On the identification of two beta-D-mannosidase forms in human kidney and urine

Lysosomal beta-D-mannosidase (EC 3.2.1.25) is a low-abundance glycohydrolase whose human deficiency has been lately repor.ted. It has been partially purified and incompletely characterized from Nubian goat and guinea pig. In humans, limited studies have been performed on placental enzyme. This is the first report of the identification of two isoenzymatic forms of beta-D-mannosidase from human urine. These two forms are also found in kidney. The use of DE-52 chromatographic support allowed the separation of these two forrns (A and B) in various proportions according to their origin. In urine, the A form represented 88% of the total beta-D-mannosidase activity while in kidney, the B form represented 95% of the total activity. A and B forms, whatever their origin, showed similar physico-chemical properties (Km, optimum pH and pl). After gel filtration on Ultrogel AcA 34 column, the B forms exhibited higher molecular mass (78 kDa) than the A forms (55 kDa) and gel filtration after urea treatment suggested an oligomeric structure for these enzymes. Although the origin of the urinary A form has not yet been elucidated, a better knowledge of structure and properties is required in order to solve the relation.ship between the two forms. Moreover , in order to improve a potential diagnostic value of quantitative variations of these two forms in kidney damage further studies are in progress.