Modification of the intramolecular turnover of terminal carbohydrates of dipeptidylaminopeptidase IV isolated from rat‐liver plasma membrane during liver regeneration

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Abstract
An intramolecular turnover of the terminal carbohydrates l‐fucose, N‐acetylneuraminic acid and d‐galactose is a characteristic property of several liver plasma membrane glycoproteins, first demonstrated for dipeptidylaminopeptidase IV (EC 3.4.14.5., DPP IV). The core carbohydrates d‐mannose and N‐acetyl‐d‐glucosamine turn over like the polypeptide chain. The ratio of apparent half‐lives of l‐fucose and l‐methionine of DPP IV is shifted from 0.17 in normal liver to 0.60 in regenerating liver. The ratio of half‐lives of N‐acetylneuraminic acid and l‐methionine is only slightly changed from 0.43 in normal liver to 0.61 in regenerating liver. The ratio of apparent half‐lives of d‐mannose and l‐methionine amounts to 0.80 in normal liver and 0.71 after partial hepatectomy. From this a drastic reduction of the intramolecular turnover of l‐fucose on plasma membrane DPP IV in regenerating liver can be derived. The intramolecular N‐acetylneuraminic acid turnover is affected to only a minor extent. d‐Mannose turns over like the polypeptide in both normal and regenerating liver. The intramolecular l‐fucose turnover may be involved in membrane glycoprotein recycling, which presumably is altered in regenerating liver. Additionally, l‐fucose could regulate the rate of degradation of DPP IV, since core‐fucosylated glycoproteins appear to be resistant to mammalian endo‐N‐acetylglucosaminidase.