Effects of Different Radioligands on the Antigen Binding Specificity of Somatostatin Antisera

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Abstract
The regions of the somatostatin (SRIF) molecule recognized by 5 antisera were systematically studied using 3 radioligands (125I-N-Tyr-SRIF, [125I-Tyr1]-SRIF and [125I-Tyr11]- and SRIF) and SRIF analogs containing sequential substitutions with Ala or Tyr. Antisera SA and moreso SB raised in sheep and N-terminal specificity when used with [125I-Tyr11]-SRIF but central molecular specificity when studied with the 2 N-terminal radiolabeled analogs. The N-terminal and central specific populations of antibodies in antiserum SB were separable by immunoaffinity adsorption using immobilized [Tyr1]-SRIF. It is of practical significance that the same antiserum (SB) could be used with different radioligands to perform N-terminal and central specific radioimmunoassays (RIA). The central specific RIA detected SRIF-14 and SRIF-28 on an approximately equimolar basis whereas the N-terminal specific RIA was selective for SRIF-14.