Sorbitol production in charged membrane bioreactor with coenzyme regeneration system: I. Selective retainment of NADP(H) in a continuous reaction

The concept of a charged membrane bioreactor (CMBR) has been proposed for continuous reactions of enzymatic reduction dependent upon the nicotinamide coenzyme NADP(H). It was found that a composite membrane with a negative charge, NTR 7410, could retain NADP(H) selectively without any chemical modification. Several permeation experiments have revealed that the retainment of a coenzyme is based on electrostatic repulsion of negative charges between the membrane and the phosphate moiety of NADP(H). The retainment ratio was reduced by the addition of inorganic salt, although it could be restored to 0.8 in the presence of albumin. A reactor equipped with a charged membrane as the coenzyme separator module was constructed and used in the continuous production of sorbitol. NADPH-dependent aldose reductase isolated from Candida tropicalis IAM 12202 was used for the production of sorbitol from glucose. The coenzyme oxidized in this reaction was enzymatically regenerated by conjugation with glucose dehydrogenase, together with the coproduction of gluconic acid from glucose. With a substrate conversion of 85%, 100 g/L sorbitol was produced and equimolar gluconic acid was coproduced for more than 800 h, indicating that the reaction was efficiently coupled to the enzymatic regeneration. The initial high retainment ratio of the membrane was almost maintained throughout the entire reaction. Consequently, the turnover number of the coenzyme reached 106,000.     

Sorbitol production in charged membrane bioreactor with coenzyme regeneration system: II. Theoretical analysis of a continuous reaction with retained and regenerated NADPH

A theoretical model was constructed in order to study charged membrane bioreactors (CMBRs). In this model, it was postulated that a native nicotinamide coenzyme NADP(H) can be partially retained by a charged membrane in continuous operation. A multienzyme system composed of NADPH-dependent aldose reductase (AR) and glucose dehydrogenase (GDH) was used for the production of sorbitol and gluconic acid from glucose and for the conjugated enzymatic regeneration of NADP(H). Both enzymes were studied with respect to their reaction kinetics. AR was determined to obey the Theorell-Chance mechanism. GDH reaction was approximated by the initial velocity equation of the sequential Bi-Bi mechanism since the reverse reaction could be neglected. Significant inhibitions of both enzymes by sorbitol, gluconic acid, and glucose were observed, and the mode of inhibition was estimated to modify the velocity equations. The differential equation system for each component was derived and numerically analyzed according to the model. The theoretical model elucidated several features of the CMBR. (1) When compared at the same productivity, higher retainment was found to bring about a higher coenzyme turnover number, indicating that the feed coenzyme concentration can be reduced. (2) Under constant conversion, a contradictory relationship between turnover number and residence time arises if the feed concentration of a coenzyme varies. The theoretical model predicts that there is a practically optimal concentration for using NADP(H) efficiently. This concentration was consistent with that yielding the estimated minimum total cost. (3) In this system, excess-GDH-to-AR activity was required because of differences in their kinetic constants. The amount of regeneration enzyme required can be reduced by the accumulation of excels NADPH due to coenzyme retainment. (4) Comparison with an ideal repeated batch reaction revealed that the continuously operated CMBR was vastly superior with respect to productivity as well as operation ability.     

Unfolding and refolding of the constant fragment of the immunoglobulin light chain

The kinetics of reversible unfolding and refolding by guanidine hydrochloride of the constant fragment of the immunoglobulin light chain are described. The kinetic measurements were made at pH 7.5 and 25 °C using tryptophyl fluorescence and farultraviolet circular dichroism.The kinetics of unfolding of the constant fragment showed two phases in the conformational transition zone and a single phase above the transition zone. A double-jump experiment confirmed the presence of two forms of the unfolded molecule. These results were thoroughly explained on the basis of the three-species mechanism, U₁

U₂

N, where U₁ and U₂ are the slow-folding and fast-folding species, respectively, of unfolded protein and N is native protein. The equilibrium constant for the process of U₂ to U₁ was estimated to be about 10 and was independent of the conditions of denaturation. These findings were consistent with the view that the U₁

U₂ reaction is proline isomerization. The rates of interconversion between N and U₂ changed greatly with the concentration of guanidine hydrochloride. On the other hand, the refolding kinetics below the transition zone showed behavior unexpected from the three-species mechanism. Whereas the apparent rate constant of the slow phase of refolding was independent of the refolding conditions, its amplitude decreased markedly with the decrease in the final concentration of guanidine hydrochloride. On the basis of this and other results, formation of an intermediate during refolding was ascertained and the refolding kinetics were consistently explained in terms of a more general mechanism involving a kinetic intermediate probably containing non-native proline isomers. The intermediate seemed to have a folded conformation similar to native protein. Comparison of the refolding kinetics of the constant fragment with those of other domains of the immunoglobulin molecule suggested that Pro143 is responsible for the appearance of the slow phase.     

