Adrenocorticotropin. 52 Synthesis and biological activity of adrenocorticotropic peptides with cystine bridges

Synthesis of biological activity of human beta-endorphin analogs with disulfide bridges

Three analogs of human beta-endorphin containing internal cystine bridges have been synthesized and their biological activities have been determined. It was found that the analogs with disulfide bridges between positions 17 and 26 or 11 and 26 retained full opiate activity as estimated by guinea ileum assay, whereas the analog with a cystine bridge between positions 7 and 26 showed reduced opiate activity. None of the analogs retained significant immunoactivity as revealed by radioimmunoassay.

Structure and chemistry of the peptide hormones of the intermediate lobe

The peptide hormones of the intermediate lobe are derived from a common precursor protein and are therefore biogenetically and structurally related. They represent a group of linear, flexible peptides which elicit a variety of physiological response. Structure-activity studies have shown that different segments of adjacent amino acid residues have a specific function (e.g. address, message, potentiation) in the interaction of each of these hormones with its receptor(s). This kind of organization of hormonal information is called sychnologic; it is the basic for the pleiotropic action of the opiomelanocortin peptides, i.e. the ability of related peptides to interact with different types of receptors in different target cells. Labelled peptide hormones with radioactive, fluorescent, or photolabile groups at defined sites are a prerequisite for studying hormone-receptor interaction. Multi-labelled derivatives of alpha-MSH are suitable for degradation and intracellular incorporation studies. Photoaffinity labelling of melanophore receptors with azidophenyl-containing analogues of alpha-MSH produces an irreversible stimulation of pigment cells. Covalent conjugates between peptide hormone receptors. These conjugates exhibit remarkable properties such as superpotency, strongly enhanced receptor affinity and prolonged action.

ACTH regulates blood pressure in man

In normal and hypertensive subjects, many stimuli which increase ACTH secretion also increase blood pressure and conversely, many drugs which decrease ACTH secretion also decrease blood pressure. We postulate that the hypothalamopituitary adrenal axis plays a role in blood pressure regulation in normal and hypertensive man.

Beta-endorphin. Synthesis and biological activity of analogs with disulfide bridges

Two analogs of human beta-endorphin (beta-EP) which contain cystine bridges, [Cys15-Cys26,Phe27,Gly31]-beta-EP (I) and [Cys16-Cys26,Phe27,Gly31]-beta-EP (II), were synthesized by the solid-phase method. Peptides I and II were shown to contain 2-2.5 times the opiate receptor binding activity of beta-endorphin. We also synthesized two analogs with reduced alkylated cysteine residues and these peptides, [Arg9,19,24,28,29 Cys(Cam)11,26,Phe27,Gly31] and [Arg9,19,24,28,29,Cys-(Cam)12,26,Phe27,Gly31], were shown to have approximately the same opiate receptor activity as beta-endorphin.

Conformational restrictions of biologically active peptides via amino acid side chain groups

Determining the relationships between conformation and biological activity in peptide hormones and neurotransmitters is an important goal of contemporary biology. A major difficulty in these studies is the conformational flexibility of most peptides and the high dependence of the conformations on environment. The question arises whether conformations determined in solution are relevant to those important to the peptide at the membrane receptor(s). One recent approach to overcome these difficulties has been the use of conformational constraints by covalent bonding of side chain groups of residues in the peptide. In this manner linear peptides are rendered cyclic, and cyclic peptides are further conformationally constrained either by ring contractions or by other conformational constraints. Biologically active peptides specifically designed by this approach have been found to possess several useful properties including: 1) greater conformational integrity; 2) increased agonist or antagonist potency; 3) prolonged biological activity; 4) increased enzymatic stability; and 5) increased specificity for a particular receptor. Careful applications of this approach have provided important new designs features for peptide structure-function studies, and new insights into peptide conformation-activity relationships for oxytocin, somatostatin, enkephalin, bradykinin, vasopressin, and other biologically active peptides.