The Role of Low Molecular Weight Antifreeze Glycopeptides in the Bile and Intestinal Fluid of Antarctic Fish

Abstract

ABSTRACT The role that low molecular weight antifreeze glycopeptides play in the physiology of polar fishes has been an open question. In this study, we demonstrate that antifreeze glycopeptides are present in the bile as well as the intestinal fluid of antarctic fishes. Isolation of antifreeze glycopeptides from these fluids by DEAE ion exchange chromatography followed by polyacrylamide gel electrophoresis revealed the presence of only low molecular weight glycopeptides (6, 7 and 8). Removal of the gall bladder with subsequent occlusion of the common bile duct eliminated the transport of antifreezes into the intestine. This suggests that antifreeze glycopeptides enter the intestinal lumen by biliary secretion. Measurements of reabsorption, both in vivo and in vitro, indicate that antifreeze glycopeptides are not reabsorbed as intact molecules. Our results suggest that these glycopeptides are excreted. We conclude that low molecular weight antifreeze glycopeptides are necessary to prevent the intestinal fluid from freezing and provide the first clear evidence that low molecular weight antifreeze glycopeptides have a specific biological function in polar fishes.