Purification of two hexosaminidases from human kidney

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Abstract
Hexosaminidase forms A and B were isolated from human kidney in a homogeneous state as demonstrated by electrophoretic and enzymic criteria. The enzymes were stable for at least 18 months when stored at -20 degrees C in 0.025 M-phosphate buffer, pH 6.5. The molecular weights of forms A and B were estimated by gel filtration to be 111 000 +/- 1500 and 114 000 +/- 1600 respectively. The molecular weights of hexosamidase A and B subunits were determined by using polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. Hexosaminidase A dissociated into one subunit with mol.wt. 68 000. Hexosaminidase B dissociated into three subunits with mol. wts. 100 000, 68 000 and 37000 respectively, and one protein band of mol.wt. 140 000. After treatment of hexosaminidases A and B with iodoacetic acid, the molecular weights of the carboxymethylated polypeptide subunits were also estimated. Carboxymethylated hexosaminidase A dissociated into one major subunit of mol.wt. 18 000 and two other protein bands of mol.wts. 65 000 and 100 000. Carboxymethylated hexosaminidase B dissociated into one major subunit for mol.wt. 19 000 and an additional band of mol.wt. 37 000. The Km of the enzymes for the synthetic substrate p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside was 0.8 mM. Both enzymes were inhibited or activated by various metal ions. Double pH optima for the enzymes were found at pH 4.5 and 4.8.