412 VITAMIN K GROUP 



from 1, or less, to as high as 2, approximately. At the lower levels, on a 

 molar basis, vitamin Ki is clearly the more efficient form of the vitamin. 

 It is probable that these compounds are so dissimilar that they cannot be 

 evaluated in terms of each other except at stated dose levels. Therefore, 

 they cannot be used interchangeably for assay standards. 



These experimental observations are in agreement with relations that 

 may be derived on the basis of certain assumptions.''^ If the relation of 

 vitamin K to prothrombin formation is expressed as follows: 



K + A-§±KA-^P (1) 



where K = any form of vitamin K. 



A = proenzyme. 

 KA = enzyme which forms prothrombin. 



C = constant. 



E = efficiency of formation of prothrombin by KA . 



P = prothrombin = KA X E. 

 Then 



_dK ^ KX A XC ^ KXAXGXE , . 



dt KA P ^ ^ 



which may be written 



d log K P 



dt A XC X E 



or integrated and simplified to eq. 3 as a practical expression of the rela- 

 tion of these factors, over a given time interval. 



log K = -, ^ (3) 



^ A XC X E 



It is recognized that within the assay range P is for practical purposes 

 equal to a constant times the reciprocal of the prothrombin-clotting time, T. 



C 



Hence 



C S 



^°^" ^ = AXCXE xY^27d ^ f ^^^ 



It appears that A, which is similar to the "apoenzyme" recently pro- 

 posed by Quick and Collentine,'^ is relatively constant in respect to the above 



" H. J. Almquist, Arch. Biocheni. and Biophys. 35, 464 (1952'). 



