TY - JOUR T1 - The Relationship between Cation-Induced Substrate Configuration and Enzymatic Activity of Phosphatidate Phosphohydrolase from Human Liver TT - JF - انستیتو-پاستور-ایران JO - انستیتو-پاستور-ایران VL - 4 IS - 1 UR - http://ibj.pasteur.ac.ir/article-1-829-en.html Y1 - 2000 SP - 13 EP - 19 KW - Phosphatidate KW - Phosphohydrolase KW - Phosphatidic acid N2 - The mechanism by which bi-and trivalent cations affect human liver phosphatidatephosphohydrolase (PAP) activity was investigated. Bivalent cations up to 1 mM increased PAP activity whereas at higher concentrations the activity of the enzyme decreased. The stimulatory concentration for trivalent cations such as Al3+ and Cr3+, however, was much lower being 2 m M and 1 m M, respectively. All cations affecting PAP activity were also able to induce phase transition of phosphatidate from lamellar (La) to inverted hexagonal (HII) form. The rate of La-HII transition was different for each cation. At 100 mM concentration of Mg2+ only 26% of the original phosphatidate remained in La form and for other cations tested ranged from 14.5% to 76%. The phase transition was blocked by EDTA. Magnesium from 0.8 to 1.5 mM concentration raised PAP activity (3-fold) with La form of substrate but not with the HII phase. Monovalent cations such as Na+ and K+ neither affected enzyme activity nor substrate configuration. These data suggest that cation-induced PAP activation is not as a result of cation-protein interaction, but is due to formation of a suitable substrate configuration for the enzyme catalysis during phosphatidate phase transition. It appears that the real substrate configuration for PAP activity is situated between La and HII phases. M3 ER -