Thiolester substrates for transamidating enzymes: studies on fibrinoligase.

Esters of thiocholine were shown to inhibit the crosslinking of fibrin clots by the transamidating enzyme, fibrinoligase (thrombin-activated fibrin-stabilizing factor or activated Factor XIII). Inhibition depended on the nature of the acylating group with the phenylpropionyl, phenylbutyryl, and trans-cinnamoyl esters being most effective of the compounds tested so far. Use of the thiolesters made it possible for the first time to study the reactions of fibrinoligase in fully synthetic substrate systems. Enzyme-catalyzed acyl-group transfers from the thiol-esters to a fluorescent amine [N-(5-aminopentyl) - 5 - dimethylamino - 1 - naphthalenesulfonamide] could be readily demonstrated and measured.Trans-cinnamoylthiocholine reacted with fibrinoligase in a totally calcium-dependent manner in the absence of any added amine, thus providing the first evidence for an esterolytic pathway for this enzyme. Spectral qualities, as well as appreciable extent of solubility in water, would seem to make trans-cinnamoylthiocholine a specially suitable substrate for further studies.