Processing and transport of human small intestinal lactase‐phlorizin hydrolase (LPH)

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Abstract
The effect of glycosylation on the intracellular transport of human intestinal lactase-phlorizin hydrolase (LPH) was investigated by biosynthetic labeling of biopsy samples in the presence or absence of glycosidase inhibitors. In the presence of deoxynojirimycin (dNM) and deoxymannojirimycin (dMM), endo H sensitive LPH glycoforms of M r = 135,000 in both cases were produced (LPH dNM and LPH dMM ). The LPH glycoform generated in the presence of swainsonine had an apparent molecular mass of 141,000 (LPH Swa ) and was partially sensitive to endo H. By contrast to unmodified mature LPH (LPHm M r = 160,000), these glycoforms are either not O-glycosylated (LPH dNM and LPH dMM ) or partially O-glycosylated (LPH Swa ) indicating that processing of N-linked carbohydrates has direct effects on the O-glycosylation of pro-LPH. Analysis of transport kinetics of the various glycoforms strongly suggested that carbohydrate modification does not affect the transport of pro-LPH from the cis-Golgi to the cell surface, but could be rate limiting at the level of the ER.