Genetic Analysis of 17 Children with Hunter Syndrome:Identification and Functional Characterization of Four Novel Mutations in the Iduronate-2-Sulfatase Gene

Mucopolysaccharidosis type II （MPS II） is a rare X-linked disorder caused by alterations in the iduronate-2-sulfatase （IDS） gene. In this study, IDS activity in peripheral mononuclear blood monocytes （PMBCs） was measured with a fluorimetric enzyme assay. Urinary glycosaminoglycans （GAGs） were quantified using a colorimetric assay. All IDS exons and intronic flanks were bidirectionally sequenced. A total of 15 mutations （all exonic region） were found in 17 MPS II patients. In this cohort of MPS II patients, all alterations in the IDS gene were caused by point nucleotide substitutions or small deletions. Mutations p.Arg88His and p.Arg172＊ occurred twice. All mu- tations were inherited except for p.Gly489Alafs＊7, a germline mutation. We found four new mutations （p.Ser142Phe, p.Arg233Gly, p.Glu430＊, and p.Ile360Tyrfs＊31）. In Epstein-Barr virus （EBV）-immortalized PMBCs derived from the MPS II patients, no IDS protein was detected in case of the p.Ser142Phe and p.Ile360Tyrfs＊31 mutants. For p.Arg233Gly and p.Glu430＊, we observed a residual expression of IDS. The p.Arg233Gly and p.Glu430＊ mutants had a residuary enzymatic activity that was lowered by 14.3 and 76-fold, respectively, compared with healthy controls. This observation may help explain the mild disease phenotype in MPS II patients who had these two mutations whereas the p.Ser142Phe and p.Ile360Tyrfs＊31 mutations caused the severe disease manifestation.     

Tomato vesicles as a model system for studying in situ activity of 1-aminocyclopropane-1-carboxylic acid oxidase

A model system is described which could be used for the studyof ACC oxidase in vivo. The enzyme is localized within sedimentablevesicles isolated from the locular tissue of ripening tomatofruit. These vesicles display linear ACC oxidase activity overa period of at least 3 h and this activity is not dependenton the essential cofactors (Fe²⁺ and ascorbate) needed for theenzyme in vitro. This system has been used to demonstrate thepresence of an inhibitors) of ACC oxidase activity in the locularjuice and also to study the effects of ionophores and uncouplerson the in vivo enzyme activity. Key words: ACC oxidase, tomato, Lycopersicon esculentum