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Karl-Erik Eriksson

Bio: Karl-Erik Eriksson is an academic researcher from University of Georgia. The author has contributed to research in topics: Cellulase & Cellulose. The author has an hindex of 60, co-authored 180 publications receiving 13208 citations.
Topics: Cellulase, Cellulose, Lignin, Cellobiose, Laccase


Papers
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Book
14 Mar 2012
TL;DR: The oil crisis during the 1970s turned interest towards the utilization of renewable resources and towards lignocellulosics in particular, and the commercial utilization of this technology has not progressed as rapidly as one would have desired.
Abstract: The oil crisis during the 1970s turned interest towards the utilization of renewable resources and towards lignocellulosics in particular. The 1970s were also the cradle period of biotechnology, and the years when biotechnical utilization of lignocellulosic waste from agriculture and forestry gained priori ty. This was a logical conclusion since one of nature's most important biologi cal reactions is the conversion of wood and other lignocellulosic materials to carbon dioxide, water and humic substances. However, while biotechnology in other areas like medicine and pharmacology concerned production of expen sive products on a small scale, biotechnical utilization and conversion of ligno cellulosics meant production of inexpensive products on a large scale. Biotechnical utilization of lignocellulosic materials is therefore a very difficult task, and the commercial utilization of this technology has not progressed as rapidly as one would have desired. One reason for this was the lack of basic knowledge of enzyme mechanisms involved in the degradation and conversion of wood, other lignocellulosics and their individual components. There are also risks associated with initiating a technical development before a stable platform of knowledge is available. Several of the projects started with en thusiasm have therefore suffered some loss of interest. Also contributing to this failing interest is the fact that the oil crisis at the time was not a real one. At present, nobody predicts a rapid exhaustion of the oil resources and fuel production from lignocellulosics is no longer a high priority."

1,408 citations

Journal ArticleDOI
TL;DR: The white rot fungus Pycnoporus cinnabarinus was characterized with respect to its set of extracellular phenoloxidases and a single predominant laccase and a lack of lignin- or manganese-type peroxidase make this organism an interesting model for further studies of possible alternative pathways of ligningin degradation by white rot fungi.
Abstract: The white rot fungus Pycnoporus cinnabarinus was characterized with respect to its set of extracellular phenoloxidases. Laccase was produced as the predominant extracellular phenoloxidase in conjunction with low amounts of an unusual peroxidase. Neither lignin peroxidase nor manganese peroxidase was detected. Laccase was produced constitutively during primary metabolism. Addition of the most effective inducer, 2,5-xylidine, enhanced laccase production ninefold without altering the isoenzyme pattern of the enzyme. Laccase purified to apparent homogeneity was a single polypeptide having a molecular mass of approximately 81,000 Da, as determined by calibrated gel filtration chromatography, and a carbohydrate content of 9%. The enzyme displayed an unusual behavior on isoelectric focusing gels; the activity was split into one major band (pI, 3.7) and several minor bands of decreasing intensity which appeared at regular, closely spaced intervals toward the alkaline end of the gel. Repeated electrophoresis of the major band under identical conditions produced the same pattern, suggesting that the laccase was secreted as a single acidic isoform with a pI of about 3.7 and that the multiband pattern was an artifact produced by electrophoresis. This appeared to be confirmed by N-terminal amino acid sequencing of the purified enzyme, which yielded a single sequence for the first 21 residues. Spectroscopic analysis indicated a typical laccase active site in the P. cinnabarinus enzyme since all three typical Cu(II)-type centers were identified. Substrate specificity and inhibitor studies also indicated the enzyme to be a typical fungal laccase. The N-terminal amino acid sequence of the P. cinnabarinus laccase showed close homology to the N-terminal sequences determined for laccases from Trametes versicolor, Coriolus hirsutus, and an unidentified basidiomycete, PM1. The principal features of the P. cinnabarinus enzyme system, a single predominant laccase and a lack of lignin- or manganese-type peroxidase, make this organism an interesting model for further studies of possible alternative pathways of lignin degradation by white rot fungi.

749 citations

Book ChapterDOI
TL;DR: This chapter describes the structure of wood and the main wood components, cellulose, hemicelluloses and lignins and the enzyme and enzyme mechanisms used by fungi and bacteria to modify and degrade these components are described in detail.
Abstract: One of natures most important biological processes is the degradation of lignocellulosic materials to carbon dioxide, water and humic substances. This implies possibilities to use biotechnology in the pulp and paper industry and consequently, the use of microorganisms and their enzymes to replace or supplement chemical methods is gaining interest. This chapter describes the structure of wood and the main wood components, cellulose, hemicelluloses and lignins. The enzyme and enzyme mechanisms used by fungi and bacteria to modify and degrade these components are described in detail. Techniques for how to assay for these enzyme activities are also described. The possibilities for biotechnology in the pulp and paper industry and other fiber utilizing industries based on these enzymes are discussed.

452 citations

Journal ArticleDOI
TL;DR: This is the first description of how laccase might function in a biological system for the complete depolymerization of lignin.

