RELAXIN - STRUCTURES, FUNCTIONS, PROMISES, AND NONEVOLUTION

During the last two decades synthetic chemistry and molecular biology have transformed the little-known parturition-mediating factor relaxin into a chemically defined entity. Relaxin is a disulfide bond analog of insulin that shows no cross-reactivity to the insulin receptors, ca uses widening of the birth canal in most mammals, and has additional o r different functions in various species. The receptor interaction sit e in relaxin has been located quite precisely in the midregion of the B chain helix and is now known to involve two arginine residues that p roject from the alpha helix in an n, n + 4 configuration. The A chain of relaxin which appears to be uninvolved in receptor binding, is none theless essential. In fact, a major structural determinant in relaxin and insulin responsible for achieving either an insulin-like or a rela xin-like conformation is located in the penultimate position in the in trachain loop of the A chains.