= J. L. van Rijn
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<J. L. van Rijn> is the first author of a 1984 study of how membrane composition and an accessory <protein> affect activation of <prothrombin>. The investigators varied <phospholipid> concentration and composition, with and without <factor Va>, and measured the action of <factor Xa> on bovine <prothrombin>. This tested an <enzyme> in a membrane-associated reaction system rather than assuming that its behavior in solution determines the whole process.<Kinetic studies of prothrombin activation: effect of factor Va and phospholipids on formation of the enzyme-substrate complex by J. L. van Rijn and others>[abstract, experimental variables and kinetic parameters]{ref}
For <vesicles> containing 20 mole percent <phosphatidylglycerol> and 80 mole percent <phosphatidylcholine>, the reported apparent <Michaelis constant> for <prothrombin> was 0.04 micromolar with <factor Va>, compared with 2.2 micromolar without it. The ratio is $2.2/0.04=55$. That comparison shows the scale of the change in an apparent kinetic parameter; it is not a claim that the <reaction rate> increases 55-fold at every substrate concentration. The experiment illustrates how a surface and an accessory <protein> can change the effective behavior of a biochemical reaction.<Kinetic studies of prothrombin activation: effect of factor Va and phospholipids on formation of the enzyme-substrate complex by J. L. van Rijn and others>[abstract, specified vesicle mixture and apparent Michaelis constants]{ref}
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