Effect of CuCl 2 , NaCl and EDTA on the enzyme a-l-iduronidase in the plasma of normal individuals and heterozygotes for MPS I Jovana Mandelli a,b , Alessandro Wajner a,b , Ricardo Pires b , Roberto Giugliani b,c , Janice C. Coelho a,b, * a Department of Biochemistry, ICBS, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil b Service of Medical Genetics, Hospital de Porto Alegre, Rua Ramiro Barcelos, 2350 sala 2243, 90035-003 Porto Alegre, RS, Brazil c Department of Genetics, IB, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil Received 30 August 2001; received in revised form 26 November 2001; accepted 3 December 2001 Abstract Background: It has been previously demonstrated that the enzyme a-L-iduronidase (IDUA) of patients with MPS I shows a different biochemical behavior in each of the three clinical forms of these. In heterozygotes, its biochemical behavior has been recently established in leukocyte and plasma samples, demonstrating that it is possible to distinguish individuals heterozygous for MPS I within an unselected population. Methods: We evaluated the effect of copper chloride, EDTA and sodium chloride on the activity of the enzyme a-L-iduronidase in the plasma of normal individuals and of MPS I heterozygotes and observed the type of inhibition caused, the Ki, the apparent Km and the apparent Vmax for each inhibitor. Results: Sodium chloride inhibited the enzyme in normal individuals and in 40% of the heterozygotes evaluated and activated it in 60% of heterozygotes. The remaining compounds inhibited IDUA in both heterozygotes and normal individuals. Conclusions: We detected significant differences capable of differentiating MPS I heterozygotes from normal individuals by simply adding sodium chloride, EDTA or copper chloride to the incubation medium at the time of IDUA activity determination, with a potential use in carrier detection protocols. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Mucopolysaccharidosis; Alpha-iduronidase; Heterozygotes 1. Introduction Type I mucopolysaccharidosis (MPS I), McKusick 25280 is a metabolic disorder inherited in a recessive autosomal mode. This disease is caused by deficiency of the lysosomal hydrolase a-L-iduronidase (IDUA, E.C.3.2.1.76), which degrades the glycosaminogly- cans (GAGs) dermatan and heparan sulfate [1,2]. By being only partially degraded, the GAGs are partially eliminated in the urine and accumulate in the lyso- somes, causing a progressive deterioration of cells, tissues and organs [1,2]. 0009-8981/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0009-8981(01)00811-7 Abbreviations: MPS I, mucopolysaccharidosis type I; H, Hurler syndrome; S, Scheie syndrome; H/S, Hurler/Scheie syndrome; IDUA, a-L-iduronidase; GAGs, glycosaminoglicans; Vmax, max- imum velocity. * Corresponding author. Servic ßo de Gene ´tica Me ´dica, Hospital de Clı ´nicas de Porto Alegre, Rua Ramiro Barcelos, 2350 90035- 003, Porto Alegre, RS, Brazil. Tel.: +55-51-33168011; fax: +55-51- 33168010/+55-51-33165535. E-mail address: jcoelho@hcpa.ufrgs.br (J.C. Coelho). www.elsevier.com/locate/clinchim Clinica Chimica Acta 318 (2002) 83 – 89