Effects of polypeptide and protein hormones on lipid monolayers. I. Effect of insulin and parathyroid hormone on monomolecular films of monooctadecyl phosphate and stearic acid.

Insulin in low concentrations inhibits the uptake of Ca(++) by the monooctadecyl (stearyl) phosphate monolayer (at air-water interface) and facilitates the release of Ca(++) adsorbed to the monolayer. These effects of insulin are more pronounced at higher insulin concentrations. Evidence is presented that a relatively intact insulin molecule competes with Ca(++) for the free phosphate group of the monolayer. Albumin has a slight inhibitory action on calcium uptake and parathyroid hormone has no observable action on calcium uptake or release.