Quaternary structure changes and kinetics of urease inactivation by L‐usnic acid in relation to the regulation of nutrient transfer between lichen symbionts

Abstract

Abstract L‐usnic acid inactivates urease by the formation of high molecular weight aggregates which can reach a maximum of 700,000 under experimentation conditions previously described. The substrate, urea, itself provokes temporary aggregation states which may be either active or inactive; the latter being reversible. However, these inactive aggregates, of 820,000 molecular weight, are irreversibly stabilized by L‐usnic acid. The active aggregates with molecular weights oscillating from 605,000 to 650,000, depending on whether they are formed in the presence or absence of inactivator, may combine with the substrate to form an apparently normal ES complex.