A method is described for measuring relative binding constants of lysine and analogs of lysine to plasminogen and plasminogen 'kringle' fragments. Plasminogen or kringle fragments adsorbed to lysine-Sepharose are eluted with increasing concentrations of lysine or other ligands, the concentration of ligand required to elute 50% of the protein being taken as a measure of the binding constant. The method is simple and is not dependent on monitoring conformational changes. We confirm earlier reports that the best ligands for the lysine binding sites of plasminogen are w-amino acids containing five or six carbons. We show further that both Glu-plasminogen (the native form with N-terminal glutamic acid) and Lys-plasminogen (a degraded form with N-terminal lysine), as well as the heavy chain fragments, kringle 4 and kringle 1 + 2 + 3, have very similar properties with regard to binding specificity for w-amino acids. For all species optimal binding is observed when the distance between the amino and carboxyl carbon is about 0.68 nm. The binding of ligands is decreased by the presence of polar atoms on the a and p positions of the carbon chain of amino acids.Arginine binds relatively weakly at the lysine site and there does not appear to be a separate arginine binding site in plasminogen.It has been known for over 20 years that amino acids such as 6-aminohexanoic acid have antifibrinolytic properties [l], one of which probably results from inhibition of the binding of plasminogen to fibrin [2]. Subsequent studies have shown that 6-aminohexanoic acid and lysine cause extensive conformational alterations in Glu-plasminogen [3,4] (and references in [4]); Deutsch and Mertz [5] utilized the strong affinity of plasminogen for lysine-Sepharose in the development of a convenient method for purification of plasminogen.

Pantrak E.K. (endpoint and kinetic) Amylase reagent (Calbiochem-Behring) is the first commercially available alpha-amylase reagent in which p-nitrophenyl-d-glycosides are used as the substrate. We describe the effect of reagent composition on reagent performance. The reagent performance compares well with that of Amylochrome reagent (Hoffmann-La Roche), Du Pont aca, and Beckman D.S. amylase reagents in assays of sera and urines. We detected no interference from increased concentrations of glucose or pyruvate in the sample. The reagent can be used in either a manual fixed-time or an automatable kinetic assay.