Lysosomal‘acid’ hydrolases in normal individuals controls and patients with inborn errors of metabolism

Abstract

Using commercially available artificial substrates, a number of lysosomal‘acid’ hydrolases in plasma, leucocytes and cultured skin fibroblasts from normal individuals, controls and patients with inborn errors of metabolism affecting lysosomal enzymes have been investigated. The pH optima, Km values and temperature‐activity profiles are reported, but some of the physiochemical parameters of the catalytic properties of the normal enzymes are not those that would be expected for mammalian system. Temperature optima of α‐L‐fucosidase, α‐L‐iduronidase, sphingomyelinase and β‐D‐glucuronidase were different in different sources and differences were seen in different enzymes from the same source. Only sphingomyelinase in leucocytes and α‐L‐iduronidase in leucocytes and fibro‐blasts showed maximum activity at 37°C, with other enzymes showing an unusually high optimum of 50°C or greater. Lysosomal enzymes from patients with inborn errors of metabolism showed maximum activity at the same temperature as observed in normal individuals with the exception of α‐L‐fucosidase, β‐D‐glucuronidase and α‐N‐acetyle‐D‐glucosaminidase in plasma from a patient with mucolipidosis II and β‐D‐glucuronidase in plasma from a patient with mucopolysaccharidosis type IIIA.