Volume 4, Issue 1 (1-2000)                   ibj 2000, 4(1): 13-19 | Back to browse issues page

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Haghighi B, Yari M, Tori S. The Relationship between Cation-Induced Substrate Configuration and Enzymatic Activity of Phosphatidate Phosphohydrolase from Human Liver. ibj. 2000; 4 (1) :13-19
URL: http://ibj.pasteur.ac.ir/article-1-829-en.html
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.
Type of Study: Full Length |

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