The molecular nature of cholecystokinin in human plasma.

Using a radioimmunoassay specific for the bioactive, tyrosine-sulfated sequence of cholecystokinin (CCK) we have studied the molecular nature of CCK in plasma from normal human subjects. CCK was extracted from postprandial plasma by Sep-Pak cartridges prior to Sephadex G-50 gel chromatography. Four CCK components eluting like CCK-58, CCK-33, CCK-22, and CCK-8, were identified in all samples. Of these, CCK-33- and CCK-8-like peptides predominated. The heterogeneity of circulating CCK emphasizes the importance of plasma assays that measure all bioactive forms of CCK.