Islets-Activating Protein (IAP) in Bordetella pertussis that Potentiates Insulin Secretory Responses of Rats

Abstract

Following our previous report (Sumi, T. & Ui, M. (1975) Endocrinology 97, 352) that the injection of pertussis vaccine into rats enhanced their secretory response to various insulin secretagogues 3 to 10 days after the vaccination, purification of a factor responsible for this sustained enhancement of insulin secretion was undertaken from the culture media of Bordetella pertussis (strain Tohama, phase I). An active factor present in the supernatant of 48-h liquid cultures of B. pertussis was purified by sequential application of column chromatographies on hydroxyapatite, CM-Sepharose, concanavalin A-Sepharose and Biogel P-100. Bioassay of the active factor was carried out on the basis of enhancement of the insulin secretory response of rats to an intraperitoneal glucose load 3 days after the injection of the active factor. Roughly 20% of the active factor present in the culture medium was recovered as protein at 1300-fold purification. The purified protein, termed islets-activating protein (IAP), showed a single band on polyacrylamide gel electrophoresis and had a molecular weight of 77,000. Only one precipitation line was detected between purified IAP and anti-IAP antiserum by the double immunodiffusion technique. The purified IAP, when injected at as low a dose as 0.02 to 0.1 μg per rat, doubled the insulin secretory response of rats to glucose loading carried out 3 days later.