Abstract
A radioimmunoassay for porcine intestinal calcium-binding protein (CaBP) has been developed. 125I-labeled CaBP was prepared using chloramine-T. Antisera to porcine CaBP were raised in guinea pigs and rabbits. Antibody-bound CaBP was separated from free CaBP using talc. The immunoassay was highly sensitive, measuring concentrations of CaBP in duodenal extracts as low as 1 ng/ml with good reproducibility. This is sufficiently sensitive to measure CaBP in small amounts of duodenal tissue obtained by peroral capsule biopsy. The method was specific for CaBP, showing no reactivity toward other duodenal proteins or several peptide hormones. Measurements of CaBP by immunoassay showed a good correlation with measurements of CaBP-specific calcium-binding. The immunodilution curves obtained when assaying pig renal cortical extracts against pure duodenal CaBP were parallel when tested with six different antisera, demonstrating a high degree of immunochemical similarity between kidney and duodenal CaBP. Clearly, the radioimmunoassay possesses distinct advantages for the study of the biologic role of CaBP.
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