WHEAT-GERM AGGLUTININ INHIBITS BASAL-ADENYLATE AND STIMULATED-ADENYLATE CYCLASE ACTIVITY AS WELL AS BINDING OF [H-3] CERULEIN TO RAT PANCREATIC PLASMA-MEMBRANES

  • 1 January 1977
    • journal article
    • research article
    • Vol. 3  (3) , 177-187
Abstract
Wheat germ agglutinin but not concanavalin A or soybean lectin, inhibited the basal- and stimulated-adenylate cyclase activity which was present in a plasma membrane preparation from the rat pancreas. The inhibition by wheat germ agglutinin was rapid and sustained. It was of the non-competitive type and never exceeded 20% for Gpp(NH)p- and NaF-stimulated adenylate cyclase activity. The inhibition of secretin-stimulated activity was non-competitive but more pronounced (57% inhibition at a wheat germ agglutinin concentration of 20 .mu.g/ml). For the C-terminal octapeptide of cholecystokinin-pancreozymin (OC-PZ)-stimulated cyclase, the inhibition amounted to 68% and was of a mixed type (both competitive and non-competitive). This last observation might be explained by the competitive inhibition exerted by wheat germ agglutinin on the binding of peptides of the OC-PZ family to their membrane specific receptors. The various inhibitory effects of wheat germ agglutinin were completely suppressed by incubating the membranes in the presence of ovomucoid, a N-acetyl-D-glucosamine rich glycoprotein. The possible functional implication of these results is discussed. Rat pancreatic plasma membranes possess an adenylate cyclase system which can be activated by NaF, guanyl nucleotides and by gastrointestinal hormones including: secretin, vasoactive intestinal peptide, cholecystokinin-pancreozymin (CCK-PZ) and certain analogs of CCK-PZ.

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