title: Human alpha-L-iduronidase. II. Comparative biochemical and immunologic properties of the purified low and high uptake forms.
abstract: The physicokinetic and immunologic properties of the purified low and high uptake forms of the human lysosomal hydrolase, alpha-L-iduronidase, have been determined and compared. The apparent Km and Vmax values for the low and high uptake forms were similar toward two artificial substrates, 4-methylumbelliferyl-alpha-L-iduronide (0.07 and 0.06 mmol/l; 16.15 and 14.85 mumol/min/mg, respectively), and phenyl-alpha-L-iduronide (1.42 and 1.66 mmol/l; 0.83 and 1.05 mumol/min/mg, respectively), and one natural substrate, anhydro-[3H]-mannitol-iduronide (0.86 and 1.04 mmol/l; 2.50 and 2.79 mumol/min/mg, respectively). The pH optima for both purified forms also were similar for each of the three substrates ( approximately 3.50, approximately 3.50, and approximately 4.50, respectively). Heparin markedly inhibited the 4-methylumbelliferyl-alpha-L-iduronide activities of both the low and high uptake forms, while dermatan sulfate and heparan sulfate were more inhibitory toward the low uptake activity. EDTA was a potent inhibitor of both enzyme forms; the divalent cations, Mg2+ and Ca2+, could recover up to 30% of the enzymatic activities after EDTA treatment. p-Chloromercuribenzoate and maleate also were inhibitory, whereas dithiothreitol and 2-mercaptoethanol were stimulatory. Both enzyme forms had similar thermostabilities ; the half-lives at 45, 52, and 60 degrees C were about 38, 24 and 12 min, respectively. The low and high uptake forms were immunologically cross-reactive as demonstrated by Ouchterlony double immunodiffusion and immunotitration studies using anti-human low uptake antibodies.
mesh_terms: D004705:Endocytosis; D004789:Enzyme Activation; D006025:Glycosaminoglycans / Q000494:pharmacology; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007068:Iduronidase / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D007700:Kinetics; D008168:Lung / Q000201:enzymology
chemical_list: D006025:Glycosaminoglycans; D006026:Glycoside Hydrolases; D007068:Iduronidase