PMID: 2108141Apr 5, 1990Paper

Thermodynamic properties of the binding of alpha-, omega-amino acids to the isolated kringle 4 region of human plasminogen as determined by high sensitivity titration calorimetry.

The Journal of Biological Chemistry
L C Sehl, F J Castellino

Abstract

The binding of alpha-, omega-amino acids, which are important effectors of human plasminogen activation, to the isolated kringle 4 (K4) peptide region of this protein has been investigated by high sensitivity titration calorimetry. The titration curve of the heat changes accompanying binding of the widely employed ligand, epsilon-aminocaproic acid (EACA), to K4 were deconvoluted to yield the following binding characteristics: n = 0.87 +/- 0.08 mol/mol; Ka = 3.82 +/- 0.37 x 10(4) M-1; delta H = -4.50 +/- 0.22 kcal/mol; delta S = 6.01 +/- 0.7 entropy units; and delta G = 6.29 +/- 0.06 kcal/mol. Here, both delta H and delta S provide the driving force of the interaction, with both hydrogen bonds and hydrophobic interactions, the latter which may result from an induced conformational change in K4 upon ligand binding, as well as possible alterations in peptide-bound water structure, providing the stabilizing forces for complex formation. The thermodynamic binding parameters were not greatly influenced by pH between the values of 5.5 and 8.2, suggesting that titratable groups on K4 in this pH region did not influence the binding. Investigations of the binding properties of structural analogues of EACA to K4 demonstrated that definabl...Continue Reading

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