480 ADVENTURES IN RADIOISOTOPE RESEARCH 



heparin. The velocity constant was calculated by making use of the 

 equation valid for mono-molecular reactions 



In^-kt, 



At 



A being the total activity of the ester present in the blood at the time t, 

 Aq at the beginning of the experiment. It follows from the fair constancy 

 shown by the velocity constant recorded in Table 2 that in the hydro- 

 lysis of the hexosemonophosphate equilibrium is far from being reached 

 in three hours. It is of interest to compare the velocity constant of the 

 hydrolysis of the labelled hexosemonophosphate which we obtained 

 under the action of enzymes present in the blood with the value 

 R0BiS0N<i> found when hydrolysing the ester by 0.1 n H2SO4 . The 

 acid was found to be much less effective in hydrolysing hexosemono- 

 phosphate than the enzymes, the value of/.' = 2.2 X 10^« min"! being 



found by him. 



In one case labelled hexosemonophosphate was added to plasma and 

 we found, after the lapse of 175 min, 23% of the ester to be decomposed, 

 thus approximately the same amount which decomposes during the 

 same time in the presence of blood corpuscles (31%). 



When labelled ester disappears we have to distinguish between two 

 possibilities, in one case the number of ester molecules actually diminishes, 

 in the other case the active phosphorus atom present in the ester mole- 

 cules is replaced through an enzymatic exchange process by a non- 

 radioactive one and no change in the number of ester molecules occurs. 

 That in the above discussed cases we have to deal with the first mentioned 

 possibility (decomposition of the ester) follows from the experiment to 

 be described. To 10 cc. plasma non- active hexosemonophosphate con- 

 taining 0.15 mgm P and radioactive sodium phosphate of negligible 

 weight was added and after the lapse of 170 min the activity of the 

 plasma esters determined. If the loss of activity by the active ester 

 in the experiments recorded in Table 3 should be due to an exchange 

 process we would have to expect about 5% of the activity of the sodium 

 posphate to be incorporated in the originally non- active hexosemono- 

 phosphate added to the plasma. The result of our experiment, however, 

 has shown that the activity of the added hexosemonophosphate isolated 

 together with the other minute amounts of esters present in the plasma 

 amounted to less than Vio of the calculated activity. We have therefore 

 to conclude that at least 90% of the activity loss of the labelled hexose- 

 monophosphate recorded on Table 3 is actually due to decomposition 

 and not to an exchange process. 



<i> R. ROBISON, Biochem. J. 27, 2191 (1932). 



