Further Studies on the Nature of Immunoreactive Gastrin in Human Plasma

Electrophoretic and filtration analysis of immunoreactive plasma gastrin extends our previous finding of two immunoreactive components of plasma gastrin. One component has the characteristics of Gregory-Tracy heptadecapeptide gastrin; the other component has a less acidic charge than heptadecapeptide gastrin but emerges from a Sephadex gel column in a zone consistent with a molecular weight of about 7000, which is 3 1/2 times the molecular weight of heptadecapeptide gastrin. The larger, more basic component (BG) usually represents the major fraction of plasma gastrin; the heptadecapeptide-like component (H-LG) is virtually undetectable in some samples. However, only (H-LG) was found in the urine of a patient whose plasma contained nearly equal amounts of both components. There is no spontaneous interconversion of the two components in vitro, and on refractionation each component retains its integrity. However, trypsin converts BG into an immunoreactive component with characteristics similar to those of heptadecapeptide gastrin. The separated plasma components individually are indistinguishable from each other and from heptadecapeptide porcine gastrin I in their immunochemical reaction with guinea pig antiporcine gastrin I antibodies. The secretion of both components is stimulated by feeding.