Preparation and characterization of a biologically active gastrin derivative modified with an 125I-labeled imidoester

Cell-surface modification with an iodinatible imidoester to enhance radiolabeling

A procedure to enhance incorporation of radioactive iodine into cell-surface proteins is described. The effects of chemical modification of cells with the iodinatible haptens N-succinimidyl-3-(4-hydroxyphenyl) propionate (Bolton-Hunter reagent) and methyl-p-hydroxybenzimidate HC1 (Wood reagent) are compared. The Wood reagent, that does not alter the charge of the modified amino group, is superior in retention of cell viability and function. Cell-surface modification with the Wood reagent prior to radiolabeling is particularly useful for detecting antigens not readily iodinated using standard techniques.

Preparation of an N-acetyl-octapeptide of cholecystokinin. The role of N-acetylation in protecting the octapeptide from degradation by smooth muscle tissues

The C-terminal octapeptide of cholecystokinin (CCK-8) was acetylated on its lone N-terminal amino group using acetic anhydride in N,N-dimethylformamide. The acetylated derivative (Ac-CCK-8) and unreacted CCK-8 were separated from acetic anhydride and other reaction products by fractionation on Sephadex LH-20. Final purification was by thin-layer isoelectric focusing in a pH 2.5--4.0 gradient. The immunochemical properties of the octapeptide were unaffected by acetylation as measured by radioimmunoassay. The N-acetylated-octapeptide was equally as effective as unmodified CCK-8 in producing concentration-dependent isometric tension development in isolated cat gallbladder strips. Acetylation did, however, protect CCK-8 from N-terminal degradation by soluble peptidases that eluted from gallbladder and other smooth muscle tissues of the cat. Unmodified CCK-8 was degraded rapidly in the presence of these tissues and in buffers previously exposed to the same tissues. In contrast, the Ac-CCK-8 was resistant to N-terminal degradation under the same conditions. Degradation of CCK-8 from its N-terminus produces biologically inactive derivatives and could adversely affect in vitro studies. Since the acetylated-CCK-8 retained full biological and immunological activity, its use would eliminate the effect of extracellular proteolysis on CCK-8 action.