L-usnate-urease interactions: binding sites for the ligand.

L-usnic acid inactivates urease by formation of high molecular weight aggregates which can reached by a maximum of 880 000. L-cysteine partially reverses the inactivation of stimulating the appearance of active high molecular weight polymers. The existence of two class of binding points for L-usnic acid on the urease molecule is proposed, the first showing high affinity for the ligand, related with the loss of activity, and the second, of low affinity, related to polymerization process.