Yoshitsugu Kosugi

Hyperthermostable Endoglucanase from Pyrococcus horikoshii

ABSTRACT An endoglucanase homolog from the hyperthermophilic archaeon Pyrococcus horikoshii was expressed in Escherichia coli, and its enzymatic characteristics were examined. The expressed protein was a hyperthermostable endoglucanase which hydrolyzes celluloses, including Avicel and carboxymethyl cellulose, as well as β-glucose oligomers. This enzyme is the first endoglucanase belonging to glycosidase family 5 found from Pyrococcus species and is also the first hyperthermostable endoglucanase to which celluloses are the best substrates. This enzyme is expected to be useful for industrial hydrolysis of cellulose at high temperatures, particularly in biopolishing of cotton products.

Synthesis of triacylglycerol from polyunsaturated fatty acid by immobilized lipase

More than 95% of polyunsaturated acid (PUFA) was converted to triacylglycerol by immobilized lipase fromCandida antarctica orRhizomucor miehei. The esterification was carried out at 50–60°C with shaking and dehydration for 24 h. The substrates consisted of glycerol and free fatty acid or ethyl esters of the fatty acid at a 1∶3 molar ratio. The docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) in the substrate polymerized during the reaction, and they required 5–10% more than the stoichiometric amount to compensate for the PUFA loss. On the contrary, ethyl esters of DHA and EPA were not polymerized. Pure tridocosahexaenoyl, trieicosapentaenoly and triarachidonoyl glycerol were isolated after passing the product through a basic aluminum oxide column. Industrial feasibility of this process was discussed for the ethyl ester as substrate.

THERMOSTABLE AMINOPEPTIDASE FROM PYROCOCCUS HORIKOSHII

From the genome sequence data of the thermophilic archaeon Pyrococcus horikoshii, an open reading frame was found which encodes a protein (332 amino acids) homologous with an endoglucanase from Clostridium thermocellum (42% identity), deblocking aminopeptidase from Pyrococcus furiosus (42% identity) and an aminopeptidase from Aeromonas proteolytica (18% identity). This gene was cloned and expressed in Escherichia coli, and the characteristics of the expressed protein were examined. Although endoglucanase activity was not detected, this protein was found to have aminopeptidase activity to cleave the N‐terminal amino acid from a variety of substrates including both N‐blocked and non‐blocked peptides. The enzyme was stable at 90°C, with the optimum temperature over 90°C. The metal ion bound to this enzyme was calcium, but it was not essential for the aminopeptidase activity. Instead, this enzyme required the cobalt ion for activity. This enzyme is expected to be useful for the removal of N α‐acylated residues in short peptide sequence analysis at high temperatures.

Large-scale immobilization of lipase fromPseudomonas fluorescens biotype I and an application for sardine oil hydrolysis

Large-scale production of thermostable lipase fromPseudomonas fluorescens biotype I was carried out in a fermenter with an antifoaming agent and physical deforming treatments. After cultivation, heat treatment was applied to kill the bacteria and to inactivate other enzmes. Large-scale immobilization of the lipase to a macroporous weak-anion exchange resin was performed with a lipase solution that had an ionic strength of less than 0.1 and an ethanol concentration of 50%. Almost all eicosapentaenoic acid and docosahexaenoic acid were liberated continuously from sardine oil by the immobilized lipase in a countercurrent fluidized-bed reactor. The cost of enzyme used in the reactor has been compared with a process in which soluble lipase fromCandida rugosa was used.

Continual conversion of free fatty acid in rice bran oil to triacylglycerol by immobilized lipase

Rice bran oil containing 30–50% free fatty acid was continually converted to an oil containing more than 75% of triacylglycerol (TG) by means of immobilized lipase. The reaction was carried out at 60°C for 24 h with dehydration and reactant mixing by dry nitrogen flow under a positive nitrogen atmosphere. Enzymatic TG synthesis with evaporation by heating was not suitable because of the increasing peroxide value of the oil.

Heat effect on the structure and activity of the recombinant glutamate dehydrogenase from a hyperthermophilic archaeon Pyrococcus horikoshii

Glutamate dehydrogenase from Pyrococcus horikoshii (Pho-GDH) was cloned and overexpressed in Escherichia coli. The cloned enzyme with His-tag was purified to homogeneity by affinity chromatography and shown to be a hexamer enzyme of 290+/-8 kDa (subunit mass 48 kDa). Its optimal pH and temperature were 7.6 and 90 degrees C, respectively. The purified enzyme has outstanding thermostability (the half-life for thermal inactivation at 100 degrees C was 4 h). The enzyme shows strict specificity for 2-oxoglutarate and L-glutamate and requires NAD(P)H and NADP as cofactors but it does not reveal activity on NAD as cofactor. K(m) values of the recombinant enzyme are comparable for both substrates: 0.2 mM for L-glutamate and 0.53 mM for 2-oxoglutarate. The enzyme was activated by heating at 80 degrees C for 1 h, which was accompanied by the formation of its active conformation. Circular dichroism and fluorescence spectra show that the active conformation is heat-inducible and time-dependent.

Continuous lipolysis reactor with a loop connecting an immobilized lipase column and an oil-water separator

A continuous lipolysis system is described that consists of a loop connecting a fixed-bed reactor with the immobilized lipase fromPseudomonas fluorescens biotype I and an oil-water separator. In addition to continuous lipolysis, good continuous separation of oil product and water-soluble product and continuous concentration of glycerol can be integrated in this simple reactor.

Esterification of polyunsaturated fatty acids by various forms of immobilized lipase from Rhizomucor miehei

Ethyl esterification specificity of a lipase from Rhizomucor miehei for polyunsaturated fatty acids (PUFA) was compared at 1 and 100 mM to study molecular recognition of PUFA. The chemical shift of methylene adjacent to carboxyl groups in the nuclear magnetic resonance spectrum of docosahexaenoic acid (DHA) in ethanol moved to a lower magnetic field as the concentration of DHA increased, suggesting that the degree of dissociation of DHA decreased. Specificity constants or apparent second-order rate constants (Vmax/Km or catalytic power) for 1 mM esterification by immobilized lipases were higher than the native lipase. Immobilized hydrophobic carrier of low mass transfer resistance for the esterification substrate may improve maximal velocity and affinity for the substrate. Higher specificity constants for 1 mM substrates were observed using immobilized lipases fixed on an anion exchange resin with glutaraldehyde and on a cation exchange carrier with carbodiimide. Activity yields measured with 1 mM PUFA substrate were high. For the substrates at a concentration of 100 mM, higher specific constants with these bifunctional reagents were not observed but higher activity yields were found.

Triacylglycerol Synthesis from Fatty Acid and Glycerol Using Immobilized Lipase

High free fatty acid (FFA) rice bran oil containing 30-50 % FFA was converted to an oil containing about 75-90 % triacylglycerol (TG) using immobilized lipase. Enzymatic refining of the FFA oil was performed continuously for more than one month using a reactor with two circulation loops, each connecting a fixed bed reactor and a dehydrator. The substrate was the stoichiometric amount of the FFA oil and glycerol required for synthesizing TG. The technology could be applied to synthesizing TG at more than 95 % yield from polyunsaturated fatty acids such as docosahexaenoic acid.