The effect of tyrosine nitration on the physicochemical properties and reactivity of human respiratory cytochrome c has been extensively analyzed. A set of mutants, each bearing only one tyrosine out of the five present in the wild-type molecule, has been constructed in order to study the effect of each tyrosine nitration on the properties of the whole protein. Replacement of tyrosines by phenylalanines does not promote significant changes in the properties of the cytochrome. Nitration of wild-type cytochrome c promotes a drastic decrease (ca. 350 mV) in the midpoint redox potential, probably induced by nitration of both tyrosines 48 and 67. Nitration also promotes a significant decrease in the intrinsic reactivity of all the wild-type and mutant proteins. Nitration of mutant cytochromes and, in particular, of the wild-type protein significantly decreases their reactivity with cytochrome c oxidase, thereby suggesting that this alteration is due to an accumulative effect of different nitrations. The reactivity of mutants bearing tyrosine 67 and, to a lesser extent, tyrosine 74 is more affected by nitration, indicating that the change in reactivity of nitrated wild-type cytochrome c is mainly due to nitration of these tyrosine residues. Moreover, nitration of wild-type cytochrome c induces a significant loss in its ability to activate caspases because of the additive effect of nitration of several tyrosine groups, as inferred from the behavior of monotyrosine mutants.

The fragmentation dynamics of aggregate of non-Brownian particles in shear flow is investigated numerically. The breakup behaviors of aggregates having the same connectivity but the different space-filling properties are examined. The Lagrangian particle simulation in a linear flow field is performed. The effect of surrounding fluid on the motion of multiple particles is estimated by Stokesian dynamics approach. The inter-particle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The results obtained in this work indicate that the fragmentation behavior of colloidal aggregates depends on their fractal structure. However, if the resultant aggregate size is smaller than the critical one, the fragmentation behavior shows the universality regardless of their original structure. Furthermore, the restructuring of aggregate in shear flow and its effect on the fragmentation process are also discussed

Organotin compounds such as triphenyltin (TPT) and tributyltin (TBT) act as endocrine disruptors through the peroxisome proliferator–activated receptor γ (PPARγ) signaling pathway. We recently found that TPT is a particularly strong agonist of PPARγ. To elucidate the mechanism underlying organotin-dependent PPARγ activation, we here analyzed the interactions of PPARγ ligand-binding domain (LBD) with TPT and TBT by using X-ray crystallography and mass spectroscopy in conjunction with cell-based activity assays. Crystal structures of PPARγ-LBD/TBT and PPARγ-LBD/TPT complexes were determined at 1.95 Å and 1.89 Å, respectively. Specific binding of organotins is achieved through non-covalent ionic interactions between the sulfur atom of Cys285 and the tin atom. Comparisons of the determined structures suggest that the strong activity of TPT arises through interactions with helix 12 of LBD primarily via π-π interactions. Our findings elucidate the structural basis of PPARγ activation by TPT.

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Morinda citrifolia L. (Rubiaceae), known as "noni," is a small tree that grows widely across Polynesia. In Japan, it is called "Yaeyama-aoki" and grows in Okinawa Prefecture. In Polynesia, M. citrifolia has traditionally been used for antibacterial, antiviral, antifungal, antitumor, antihelmin, analgesic, hypotensive, anti-inflammatory, and immune enhancing effects.1) Furthermore, "noni juice," which is made from the fruit of this plant, is today widely drunk for its purported ability to prevent lifestyle-related diseases such as diabetes, hypertension, and cardiopathy and cerebral apoplexy caused by arteriosclerosis. In our previous study, six lignanes which inhibit the LDL oxidation process leading to arteriosclerosis were isolated from the fruit of M. citrifolia.2) Other pharmacological studies of M. citrifolia reported that iridoids isolated from the leaves of this plant inhibited UVB-induced Activator Protein-1 activity 3) and the fruit of this plant prolonged the life span of C57BL/6 mice infected with Lewis lung carcinoma.4) The above reports suggest that M. citrifolia leaves and fruits exhibit some anticancer effects. In addition, M. citrifolia root exhibited an analgesic effect. 5)During the course of our search for natural products capable of preventing lifestyle-related diseases, we have investigated the ability of the chemical constituents of M. citrifolia roots to improve hyperglycemia or diabetes. In this study, we used streptozotocin (STZ)-induced diabetic mice, which is known as an insulin-deficiency model, to demonstrate the effects of M. citrifolia roots on blood glucose levels. MATERIALS AND METHODS Plant MaterialThe roots of M. citrifolia were collected at Okinawa in August 2004. A voucher specimen has been retained in our laboratory.Animals Male ddY mice weighing ca. 30 g (5 weeks old) were obtained from SLC (Osaka, Japan). The animals were housed at a temperature of 23-24°C with a 12 h light-dark cycle (lights on 8:00 a.m. to 8:00 p.m.). Food and water were available ad libitum. The present study was conducted in accordance with the Guiding Principles for the Care and Use of Laboratory Animals, adopted by the Japanese Pharmacological Society.Streptozotocin (STZ)-Induced Diabetic Model Mice were injected intraperitoneally (i.p.) with 200 mg/kg STZ (Sigma-Aldrich, St. Louis, MO, U.S.A.) prepared in 0.1 N citrate buffer adjusted to pH 4.3. Only mice with plasma glucose levels greater than 400 mg/dl were considered as diabetic.Measurement of Blood Glucose Levels The plasma glucose levels in the mice were measured using the Glucose Pilot (Aventir Biotech, CA, U.S.A.) in blood samples obtained from tail vein at 0 or 5 h after a single administration of MeOH extract and CHCl 3 , EtOAc, n-BuOH and H 2 O soluble phases of M. citrifolia roots (each at 3 g/kg, oral route, p.o.).General Procedures Optical rotations were measured using a Jasco DIP-1000 digital polarimeter. IR and UV spectra were measured on a Shimadzu FT-IR 8300 infrared spectrometer and a Hitachi U-3000 spectrometer, respectively. NMR ...

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Abstract. The gravitational settling of inhomogeneously suspended particles in fluid has been investigated. Of particular interest is whether collective or individual motion of particles is dominant during their settlings, i.e., whether the particles settle as a continuous suspension or they settle individually relative to surrounding fluid. We observed the settling of a stratified suspension which has the lower and upper concentration interfaces in quasi-two dimensional vessel. In some cases, the suspension behaves perfectly as a continuous fluid and the motion of the constituent particle is subject to bulk flow caused by the interfacial instability. In other cases, the particle behaves individually relative to surrounding fluid. The existence of concentration interface plays a significant role in these extreme behaviors of suspension. The transition from the collective to individual behaviors can be predicted quantitatively by a parameter which expresses the border resolution of concentration interface.

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