[Beta-D-mannosidase]

Abstract

Among the lysosomal hydrolytic enzymes, and especially the exoglycosidases which carry out the degradation of the glycan moieties of glycoconjugates, the beta-D-mannosidase (beta-MAN) was the least investigated, up to the discovery of the inherited deficiency, in 1979-1980 for the caprine disease, and in 1986 for the human one. The beta-mannosidosis is characterized by mental retardation in children and by severe osteoarticular damage in kids. In both cases occurs the storage of oligosaccharides which are later excreted in urine: beta-mannosyl (1-4)-N-acetyl-beta-glucosaminyl (1-4)-N-acetylglucosamine, and beta-mannosyl (1-4)-N-acetylglucosamine in caprine disease, but only the last disaccharide in human patients. Having previously studied the serum enzymes, we report here the results obtained in the study of human urinary and renal beta-MAN. In each case we observed the existence of two isoforms of enzyme, B and a more acidic one, A. The main properties of these forms were determined, showing that A form of either origin seems to be identical, as well as the B form. But the ratios of activity B/A are inverted: 0.2-0.3 in urine, versus 15-20 in kidney. This observation led to the examination of the urinary enzyme of patients after a kidney transplantation. The B form is the major one, with a B/A ratio of around 3. The two isoforms are respectively identical to the normal renal and urinary ones. This shows that the B isoform determination way be used as reflecting a renal tubular damage.