The assay temperature must be within the linear range,

although the enzyme possesses there not its maximum activity. From these considerations it becomes clear that a general standard temperature for all enzyme assays cannot be defined. For the majority of assays, especially for mammalian enzymes, three distinct temperatures are in use. The physiological temperature, 37 °C, matches directly the natural condition of the enzyme and, compared with the other two assay temperatures, the enzyme develops there its highest activity, i.e. the lowest enzyme Selleckchem Cabozantinib amounts are required (Figure 5A). However, this temperature is nearest to the denaturation range, and it requires efficient thermostatting. Since the assay mixture is usually stored at low temperature, a considerable time of several minutes to warm up the assay is needed. The attainment of the proper temperature should be controlled, but to save time, especially with larger test series, the experimenter may be tempted to shorten the thermostatting time and the reaction will in fact proceed with reduced activity. To save time a separate thermostatting device is recommended, where one sample can already be pre-thermostatted while measuring the actual sample. Performing the assay at room Torin 1 nmr temperature may eliminate the problem of thermostatting. Room temperature, however, is not constant; it varies not only between different laboratories, but changes also in the same room upon

opening or closing windows and doors, radiation of sunlight, or defective air conditioning. Therefore a slightly elevated temperature, 25 °C, is used. Here thermostatting is not very crucial, the accurate temperature will be attained within a short time and even insufficient thermostatting cause only slight aberrations of the results. Compared with tests at the physiological temperature, however, the activity

is evidently lower and thus significantly more enzymes is needed to obtain comparable velocities (Figure 5A). Nevertheless, due to the easier manipulation and more robust data most protocols MTMR9 suggest 25 °C as assay temperature. This is convenient for simple and routine assays as long as enough enzyme material is available, while for more thorough investigations of enzymes the physiological temperature should be preferred. The third of the frequently used temperatures, 30 °C, is a compromise between the other two. It is closer to the physiological temperature but easier to achieve, the enzyme is more active than at 25 °C, and thermal denaturation must not be feared. In special cases none of these three temperatures can be employed. Enzymes from thermophilic organisms, growing at temperatures up to and even above the boiling point of water, show very low activities at moderate temperatures and should preferentially be tested at the growth temperature of their organism (Vieille and Zeikus, 2001, Rainey and Oren, 2006 and Gerday, 2007).