The Interrelation between High- and Low-Molecular-Weight Forms of GM1-β-Galactosidase Purified from Porcine Spleen

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Abstract
1) Two forms of acid β-galactosidase [EC 3.1.23] with different molecular weights catalyzing the hydrolysis of GM 1 -ganglioside and p -nitrophenyl-β- d -galactoside were separated and purified from porcine spleen. 2) The apparent molecular weights were 400,000–600,000 and 70,000–74,000 for the high (termed A m form) and low (termed A 1 form) molecular weight forms, respectively. 3) On examination by sodium dodecyl sulfate (SDS)/polyacrylamide gel electrophoresis, both forms of the enzyme had a common protein band of molecular weight 63,000, and the A m form showed three additional protein bands with molecular weights of 31,000, 21,000, and 20,000. 4) Both forms of the enzyme had similar catalytic functions with regard to pH-optimum, Km , substrate specificity and sensitivity to substrate analogues and other substances such as detergents, bovine serum albumin (BSA) and NaCl. 5) Both forms of the enzyme were fairly stable upon preincubation at 45°C at acidic pH (pH 4.5), but lost their activities at neutral pH (pH 7.0). 6) The A 1 form was a monomer at neutral pH (pH 7.0) and formed a dimer at acidic pH (pH 4.5). However, most of the A m form could not be converted to a dimeric form on gel filtration at acidic pH.