ON THE QUANTITATIVE RELATIONSHIP BETWEEN CALCIUM AND PROTHROMBIN

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Abstract
By means of a resin known as Amberlite I. R. 100, Ca was removed directly from blood without causing any other demonstrable alteration. The minimum amt. of CaCl2 that had to be readded to the plasma thus obtained to produce the shortest prothrombin time was detd. It was found to be 0.0012 M for human and 0.0004 M for dog plasma. Higher concns. of Ca had no further effect until a soln. greater than 0.02 M was added when a depressing effect was noted. Neither component A or B of prothrombin appear to influence this critical concn. of Ca for optimal prothrombin time. It is conjectured that the Ca requirement is a measure of a co-factor which with Ca and thromboplastin constitutes the activator of prothrombin. After feeding dicumarol to dogs, the minimum or critical concn. of Ca for optimum prothrombin activity increased as the prothrombin diminished. When the prothrombin time was prolonged beyond 20 secs., the normal concn. of the Ca in the blood was found no longer sufficient for optimum prothrombin activity. The range of the Ca concn. in which the minimum prothrombin time is obtained is similar for plasma decalcified by Amberlite and for oxalated plasma, but is much more narrow for citrated plasma and becomes prolonged immediately when the citrate concn. approaches stoichiometrically that of the ionized Ca. This behavior is explained by the immediate removal of Ca ions by Na citrate in contrast to the relatively slow formation of insoluble Ca oxalate.

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