title: Effect of divalent cations on the limited proteolysis of prothrombin by thrombin.
abstract: The inhibitory influence of divalent cations on the ability of bovine alpha-thrombin to hydrolyze prothrombin showed the trend Mn2+ much greater than Ca2+ greater than or equal to Mg2+ greater than Sr2+ much greater than Ba2+. This effect was not due to an inhibition of thrombin's catalytic activity as measured by hydrolysis of a specific synthetic substrate, H-D-Phe-pipecolyl-Arg-p-nitroanilide (D-PhePipArgNA). The presence of divalent cations did not inhibit thrombic proteolysis of gamma-carboxyglutamic acid (Gla)-domainless prothrombin. Prothrombin and Gla-domainless prothrombin were used as competitive inhibitors in the thrombic hydrolysis of D-PhePipArgNA. The apparent Ki value calculated for prothrombin was 18 microM. When either Ca2+ or Mn2+ were present, there was no inhibition. The apparent Ki value determined for Gla-domainless prothrombin was 28 microM in either the absence or presence of Ca2+. Addition of divalent cations to prothrombin, but not to Gla-domainless prothrombin, resulted in an altered protein conformation as measured by high-performance size-exclusion chromatography and ultraviolet difference spectroscopy. These results suggest that a conformational change secondary to the interaction of divalent cations with the Gla-containing domain of prothrombin is required for cation-dependent inhibition of thrombin hydrolysis.
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D002417:Cattle; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D011516:Prothrombin / Q000378:metabolism*; D013324:Strontium / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D001464:Barium; D008345:Manganese; D011516:Prothrombin; D013917:Thrombin; D008274:Magnesium; D002118:Calcium; D013324:Strontium