Thermophiles are heat-loving organisms that grow at an average temperature of 323 K and to a maximum of 343 K or greater. These ancient organisms have been found to prefer the extreme conditions that were typical of the incipient earth. Researchers believe that the study of these organisms will provide details pertaining to the origin of life on earth (Guilio, 2003
). Most thermophiles that live in geothermal environments are strict anaerobes. Exceptions include the Thermus
species, especially T. thermophilus
, which are aerobic chemoorganotrophs (Ramírez-Arcos et al.
). T. thermophilus
HB8, however, has been found to grow anaerobically in the presence of nitrate. Proteins from thermophilic organisms typically remain active without denaturation even at high temperatures.
In recent years there has been an intense focus on the study of proteins present in T. thermophilus
, as similar proteins have been found to occur in certain mesophilic organisms. Many new enzymes of potential interest for biotechnological applications have been found in T. thermophilus
. These include various proteases and key enzymes for other fundamental biological processes such as DNA replication, DNA repair and RNA maturation (Pantazaki et al.
). Taq polymerase from the same genus is extensively used in the polymerase chain reaction (PCR). Glucose dehydrogenase (GDH; EC 126.96.36.199) is an enzyme found in T. thermophilus
that catalyses the oxidation of d
-glucose without prior phosphorylation to d
-β-gluconolactone using NAD or NADP as a coenzyme (Pauly & Pfleiderer, 1975
). The opportunistic uptake of glucose and galactose by T. thermophilus
GDH suggests that it represents an early state of the evolution of GDH enzymes in hyperthermophilic species (Schafer, 1996
; Albers et al.
; Theodossis et al.
). The purpose of the work reported in this paper is to generate a better understanding of the structural features that are responsible for the catalytic activity of GDH.