THE ISOLATION FROM HUMAN SEMINAL PLASMA OF A NEW FORM OF SOLUBLE 5'-NUCLEOTIDASE

Soluble broad spectrum 5'-nucleotidase from human seminal plasma was p urified to homogeneity by a combination of (NH4)(2)SO4 precipitation, affinity chromatography, and gel filtration. The pure enzyme had a spe cific activity of 4800 nmol min(-1) mg(-1) SDS-PAGE of purified enzyme preparation revealed a single polypeptide band of 53 kDa and a tetram eric structure of 203 kDa was proposed for the native enzyme. This for m had modest preference for AMP as substrate; Mg2+ and Mn2+ were activ ators of the enzyme although its activity was not absolutely dependent on the presence of these exogenous bivalent cations. The enzyme, reco vered in the nonsedimentable fraction of human seminal plasma, had a p H optimum of 7.5; ATP and ADP were inhibitors of mixed type, P-i was a potent inhibitor at nonphysiological concentrations, and Con A and ad enosine 5-[alpha,beta-methylene]diphosphate had no effect on the enzym e activity. The enzyme described here therefore has some unique proper ties between truly cytoplasmic and membrane-bound derived forms. (C) 1 996 Academic Press, Inc.