and mixtures of the two were obtained, and the ellipticity of the peptide-protein mixtures at 221 nm exceeded that expected by assuming simple additivity. This finding is consistent with a direct interaction of beta-endorphin with calmodulin which seems to lead to enhanced helicity of one or both components.(ABSTRACT TRUNCATED AT 250 WORDS) |
