An Unusual Oxygen-Sensitive, Iron- and Zinc-Containing Alcohol Dehydrogenase from the Hyperthermophilic Archaeon Pyrococcus furiosus
| Autor: | Michael W. W. Adams, Kesen Ma |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
Hot Temperature
Hydrogenase Iron Molecular Sequence Data Models Biological Microbiology Oxidoreductase Enzyme Stability Metalloproteins Amino Acid Sequence Amino Acids Molecular Biology Ferredoxin Alcohol dehydrogenase chemistry.chemical_classification Sequence Homology Amino Acid biology Alcohol Dehydrogenase biology.organism_classification Enzymes and Proteins Hyperthermophile Oxygen Pyrococcus furiosus Zinc Enzyme chemistry Biochemistry Fermentation biology.protein Thermococcus Sulfur |
| Zdroj: | Journal of Bacteriology. 181:1163-1170 |
| ISSN: | 1098-5530 0021-9193 |
| DOI: | 10.1128/jb.181.4.1163-1170.1999 |
| Popis: | Hyperthermophiles are a group of microorganisms that grow at temperatures of 90°C and above (1, 61–63). They are found in geothermally heated environments (62), and all but two of them are classified as members of the domain Archaea (71). The majority are anaerobic organisms, and for many of them significant growth is dependent on the reduction of elemental sulfur (S0) to H2S. Various organic compounds or molecular H2 serve as electron donors (1, 9, 56, 58). The organisms differ, however, in their dependence on S0. For example, the growth of Thermococcus strain ES-1 is obligately dependent on S0, and the amount of S0 added to the growth medium has a major effect on the activities of enzymes such as alcohol dehydrogenase (ADH), hydrogenase, and formate ferredoxin oxidoreductase (FMOR) (37). Thus, the specific activities of these enzymes are dramatically higher in cells grown under S0 limitation than in S0-sufficient cells (37), while the activities of various other catabolic enzymes are similar in the two cell types. It was therefore postulated that ADH, together with hydrogenase and FMOR, served to dispose of excess reducing equivalents when Thermococcus strain ES-1 is grown under S0 limitation and that S0, presumably via the cellular redox potential, regulated the expression of these enzymes (37). In contrast to Thermococcus strain ES-1, several hyperthermophilic species that are able to reduce S0 also grow well in its absence by a fermentative-type metabolism. One of the best studied of this class is Pyrococcus furiosus, which grows optimally at 100°C. In this case, the addition of S0 stimulates growth by an as yet unknown mechanism (20, 59). If S0 reduction affects the internal redox balance of P. furiosus, and thus the bioenergetics of fermentation, then one might expect that enzymes involved in the disposal of the reducing equivalents generated during fermentation to be affected by the presence of S0. The initial objective of the present study was, therefore, to determine to what extent, if any, the presence of S0 affects the activities of key metabolic enzymes, in particular, ADH, hydrogenase, and FMOR, in P. furiosus. Our results show that there is a fundamental difference in the response to S0 between fermentative-type hyperthermophiles, like P. furiosus, and those that appear to respire S0, such as Thermococcus strain ES-1, with regard to key metabolic enzymes such as ADH, hydrogenase, and FMOR. It was therefore of interest to determine if differences existed in the nature of these enzymes in the two types of organism. Since ADH, but not hydrogenase or FMOR, had been previously purified from Thermococcus strain ES-1 (37), we focused on characterizing the ADH from P. furiosus. We show here the P. furiosus enzyme is part of the same ADH family as that from Thermococcus strain ES-1 but differs in that it contains zinc as well as iron. The proposed physiological role of ADH in P. furiosus is to both dispose of excess reducing equivalents and to detoxify the aldehydes produced by the fermentative pathways. |
| Databáze: | OpenAIRE |
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