Modulation of alkaline phosphatases from Saccharomyces cerevisiae

Abstract

We aimed at characterizing Saccharomyces cerevisiae alkaline phosphatases (ALPs) activity modulation by ALP activity classic inhibitors, cholesterol and steroid hormones as well as at identifying catalytic similarities between yeast and mammals ALPs. Saccharomyces cerevisiae expresses two ALPs, coded for PHO8 and PHO13 genes. PHO8 product is repressible by Pi in the medium. ALP activity from yeast (either grown in low or high phosphate medium) homogenates was determined with p-nitrophenylphosphate as substrate, pH 10.4 (lPiALP or hPiALP, respectively). L-Aminoacids and levamisole activated but EDTA and vanadate inhibited hPiALP, although with different patterns of effects. L-Homoarginine and L-tryptophan had a lower activatory effect on lPiALP. Corticosterone inhibited hPiALP but had the effect cancelled by growth on low phosphate medium. Cholesterol had a significantly different effect on hPiALP and lPiALP. beta-Estradiol and progesterone effects were different on hPiALP and lPiALP, showing a concentration-dependent activation of lPiALP (especially beta-estradiol). L-Homoarginine 5 mM was the stronger activator of hPiALP. L-Homoarginine 5 mM and beta-estradiol 5 mM may be used to discriminate between lPiALP and hPiALP. Our set of results does not allow identification of similarities between the behaviour of 2 Saccharomyces cerevisiae ALPs and any of the 4 human ALPs but allow us to raise the hypothesis of in vivo differential regulation of Saccharomyces cerevisiae ALPs by L-tryptophan, L-homoarginine and beta-estradiol.