The binding of ATP to the catalytic and the regulatory site of Ca2+,Mg2+-dependent ATPase of the sarcoplasmic reticulum

Two kinds of ATP binding sites were found on the ATPase molecule in deoxycholic acid-treated sarcoplasmic reticulum. One was the catalytic site (1 mol/mol active site) and its affinity was high. Upon addition of Ca²⁺, all the ATP bound to the catalytic site disappeared at 75 mM KCl, while a significant amount of ATP remained bound to the site at 0–2 mM KCl. The latter binding was found to be due to the formation of a slowly exchanging enzyme-ATP complex, which is in equilibrium with phosphoenzyme + ADP. The other binding site was the regulatory one (1 mol/mol active site) and its affinity was low, changing only insignificantly upon addition of Ca²⁺. The ATP binding to the regulatory site shifted the equilibrium between the slowly exchanging complex and EP toward EP.     

Application of the two-dimensional nmr techniques on a des(Ala,Gly)-somatostatin analog

Two-dimensional nmr techniques have been carried out for the peak assignment of the spectrum of a somatostatin analog. Two-dimensional J-resolved spectroscopy simplified the rather broad and complicated spectrum to show the center of chemical shifts of each resonance and gave information on the coupling profiles. Another technique, two-dimensional spin-echo correlated spectroscopy, revealed the connectivities between protons which are correlated by weak spin–spin couplings. The combination of the results of these two complementary techniques made it possible for us to assign almost all peaks of the spectrum of the 11-residue somatostatin analog.     

Metabolites of mating pheromone,rhodotorucine A, by a cells of Rhodosporidiumtoruloides

Rhodotorucine $\text{A}$ which induces mating tube formation of $\text{a}$ cells in $\text{Rhodosporidium}\text{toruloides}$ is metabolized rapidly by $\text{a}$ cells. By use of labeled rhodotorucine $\text{A}$, the degradation was found to be proteolytic. Two peptide fragments Tyr-Pro-Glu-Ile-Ser-Trp-Thr-Arg and Asn-Gly-Cys(S-farnesyl) were identified as the metabolites. Proteolysis of the pheromone mainly occurred on the cell surface. Culture filtrate of $\text{a}$ cells at log phase did not metabolize rhodotorucine $\text{A}$.     

Modification of human hemoglobin with polyethylene glycol: A new candidate for blood substitute

Human hemoglobin was modified with polyethylene glycols. The conjugates exhibited P₅₀ values of 10–15 mmHg, those are enough to deliver oxygen from the lungs to tissues. The most remarkable characteristic is their long half disappearance time from the circulation. The longest half disappearance time of these derivatives is about 180 minutes in contrast to 45 minutes of free hemoglobin. The half disappearance time shows a good corelation not to molecular weight but to the effective molecular size, which is determined by the elution time of HPLC on a gel permeation column.     

Fibrin membrane endowed with biological function VI. Immobilization of multienzymes of urea cycle

Four enzymes in urea cycle and inorganic pyrophosphatase were immobilized simultaneously into a matrix of fibrin fiber formed from fibrinogen by the concerted action of thrombin and blood coagulation Factor XIII. The immobilized multienzyme system not only had an ability to carry out urea cycle continuously at least over several hours, but also had a greatly improved efficiency over the corresponding soluble system.     

The insecticidal activity of some norditerpene dilactones

The effects on housefly (Musca domestica) of six norditerpene lactones (nagilactones B, D, E, podolide, hallactone B and 14-epi-ponalactone A) in a defined diet were tested. Nagilactone D was the most active, with an LD₅₀ of 0.7 ppm. Nagilactones C and D were also toxic to light-brown apple moth (Epiphyas postvittana) and codling moth (Laspeyresia pomonella).The relationship between lactone structure and toxicity to housefly is discussed.

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Zusammenfassung Viele aus Podocarpus-Arten isolierte Norditerpenlactone sind für Stubenfliegen toxisch. Es wird über die Resultate der Fütterung von sechs Lactonen an die Stubenfliege in einem definierten Nährboden berichtet und die LD₅₀ von zwölf Verbindungen werden verglichen. Der aktivste Stoff ist Nagilacton mit einer LD₅₀ von 0,7 ppm. Nagilacton C und D sind auch toxisch für Epiphyas postvittana und für den Apfelwickler. Die wirksamsten Verbindungen haben eine kurze nichtpolare Seitenkette und eine elektronenreiche, funktionelle Gruppe bei C-8, ferner sind sie Epoxyalkohole in Ring-A. Diese in der Natur vorkommenden Lactone spielen wahrscheinlich eine Schutzrolle in der Pflanze.