Biological catalysts (enzymes) speed up reactions by many orders of magnitude using fundamental physical processes to increase chemical reactivity. Hydrogen tunnelling has increasingly been found to contribute to enzyme reactions at room temperature. Tunnelling is the phenomenon by which a particle transfers through a reaction barrier as a result of its wave-like property. In reactions involving small molecules, the relative importance of tunnelling increases as the temperature is reduced. We have now investigated whether hydrogen tunnelling occurs at elevated temperatures in a biological system that functions physiologically under such conditions. Using a thermophilic alcohol dehydrogenase (ADH), we find that hydrogen tunnelling makes a significant contribution at 65 degrees C; this is analogous to previous findings with mesophilic ADH at 25 degrees C. Contrary to predictions for tunnelling through a rigid barrier, the tunnelling with the thermophilic ADH decreases at and below room temperature. These findings provide experimental evidence for a role of thermally excited enzyme fluctuations in modulating enzyme-catalysed bond cleavage.
Three different phenol oxidases produced by the basidiomycete fungus Pleurotus ostreatus have been isolated and their main structural, enzymatic and physico-chemical properties characterized. Studies have focused on the most abundantly secreted of these proteins, a copper-enzyme specific towards ortho-diphenol substrates. This protein was purified to homogeneity and part of its primary structure determined by direct protein sequencing. The influence of pH, temperature and presence of water-soluble or water-insoluble organic solvents on the activity and stability of the enzyme were also investigated. These data can be used for applying bioreactors to problems of environmental concern such as waste-water treatment.
Oxidative enzymes (laccases and peroxidases) isolated from the culture media of different fungi are involved in the basic mechanism of ligninolysis via radical intermediates. However, experiments aimed at reproducing natural biodegradation in vitro have been unsuccessful so far since the single biocatalysts alone are not able to solubilize lignins because of the simultaneous recondensation of these intermediates. FAD oxidases can prevent this side reaction in lignin depolymerization by reducing quinonoids and radical compounds. This study investigates the possible role of a laccase and a FAD-dependent aryl alcohol oxidase (veratryl alcohol oxidase, VAO) excreted by the basidiomycete Pleurotus ostreatus. In fact, we found that VAO is able to reduce synthetic quinones, laccase-generated quinonoids, and phenoxy radicals with concomitant oxidation of veratryl alcohol to veratryl aldehyde. This cooperative action of laccase and VAO also prevented the polymerization of phenolic compounds and reduced the molecular weight of soluble lignosulfonates to a significant extent.
A member of the laccase Iiiultigeiie family in Pletirotins o.rtrecrlus has been cloned and sequenced. The gene structurc has been determined by coinparison with the corresponding cDNA, synthcsizcd by rcverse transcription/PCK amplification.The gene encode a laccase isoenzymc of 533 amino acids which has already been purified and characterized IPalmieri, G., Giardinii, P., Marzullo, L., Desiderio, B., Nitti, G., Cannio, R. & Sannia, G. (1993) AppI. Micmbiol. Biotcdanol. 39, 632-6363. More than 92 % of thc protein sequencc, including the N and C termini, has been verified by fast-atom-bornbardmcnl inass spectrometry, thus confirming the correspondence betwccn the gene and its protein product.The protein was N-glycosylated at Asn444. Glycan analysis showed thc presence of only a highmannosc structure containing varying numbers of mannose residucs. The presence of 0-linked oligosaccharides as well as other post-translational modification could be rulcd out by the miss analysis.
A DNA binding protein, BldR, was identified in the crenarchaeon Sulfolobus solfataricus as a protein 5-to 10-fold more abundant in cells grown in the presence of toxic aldehydes; it binds to regulatory sequences located upstream of an alcohol dehydrogenase gene (Sso2536). BldR is homologous to bacterial representatives of the MarR (multiple antibiotic resistance) family of transcriptional regulators that mediate response to multiple environmental stresses. Transcriptional analysis revealed that the bldR gene was transcribed in a bicistronic unit composed of the genes encoding the transcriptional regulator (Sso1352) and a putative multidrug transporter (Sso1351) upstream. By homology to bacterial counterparts, the bicistron was named the mar-like operon. The level of mar-like operon expression was found to be increased at least 10-fold in response to chemical stress by aromatic aldehydes. Under the same growth conditions, similar enhanced in vivo levels of Sso2536 gene transcript were also measured. The gene encoding BldR was expressed in E. coli, and the recombinant protein was purified to homogeneity. DNA binding assays demonstrated that the protein is indeed a transcription factor able to recognize site specifically both the Sso2536 and mar-like promoters at sites containing palindromic consensus sequences. Benzaldehyde, the substrate of ADH Ss , stimulates DNA binding of BldR at both promoters. The role of BldR in the auto-activation as well as in the regulation of the Sso2536 gene, together with results of increased operon and gene expression under conditions of exposure to aromatic aldehydes, indicates a novel coordinate regulatory mechanism in cell defense against stress by aromatic compounds.A chimeric nature of the transcription machinery with eukaryote-like basal factors and bacterium-like regulative components has been found in all members of the domain Archaea (50, 60). In fact, in most cases, homologs of bacterial regulators function in the context of the archaeal basal transcriptional apparatus, which resembles that of Eukarya (8, 26). Transcription initiation is mediated by a single RNA polymerase (RNAP) and two general transcription factors, TATA element binding protein (TBP) and transcription factor B (TFB), a homologue of the transcription factor TFIIB, which binds to the B recognition element (BRE) and determines the directionality of the transcription (7). The complex containing RNAP, TBP, and TFB is sufficient to initiate transcription in cell-free systems (31, 49), although an additional factor, transcription factor E, is required to increase transcription from some promoters (6, 29).A few homologs of eukaryal transcriptional regulators (33) and unique archaeal regulators (57) as well as non-sequencespecific DNA binding proteins (5, 30) have been investigated for their contribution to the regulation of archaeal genes.Homologs of bacterial transcriptional regulators are more common in Archaea, and representatives that have been studied experimentally include the Lrp homologs (13) that can fun...
The gene adh encoding a NAD-dependent alcohol dehydrogenase from the novel strain RC3 of Sulfolobus sp. was cloned and sequenced. Both the adh gene from Sulfolobus sp. strain RC3 and the alcohol dehydrogenase gene from Sulfolobus solfataricus (DSM 1617) were expressed at a high level in Escherichia coli, and the recombinant enzymes were purified, characterized, and compared. Only a few amino acid replacements were responsible for the different kinetic and physicochemical features investigated.
The gene (pox1) encoding a phenol oxidase from Pleurotus ostreatus, a lignin-degrading basidiomycete, was cloned and sequenced, and the corresponding pox1 cDNA was also synthesized and sequenced. The isolated gene consists of 2,592 bp, with the coding sequence being interrupted by 19 introns and flanked by an upstream region in which putative CAAT and TATA consensus sequences could be identified at positions ؊174 and ؊84, respectively. The isolation of a second cDNA (pox2 cDNA), showing 84% similarity, and of the corresponding truncated genomic clones demonstrated the existence of a multigene family coding for isoforms of laccase in P. ostreatus. PCR amplifications of specific regions on the DNA of isolated monokaryons proved that the two genes are not allelic forms. The POX1 amino acid sequence deduced was compared with those of other known laccases from different fungi.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.