284 IMMUNO-CATALYSIS 



fibrinogen, and Chargaff and Bendich (1943) found that other 

 naphthoquinone derivatives were capable of clotting fibrinogen, but 

 they denied that vitamin K (2-methyl-3-phytyl-l,4-naphthoquinone) 

 had this property for the fact that two sulfonic acid derivatives 

 of naphthoquinone which have vitamin K activity, did not clot fibrino- 

 gen. The quinone group is characteristic of vitamin Ki. Lyons (1945) 

 reported that 2-methyl-l,4-naphthoquinone, which is reported to be two 

 to three times as potent as vitamin Ki, can form a gel with specifically 

 yrefared fibrinogen and that this gel is indistinguishable microscop- 

 ically from a thrombin clot. He believes that 2-methyl-l,4-naphtho- 

 quinone acts by oxidizing the thiol groups of fibrinogen prepared from 

 aged, sterile plasma which has had a preliminary treatment with 

 calcium, producing an immediate gel. 



Polarographic estimations performed at intervals during clotting 

 suggested to him that initially fresh fibrinogen (A) contains many 

 blocked protein-SH groups which are quickly converted by thrombin 

 to protein-SH. The protein-SH form of fibrinogen can be prepared 

 from aged citrated plasma, and this type of fibrinogen (B) can be im- 

 mediately converted by minute amounts of 2-methyl-l,4-naphtho- 

 quinone to form protein-S-S-protein giving a clot. The clot thus formed 

 is indistinguishable microscopically from the clot formed with throm- 

 bin, having a typical gel structure. 



Lyons believes that vitamin K is an integral and functional part of 

 the prothrombin molecule. The presence of small amounts of naphtho- 

 quinone derivative in thrombin was suggested by two color reactions 

 which were applied to a tryptic digest of thrombin (naphthoquinone 

 gives a green color with 2 : 4-dinitrophenylhydrazine and develops a 

 light blue color with ethylcyano-acetate). 



Lyons reports that both fibrinogen A and B completely lose their clot- 

 ting properties when treated with an organic mercurial (merthiolate, 

 sodium ethyl mercuri-thiosalicylate), since they block the oxidation of 

 sulfhydryl groups by combining with them. Fibrin is readily soluble in 

 sodium sulphide at pH 7.5, suggesting the presence of disulfide link- 

 ages which are disrupted by sodium sulfide, thus : 



R-S-S-Ri + 2Na2S >R-S-Na + Ri-S-Na + NasSg 



The reaction of thrombin with excess thiol compound, sodium 

 thioglycollate, was irreversible as attempts to regenerate active throm- 



