Regulatory properties of glutamate dehydrogenase from Sulfolobus solfataricus

Extremophilic Oxidoreductases for the Industry: Five Successful Examples With Promising Projections

In a global context where the development of more environmentally conscious technologies is an urgent need, the demand for enzymes for industrial processes is on the rise. Compared to conventional chemical catalysts, the implementation of biocatalysis presents important benefits including higher selectivity, increased sustainability, reduction in operating costs and low toxicity, which translate into cleaner production processes, lower environmental impact as well as increasing the safety of the operating staff. Most of the currently available commercial enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of conditions, which limits their actual application under industrial settings. For this reason, enzymes from extremophilic microorganisms stand out for their specific characteristics, showing higher stability, activity and robustness than their mesophilic counterparts. Their unique structural adaptations allow them to resist denaturation at high temperatures and salinity, remain active at low temperatures, function at extremely acidic or alkaline pHs and high pressure, and participate in reactions in organic solvents and unconventional media. Because of the increased interest to replace chemical catalysts, the global enzymes market is continuously growing, with hydrolases being the most prominent type of enzymes, holding approximately two-third share, followed by oxidoreductases. The latter enzymes catalyze electron transfer reactions and are one of the most abundant classes of enzymes within cells. They hold a significant industrial potential, especially those from extremophiles, as their applications are multifold. In this article we aim to review the properties and potential applications of five different types of extremophilic oxidoreductases: laccases, hydrogenases, glutamate dehydrogenases (GDHs), catalases and superoxide dismutases (SODs). This selection is based on the extensive experience of our research group working with these particular enzymes, from the discovery up to the development of commercial products available for the research market.

Thermophiles and the applications of their enzymes as new biocatalysts

Ecological and efficient alternatives to industrial processes have sparked interest for using microorganisms and enzymes as biocatalysts. One of the difficulties is finding candidates capable of resisting the harsh conditions in which industrial processes usually take place. Extremophiles, microorganisms naturally found in "extreme" ecological niches, produce robust enzymes for bioprocesses and product development. Thermophiles like Geobacillus, Alyciclobacillus, Anoxybacillus, Pyrococcus and Thermoccocus are some of the extremophiles containing enzymes showing special promise for biocatalysis. Glutamate dehydrogenase used in food processes, laccases and xylanases in pulp and paper processes, nitrilases and transaminases for pharmaceutical drug synthesis and lipases present in detergents, are examples of the increasing use of enzymes for biocatalytic synthesis from thermophilic microorganisms. Some of these enzymes from thermophiles have been expressed as recombinant enzymes and are already in the market. Here we will review recent discoveries of thermophilic enzymes and their current and potential applications in industry.

Purification and characterization of a thermostable glutamate dehydrogenase from a thermophilic bacterium isolated from a sterilization drying oven

Glutamate dehydrogenase from axenic bacterial cultures of a new microorganism, called GWE1, isolated from the interior of a sterilization drying oven, was purified by anion-exchange and molecular-exclusion liquid chromatography. The apparent molecular mass of the native enzyme was 250.5 kDa and was shown to be an hexamer with similar subunits of molecular mass 40.5 kDa. For glutamate oxidation, the enzyme showed an optimal pH and temperature of 8.0 and 70 degrees C, respectively. In contrast to other glutamate dehydrogenases isolated from bacteria, the enzyme isolated in this study can use both NAD(+) and NADP(+) as electron acceptors, displaying more affinity for NADP(+) than for NAD(+). No activity was detected with NADH or NADPH, 2-oxoglutarate and ammonia. The enzyme was exceptionally thermostable, maintaining more than 70% of activity after incubating at 100(o)C for more than five hours suggesting being one of the most thermoestable enzymes reported in the family of dehydrogenases.