451 citations

Journal ArticleDOI
TL;DR: Several fungal laccases have been compared for the oxidation of a nonphenolic lignin dimer, 1-(3,4-dimethoxyphenyl)-2-(2-methOxyphenoxy)propan-1,3-diol (I), and a Phenol red, in the presence of the redox mediators 1-hydroxybenzotriazole (1-HBT) or violuric acid.
Abstract: Conventional pulp-bleaching techniques with chlorine or chlorine-based chemicals can, under certain conditions, generate chlorinated organic compounds that are toxic to the environment. The pulp and paper industry is facing an increasing pressure from environmentally concerned organizations to replace the conventional bleaching techniques with environmentally benign ones. Enzymatic bleaching methods have recently drawn much attention as being environmentally friendly. In addition to xylanase, laccase has been the most actively investigated enzyme for biobleaching of kraft pulp because laccase can be produced in large amounts at a reasonable price and use cheap oxygen as an electron acceptor. However, expensive redox mediators are still a hurdle in the implementation of laccase in pulp bleaching. Laccase (EC 1.10.3.1) belongs to a family of multi-copper oxidases that are widespread in numerous fungi, in various plant species (18), in the bacterium Azospirillum lipoferum (10), and in a dozen of studied insects (25). Laccase has various functions, including participation in lignin biosynthesis (21), plant pathogenicity (22), the degradation of plant cell walls (12, 17), insect sclerotization (3), bacterial melanization (10), and melanin-related virulence for humans (26). Chemically, all of these functions of laccases are related to oxidation of a range of aromatic substances. However, the net effect of such oxidations could be very different and even work in opposite directions. Plant laccases, for example, oxidize monolignols to form polymeric lignins, whereas laccases from white-rot fungi degrade and depolymerize lignins. In the degradation of lignin by white-rot fungi, the redox potential of the lignin-degrading enzymes has long been believed to play a crucial role because nonphenolic subunits, the most predominant lignin substructures in wood, have high redox potentials. The well-studied lignin peroxidase is able to oxidize nonphenolic aromatic compounds with very high ionization potentials such as 1,2-dimethoxybenzene (E1/2 = 1,500 mV) and veratryl alcohol (14, 20). Lignin peroxidase was thus once believed to be a key enzyme for fungal degradation of lignin, whereas laccase was believed to be less important because it could not oxidize veratryl alcohol (a typical model compound for nonphenolic lignin). The highest redox potential of a laccase reported so far does not exceed 800 mV, which is believed not to be high enough to oxidize a nonphenolic lignin structure. However, it has been demonstrated that laccase is able to oxidize some compounds (redox mediators) with a higher redox potential than laccase itself, although the mechanism by which this happens is not known (2, 7). In the presence of such redox mediators, laccase is also able to oxidize nonphenolic lignin model compounds and decrease pulp kappa number to a great extent (5, 8). Several effective redox mediators have been reported so far (2, 5, 6, 8, 13). The importance of the redox potential of laccases in the oxidation of lignin model compounds by laccase/mediator systems will be addressed here. While much effort has been devoted to search for more effective redox mediators, the laccase parameters governing lignin degradation and pulp bleaching are still not fully elucidated. In an effort to determine these parameters, we compared the ability of different laccases for the oxidation of lignin model compounds in a laccase-mediator system. More specifically, four laccases from different fungal species were purified and used to oxidize the β-O-4 dimer I (the most predominant lignin substructure) and phenol red (a phenolic lignin model compound). Laccases from the different sources were found to oxidize dimer I and phenol red at different rates. Criteria for a better laccase and more effective laccase-mediator systems for pulp bleaching have been suggested.

434 citations


Cited by
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Journal ArticleDOI
TL;DR: Simultaneous saccharification and fermentation effectively removes glucose, which is an inhibitor to cellulase activity, thus increasing the yield and rate of cellulose hydrolysis, thereby increasing the cost of ethanol production from lignocellulosic materials.

5,860 citations

Journal ArticleDOI
TL;DR: A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.
Abstract: Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

4,769 citations

Journal ArticleDOI
TL;DR: This review covers the literature published in 2014 for marine natural products, with 1116 citations referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms.

4,649 citations

Journal ArticleDOI
TL;DR: A review of various pretreatment process methods and the recent literature that has been developed can be found in this paper, where the goal of pretreatment is to make the cellulose accessible to hydrolysis for conversion to fuels.
Abstract: Biofuels produced from various lignocellulosic materials, such as wood, agricultural, or forest residues, have the potential to be a valuable substitute for, or complement to, gasoline. Many physicochemical structural and compositional factors hinder the hydrolysis of cellulose present in biomass to sugars and other organic compounds that can later be converted to fuels. The goal of pretreatment is to make the cellulose accessible to hydrolysis for conversion to fuels. Various pretreatment techniques change the physical and chemical structure of the lignocellulosic biomass and improve hydrolysis rates. During the past few years a large number of pretreatment methods have been developed, including alkali treatment, ammonia explosion, and others. Many methods have been shown to result in high sugar yields, above 90% of the theoretical yield for lignocellulosic biomasses such as woods, grasses, corn, and so on. In this review, we discuss the various pretreatment process methods and the recent literature that...

3,450 citations

Journal ArticleDOI
TL;DR: Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers.
Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.

3,241 citations