Distribution and characterization of neurosteroid sulfatase from the bovine brain

We investigated the regional and subcellular distribution of neurosteroid sulfatase (NSS) in the bovine brain and its enzymatic properties by using dehydroepiandrosterone sulfate (DHEA-S) as a substrate. Bovine NSS was highly concentrated in the region of the midbrain and in the hypothalamus. The enzyme was found to be a microsomal enzyme. The optimal temperature of the enzyme was 50 degrees C, which was slightly lower than that of other steroid sulfatases. The optimal pH of bovine NSS was 7.4 with a second optimum at pH 4.0. The second optimal pH of 4.0 was the most characteristic property of bovine NSS. Employing DHEA-S as the substrate, apparent Km and Vmax values were 113 +/- 21 microM and 4.1 +/- 0.4 nmol/mg protein/h, respectively, whereas Km and Vmax values were found to be 1.6 +/- 0.2 M and 1.9 +/- 0.3 micromol/mg protein/h with p-nitrophenyl sulfate (NP-S) as the substrate. NSS has thus been shown to have a higher affinity for the steroid sulfate than the phenolic compound. When DHEA-S was used as the substrate, pregnenolone sulfate (Preg-S) was a competitive inhibitor with an apparent Ki value of 46 microM, and NP-S was a non-competitive inhibitor (apparent Ki=12 mM).