VOl. 74
280
COMMUNICATIONS T O THE EDITOR EQUILIBRIA IN THE FIBRINOGEN-FIBRIN CONVERSION'
nounced temperature dependence of this concentration was observed. This, in conjunction with Sir : experiment ( 3 ) , tends to indicate that step 3 is reIn the previous work on the clotting of fibrino- versible. gen it has been assumed or a t least implied that the ( 2 ) Both viscosity6 and flow birefringence'O rereaction is irreversible and proceeds to completion. sults point to the fact that in hexamethylene glycolSome results in this laboratory led us to believe inhibited systems the polymerized intermediate that this reaction can be treated as a reversible 4,n dissociates on dilution. This tends to support process. On the basis of information available a t the reversibility of step 2. present about the clotting process three fundamen(3) Several samples of bovine fibrinogen have tal steps have been r e c o g n i ~ e d . ~ l ~We * ~ *have ~ been clotted a t room temperature. The clots postulated that these three reactions are reversible , were removed and the supernatants placed a t involving the equilibria 37.0" for a period of 24 hours. No further clotting took place. The samples were then cooled to 2' thrombin and small but definite clots appeared after two (1) F-Q, P KI = (@)(P)/(F) hours. These clots redissolved almost completely, (2) n*=*, K? = (%)'(Q,)"' however, after 24 more hours a t 37.0' and re( 3j in@, Fibrin K3 = forrnedll again a t 2'. where F is fibrinogen, 4, is activated f i b r i n ~ g e n , ~ , ~An attempt has also been made to shift the P is fibrino-peptide,* n is a number between 5 and equilibrium in reaction 1 to the left by adding 1.7, a n is the intermediate product described by fibrino-peptide and thrombin to washed, thrombinm is a very large number, free fibrin clots suspended in buffer solutions and Ferry and Shulman,2>6 and the parentheses indicate activities of the given then measuring the concentration of soluble procomponent^.^ It is, of course, recognized that this teins in the supernatant a t equilibrium. While the reaction scheme is further complicated by the ad- precision in these measurements was not high due to sorption of the fibrino-peptide upon the fibrin experimental difficulties, nevertheless, in all cases, clot,* by the non-activating fibrinogen-fibrin- in solutions containing additional fibrino-peptide thrombin interactions described by 'Il'augh and more soluble protein material was found than in Livingstone,j and by the effects of water and pH. those with no peptide added. These experiments I t is also very probable that various polymeric tend to indicate the rcversibility of step 1 and of the reaction as a whole. intermediate products other than 4,n may exist. Quantitative work is now in progress to characThe following experiments* give evidence in supterize the postulated equilibria and to determine port of this reaction scheme. (1) Fibrin clots were washed for 24-48 hours in their respective thermodynamic parameters. a large volume of 0.3 M KC1 solution with a t least (10) H.A. Scheraga and J. K. Backus,
