Abstract
Pyruvate kinase (EC 2.7.1.40) was partially purified from an extreme thermophile, Thermos thermophilus HB8, and its enzymatic properties were studied. The enzyme showed high thermostability and was also stable at lower temperatures. Divalent metal ions such as Co2+, Mn2+, and Mg2+ were required for activity. The enzyme showed optimum pH of 5.5_??_6.0 and sigmoidal rate curves for both substrates PEP and ADP at the growth temperature, 75°C. UDP and GDP also acted as nucleotide substrates. The enzyme was activated by the glycolytic intermediates in the following order: glucose 6-phosphate>fructose 6-phosphate>dihydroxy-acetone phosphate>glyceraldehyde 3-phosphate, fructose 1, 6-bisphosphate. The enzyme, on the contrary, was inhibited by ATP, glycerate 3-phosphate, glycerate 2-phosphate, and P1. AMP, 20 amino acids, and several intermediates of the tricarboxylic acid cycle were noneffective. The in vivo regulatory functions of the enzyme were discussed from these findings.
