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1 CURE: Digestive Diseases Research Center, Greater Los Angeles Department of Veterans Affairs Health Care System, Los Angeles 90073; Digestive Diseases Division, University of California, Los Angeles, School of Medicine, Los Angeles, California 90024; 2 Kansas City Department of Veterans Affairs Medical Center, Kansas City, Missouri 64128; Department of Biochemistry, Kansas University Medical Center, Kansas City, Kansas 66160; and 3 Division of Immunology, Beckman Research Institute, The City of Hope Research Institute, Duarte, California 91010
Posttranslational
processing of preprosecretin generates several COOH-terminally extended
forms of secretin and
-carboxyl amidated secretin. We used synthetic
canine secretin analogs with COOH-terminal -amide, -Gly, or
-Gly-Lys-Arg to examine the effects of COOH-terminal extensions of
secretin on bioactivity and detection in RIA. Synthetic products were
purified by reverse-phase and ion-exchange HPLC and characterized by
reverse-phase isocratic HPLC and amino acid, sequence, and mass
spectral analyses. Secretin and secretin-Gly were noted to coelute
during reverse-phase HPLC. In RIA using eight different antisera raised
against amidated secretin, COOH-terminally extended secretins had
little or no cross-reactivity. Bioactivity was assessed by measuring
pancreatic responses in anesthetized rats. Amidated canine and porcine
secretins were equipotent. Secretin-Gly and secretin-Gly-Lys-Arg had
potencies of 81 ± 9% (P > 0.05)
and 176 ± 13% (P < 0.01),
respectively, compared with amidated secretin, and the response to
secretin-Gly-Lys-Arg lasted significantly longer. These data
demonstrate that 1) amidated secretin and secretin-Gly are not separable under some chromatographic conditions, 2) current RIA may not
detect bioactive COOH-terminally extended forms of secretin in tissue
extracts or blood, and 3) the
secretin receptor mediating stimulation of pancreatic secretion recognizes both amidated and COOH-terminally extended secretins.
posttranslational processing; amidation; radioimmunoassay; physiology
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