Purification and properties of feline and human arylsulfatase B isozymes. Evidence for feline homodimeric and human monomeric structures

Normal feline and human arylsulfatase B isozymes were purified to homogeniety from liver. The specific activities of the feline and human enzymes toward p-nitrocatechol sulfate were 1,100,000 and 800,000 units/mg of protein, and toward UDP-N-acetylgalactosamine-4-sulfate were 5,500 and 4,000 units/mg of protein, respectively. Although both enzymes had the same pH optimum (5.7), the feline enzyme was more electronegative than the human enzyme when electrophoresed on polyacrylamide gels. Compared to the human isozyme, feline arylsulfatase B had a lower K(m) toward p-nitrocatechol sulfate (1.2 versus 3.6 mM), was more thermostable at 60°C (68 versus 30 min), and had a slightly lower pI (7.8 versus 8.0). The native molecular weight of the feline enzyme was estimated to be about twice that of the human isozyme by gel filtration, analytical polyacrylamide gel electrophoresis and sucrose density-gradient centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed single protein bands of M(r)=41,000 and 38,000 for the feline and human isozymes, respectively. Alkylation and cross-linking experiments were consistent with the feline enzyme being a homodimer and the human enzyme a monomer. Amino acid compositional analyses revealed few significant differences between the two isozymes.