Isolation and characteristics of hexosaminidase A and activator protein from human kidney

: Hexosaminidase A (HA) was isolated from human kidney and purified to an electrophoretically homogeneous state. The purification procedure included ion-exchange chromatography on DEAE-cellulose, gel filtration on Toyopearl HW-55 and chromatofocusing on PBE 94 (enzyme yield 26.6%, 1133.6-fold purification). The physico-chemical and kinetic properties of HA are as follows: Mr of the purified enzyme is approximately 100,000; Km for 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside is 0.6 mM; pH optimum is at pH 4.4-4.6; pI is 5.0. The amino acid composition of the purified enzyme was determined. A specific anti-HA antiserum was raised, which did not immunoprecipitate with fibroblast extracts characterized by a mutational blockade of HA synthesis. GM2 was isolated and purified from murine liver as well as from the brain of a female patient who died of Tay-Sachs disease. The label was introduced by way of treatment of GM2 with tritiated acetic anhydride. The specific radioactivity of [3H]GM2 was 521 and 2065 Ci/M, respectively. The label was introduced into the N-acetylneuraminic acid and GalNAc residues of these GM2 preparations. An activator protein capable of solubilizing the natural substrate of HA was isolated from human kidney and partially purified (with a 19.9% yield and 480-fold purification). The Mr of the purified activator protein was approximately 21,000. Purified HA hydrolyzed [3H]GM2 only in the presence of the activator protein. An addition of the activator to the incubation medium containing normal fibroblast culture extracts and [3H]GM2 caused an increase in the rate of substrate hydrolysis, tenfold, on the average.