Measurement and characterisation of human cholecystokinin-like immunoreactivity (CCK-LI) in tissues by radioimmunoassay.
Two radioimmunoassays specific for cholecystokinin-like immunoreactivity (CCK-LI) in human tissue are described. The first assay employed an antiserum (Z-69) directed to the sulphated tyrosine at the C-terminal end of CCK-33 and measured all biologically active molecular forms of CCK except the controversial C-terminal tetrapeptide amide (CCK4). The sensitivity of this assay was 0.6 pmol/g. A second assay (employing antiserum Z-91) measured CCK-LI forms larger than the octapeptide and had a sensitivity of 0.2 pmol/g. Both assays were characterised with endogenous human peptides. Acid (pH 2.5) and neutral extracts (pH 6.5) of human intestine and brain were assessed for CCK-LI concentrations and gel chromatography performed in the presence of 6 mol/l urea to elucidate the various molecular forms. Human cerebral cortex CCK-LI was almost all sulphated CCK-8, but large molecular mass forms were present, particularly in acid extracts, forming about 10% of the whole. Human duodenum and jejunum contained approximately equal amounts of large CCK, CCK 33/39 and of CCK-8. Both intestine and brain possess not yet isolated sulphated molecular forms which eluted between the pure CCK-8 and CCK-33/39 standards. The results obtained from this study indicate that the biosynthesis of CCK in human brain and gut is quantitatively different.
D001923:Brain Chemistry; D002766:Cholecystokinin / Q000032:analysis*; D002850:Chromatography, Gel; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007422:Intestines / Q000032:analysis; D007457:Iodine Radioisotopes; D010446:Peptide Fragments / Q000302:isolation & purification; D011863:Radioimmunoassay
D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D002766:Cholecystokinin