Turnover (determined by k_cat)
Many enzymes may catalyze a reaction, but with very low k_cat, too low for practical application. In such cases, improvement of turnover can be brought about by directed evolution, gene shuffling and combination of rational and combinatorial methods. The turnover may also be influenced by alterations in the micro­environment (including the type and use of immobilization and the temperature), even though such modifications often result in low k_cat.

The operating temperature of a biocatalytic process is frequently dictated by factors relating to reaction rather than the catalyst. Therefore, generally highest feasible reaction temperature is selected from an appropriate microorganism, since functionally homologous enzymes can be obtained from microbes ranging from psychotolerants (cold-active; can function at temperature as low as -10°C) to hyperthermophiles (which retain activity at a temperature as high as 100°C).