The physical significance of Km in the prothrombinase reaction

Marc Lee Pusey, Gary L Nelsestuen

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34 Scopus citations


Key kinetic parameters for the prothrombinase complex formed on membranes of phosphatidylserine (PS)/phosphatidylcholine (PC) ( 40 60) (Km = 0.12 μM, kcat = 11 s-1) or PS/PC ( 2 98) (Km = 0.40 μM, kcat = 11 -1) differed only slightly. In contrast, the density of proteins on the membrane surface at the Km differed greatly for the two membranes. The kinetics appeared unaffected by conditions where the number of phospholipid vesicles (2% PS) exceeded the number of protein molecules. These results establish that the Km for the prothrombinase reaction is determined by the concentration of prothrombin in solution rather than its density at the membrane surface. This system can be treated as a dissociable enzyme acting on a soluble substrate.

Original languageEnglish (US)
Pages (from-to)526-532
Number of pages7
JournalBiochemical and Biophysical Research Communications
Issue number2
StatePublished - Jul 29 1983


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