title: On the Temperature Dependence of Enzyme-Catalyzed Rates.
abstract: One of the critical variables that determine the rate of any reaction is temperature. For biological systems, the effects of temperature are convoluted with myriad (and often opposing) contributions from enzyme catalysis, protein stability, and temperature-dependent regulation, for example. We have coined the phrase "macromolecular rate theory (MMRT)" to describe the temperature dependence of enzyme-catalyzed rates independent of stability or regulatory processes. Central to MMRT is the observation that enzyme-catalyzed reactions occur with significant values of ΔCp(‡) that are in general negative. That is, the heat capacity (Cp) for the enzyme-substrate complex is generally larger than the Cp for the enzyme-transition state complex. Consistent with a classical description of enzyme catalysis, a negative value for ΔCp(‡) is the result of the enzyme binding relatively weakly to the substrate and very tightly to the transition state. This observation of negative ΔCp(‡) has important implications for the temperature dependence of enzyme-catalyzed rates. Here, we lay out the fundamentals of MMRT. We present a number of hypotheses that arise directly from MMRT including a theoretical justification for the large size of enzymes and the basis for their optimum temperatures. We rationalize the behavior of psychrophilic enzymes and describe a "psychrophilic trap" which places limits on the evolution of enzymes in low temperature environments. One of the defining characteristics of biology is catalysis of chemical reactions by enzymes, and enzymes drive much of metabolism. Therefore, we also expect to see characteristics of MMRT at the level of cells, whole organisms, and even ecosystems.
authors.affiliation: School of Science, University of Waikato , Hamilton 3240, New Zealand.
authors.forename: Vickery L
authors.initials: VL
authors.lastname: Arcus
authors.affiliation: School of Science, University of Waikato , Hamilton 3240, New Zealand.
authors.forename: Erica J
authors.initials: EJ
authors.lastname: Prentice
authors.affiliation: School of Science, University of Waikato , Hamilton 3240, New Zealand.
authors.forename: Joanne K
authors.initials: JK
authors.lastname: Hobbs
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Mulholland
authors.forename: Marc W
authors.initials: MW
authors.lastname: Van der Kamp
authors.affiliation: Department of Biology and Biochemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Pudney
authors.affiliation: Biomolecular Interaction Centre and Department of Chemistry, University of Canterbury , Christchurch 8041, New Zealand.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Parker
authors.affiliation: School of Science, University of Waikato , Hamilton 3240, New Zealand.
authors.forename: Louis A
authors.initials: LA
authors.lastname: Schipper
mesh_terms: D000818:Animals; D001412:Bacillus subtilis / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D003080:Cold Temperature; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism*; D006358:Hot Temperature; D007700:Kinetics; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D004798:Enzymes