Enzyme activity down to-100 degrees C

The activities of two enzymes, beef liver catalase (EC 1.11.1.6) and calf i ntestine alkaline phosphatase (EC 3.1.3.1), have been measured down to -97 degrees C and -100 degrees C, respectively. Enzyme activity has not previou sly been measured at such low temperatures. For catalase, the cryosolvents used were methanol:ethylene glycol:water (70:10:20) and DMSO:ethylene glyco l:water (60:20:20). For alkaline phosphatase, methanol:ethylene glycol:wate r (70:10:20) was used. All of the Arrhenius plots were linear over the whol e of the temperature range examined. Since the lowest temperatures at which activity was measured are well below the dynamic transition observed for p roteins, the results indicate that the motions which cease below the dynami c transition are not essential for enzyme activity. In all cases the use of cryosolvent led to substantial increases in Arrhenius activation energies, and this imposed practical limitations on the measurement of enzyme activi ty below -100 degrees C. At even lower temperatures, enzyme activity may be limited by the effect of solvent fluidity on substrate/product diffusion, but overall there is no evidence that any intrinsic enzyme property imposes a lower temperature limit for enzyme activity. (C) 2000 Elsevier Science B .V. All rights reserved.