Hydrogen evolution by co-immobilized Chlorella vulgaris and Clostridium butyricum cells

Whole cells of Chlorella vulgaris and Clostridium butyricum were co-immobilized in 2% agar gel. NADP was suitable as an electron carrier. The rate of hydrogen evolution increased with increasing NADP concentration. The optimum conditions for hydrogen evolution were pH 7.0 and 37°C. The immobilized C. vulgaris-NADP-immobilized Cl. butyricum system continuously evolved hydrogen at a rate of 0.29–1.34 μmol/h per mg Chl for 6 days. On the other hand, the system without NADP evolved only a trace amount of hydrogen.     

Quantitative measurement of caspase-3 activity in a living starfish egg

If not fertilized, synchronous apoptosis is induced in starfish eggs at approximately 11h after stimulation with the hormone, 1-methyladenine. In this study, a membrane-impermeant substrate of caspase-3, acetyl-Asp-Glu-Val-Asp-coumarylamido-4-methanesulfonic acid (Ac-DEVD-CAMS), was synthesized and microinjected into a starfish egg. Caspase-3 activity in unfertilized egg was detected approximately 30min before blebbing by quantifying the accumulation rate of a membrane-impermeant, fluorogenic product, 7-aminocoumarin-4-methanesulfonic acid (ACMS), using a photomultiplier mounted on a fluorescence microscope. When active recombinant human caspase-3 was microinjected into an egg at 3h after 1-methyladenine treatment, the injected caspase-3 activity decreased and disappeared within 2h. This decrease is probably due to proteasome-dependent degradation of the enzyme, since the injected caspase-3 was degraded and a proteasome inhibitor blocked its degradation. In contrast, in aged eggs at approximately 10h after 1-methyladenine treatment, no degradation of the injected caspase-3 was observed, suggesting that endogenous caspase-3 may stabilize at this point, therefore, inducing apoptosis.     

Radical-Mediated Cyclization of A 6-Chloro-9-(2-Deoxy--d erythro-pent-1-enofuranosyl)-8-(2,2-dibromovinyl) purine

Abstract

A vinyl radical generated from a 6-chloro-9-(2-deoxy--d eryrhro-pent-l-enofuranosyl)-8-(2,2-dibromovinyl) purine effected cyclization either at the 1′-or at the 2′-position. The result is discussed in comparison with our previous study of the corresponding uracil derivative.     

A deterministic mechanism producing the loose coupling phenomenon observed in an actomyosin system

Myosins are molecular motors that convert the chemical energy of ATP into mechanical work called a power stroke. Class II myosin engaged in muscle contraction is reported to show a "loose coupling phenomenon", in which the number of power strokes is greater than the number of ATP hydrolyses. This phenomenon cannot be explained by the lever-arm hypothesis, which is currently accepted as a standard theory for myosin motility. In this paper, a model is proposed to reproduce the loose coupling phenomenon. The model is based on a mechanochemical process called "Driven by Detachment (DbD)" mechanism, which assumes that the energy of the power strokes originates from the potential energy generated by the attractive force between myosin and actin. During the docking process, the potential energy is converted into an intramolecular strain in a myosin molecule, which drives the power stroke after the myosin is firmly attached to an actin filament. The energy of ATP is used to temporarily reduce the attractive force and to increase the potential energy. Therefore, it is not directly linked to the power strokes. When myosin molecules work as an aggregate, the sliding movement of a myosin filament driven by the power strokes of some myosin heads makes other myosin heads that have completed their power strokes detach from the actin without consuming ATP. Under the DbD mechanism, these passively detached myosins can be again engaged in power strokes after the next attachment to actin. As a result, the number of power strokes becomes greater than the number of ATP hydrolyses, and the loose coupling phenomenon will be observed. A theoretical analysis indicates that the efficiency of converting the potential energy into intramolecular elastic energy determines the number of power strokes per each ATP hydrolysis. Computer simulations showed that the DbD mechanism actually produced the loose coupling phenomenon. A critical requirement for this mechanism is that ATP must preferentially facilitate the detachment of myosins that have completed their power strokes, but are still strongly attached to the actin. This requirement may be fulfilled by ATP hydrolysis tightly depending on the conformation of a myosin molecule.     

Thermostable tryptophan synthase ofBacillus stearothermophilus expressed inEscherichia coli

Summary The tryptophan synthase genes,trpA andtrpB, from a moderate thermophile,Bacillus stearothermophilus IFO13737, were expressed efficiently inEscherichia coli. The recombinant tryptophan synthase amounted to 22% of the soluble cellular protein, and was purified to homogeneity by three steps. The enzyme is more thermostable thanE.coli tryptophan synthase, especially the subunit. The enzyme is also more resistant to sodium dodecylsulfate and methanol thanE.coli enzyme.     

Triterpenoid saponins from Fatsia japonica

Five triterpenoid saponins isolated from the flowers, the mature fruits and the leaves of Fatsia japonica were identified as 3-O-[β-d-glucopyranosyl(1→4)-β-d-glucopyranosyl]-hederagenin (1), 3-O-[β-d-glucopyranosyl-(1→4)-α-l-arabinopyranosyl]-oleanolic acid (2), 3-O-[α-l-arabinopyranosyl]-hederagenin (3), 3-O-[β-d-glucopyranosyl]-hederagenin (4) and 3-O-[β-d-glucopyranosyl(1→4)-α-l-arabinopyranosyl]-hederagenin (5). The saponins 1 and 2 are new, naturally occurring, triterpenoid saponins. The distribution of the five saponins in three parts of the plant was investigated. Saponins 2, 3 and 5 were present in the flowers, saponins 1, 3, 4 and 5 were in the mature fruits and saponins 2, 3, 4 and 5 were in the leaves.     

An NADP-Glutamate Dehydrogenase from the Green Alga Bryopsis maxima. Purification and Properties

NADP-glutamate dehydrogenase (EC 1.4.1.4[EC]; NADP-GDH) was purifiedto electrophoretic homogeneity from the multinuclear-unicellulargreen marine alga in Sipho-nales, Bryopsis maxima, and its propertieswere examined. M_r of the undenatured enzyme was 280 kDa, andthe enzyme is thought to be a hexamer of 46 kDa subunit protein.Optimum pHs for the reductive amination and oxidative deaminationwere 7.5 and 8.2-9.0 respectively. The enzyme displayed NADPH/NADH-specificactivities with a ratio of 18 :1. Apparent K_m values for 2-oxoglutarate,ammonia, NADPH, glutamate and NADP⁺ were 3.0, 2.2, 0.03, 3.2and 0.01 mM respectively. The enzymochemical characteristicsof the GDH were studied and compared to those of other species.The B. maxima GDH was insensitive to 5 mM Ca²⁺ and to 1 mM EDTAin contrast to higher plant NAD-GDHs. Chemical modificationswith DTNB and pCMBS suggested that cysteine residues are essentialfor the enzymatic activity as in other species GDHs. The GDHwas not affected by 1 mM purine nucleotides, suggesting thatthe enzyme is not allosteric, in contrast to animal NAD(P)-GDHsand fungal NAD-GDHs. (Received August 12, 1996; Accepted January 7, 1997)