1. 1. Two forms of cytosol neuraminidase (EC 188.8.131.52) (neuraminidase A and neuraminidase B) were isolated and purified from pig brain homogenate, by proceeding through the following steps: centrifugation of brain homogenate at 105 000 × g (1 h); ammonium sulphate fractionation (35-55% saturated fraction); column chromatography on Biogel A 5 m; column chromatography on hydroxy apatite/cellulose gel; affinity chromatography on Affinose-tyrosyl-p-nitrophenyloxamic acid. The separation of the two forms of neuraminidase was provided by chromatography on hydroxylapatite/cellulose gel. Neuraminidase A was purified about 500-fold; neuraminidase B about 400-fold. 2. 2. The pH optima and the maximum activities in various buffers were different for neuraminidase A and B (for instance the pH optimum was, in sodium acetate/acetic acid buffer, 4.7 for neuraminidase A and 4.9 for neuraminidase B). Ions affected in a different way the two enzymes: K+ activated neuraminidase A but not neuraminidase B; Na+ and Li+ inhibited neuraminidase A at a higher degree than neuraminidase B. Neuraminidase B seemed to be moderately activated by some bivalent cations (Ca2+; Mg2+; Zn2+); neuraminidase A did not. The Km values for sialyllactose were different: 22 · 10-3 M for neuraminidase A; 0.46 · 10-3 M for neuraminidase B.
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