A RADIOIMMUNOASSAY FOR THE TRIPEPTIDE GLY-TRP-MET, A MAJOR METABOLITEOF ENDOGENOUS CHOLECYSTOKININ IN BRAIN

We developed a specific and sensitive radioimmunoassay for the tripept ide Gly-Trp-Met (GWM) after its derivatization with phenzoquinone. Mea surable amounts of endogenous GWM-like immunoreactivity (GWM-ir), coel uting in HPLC with authentic GMW were detected in the medium of depola rized slices of rat cerebral cortex. The tripeptide GWM appears as the major inactive CCK-8 metabolite since a major fraction of CCK-8-ir re leased from the slices was apparently recovered in the medium as GWM. In addition, in the presence of the serine reagent diisopropylfluoroph osphate, a strong decrease of GWM formation was observed to accompany the corresponding increase of CCK-8-ir recovery in medium. The present study confirms that (a) serine peptidase(s) is(are) responsible for i nactivating endogenous CCK-8 in brain as previously proposed (Rose et al. Proc Natl Acad Sci USA 1988; 85: 8326).