Title: [24] Assaying activity and assessing thermostability of hyperthermophilic enzymes
Abstract: There is now a wide variety of intra- and extracellular enzymes available from organisms growing above 75° and having sufficient stability to allow assay well above this temperature. For some of these enzymes, to assay below even 95° will involve measurement below the optimal growth temperature for the organism. This chapter covers practical aspects of enzyme assay procedures that are specific to high temperatures. The reason that by far the commonest routine assessment of enzyme stability is activity loss, and it is always unwise to measure enzyme activity without being confident of its stability during the assay, an outline of procedures is included for measuring enzyme activity loss/stability at high temperatures. However, it should be remembered that (relatively) small changes in activity and stability can be generated separately by in vitro directed evolution if the appropriate selection pressures are applied, indicating that some changes in thermostability are not necessarily linked to changes in activity and that the observed inverse correlation of the two properties may reflect in part the process by which any enzyme has adapted.