A bombesin immunoreactive peptide in milk.
Immunoreactivity to the amphibian peptide bombesin was found in instant nonfat dry milk (ca. 0.7 ng/ml) and in the whey of whole or skim bovine milk (ca. 1.2 ng/ml) even after ultracentrifugation. The soluble immunoreactivity was associated with a peptide exhibiting the following characteristics: (i) parallel displacement in an immunoassay using an antiserum recognizing bombesin amino acid residues 5-8; (ii) separation from both gastrin-releasing peptide and amphibian bombesin by gel filtration--the approximate Mr was 3,200; (iii) denaturation in urea, reduction by dithiothreitol, and acetylation by iodoacetamide had no effect on its elution profile by gel-filtration chromatography and the aggregation of added bombesin to milk proteins or peptides was not observed; (iv) reversed-phase HPLC separated milk immunoreactivity from gastrin-releasing peptide and bombesin; (v) digestion by trypsin yielded a smaller immunoreactive peptide fragment, whereas nearly all immunoreactivity was lost by treatment with alpha-chymotrypsin; and (vi) the level of immunoreactivity was unaffected by boiling. These data show that milk is an exogenous source of bombesin-like immunoreactivity, which may account for the increase of gastric acid and gastrointestinal hormone levels after the consumption of milk.
D000818:Animals; D001839:Bombesin / Q000276:immunology*; D002417:Cattle; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D008892:Milk / Q000032:analysis / Q000276:immunology*; D008970:Molecular Weight; D010455:Peptides / Q000032:analysis / Q000276:immunology*; D011863:Radioimmunoassay
D010455:Peptides; D001839:Bombesin