Photoreaction of bacteriorhodopsin at high pH: origins of the slow decay component of M.

The absorption spectrum of light-adapted purple membrane in 3 M KCl is dependent on temperature even in the room temperature region. Temperature-induced difference spectra at various pH values suggested that the trans isomer of bacteriorhodopsin, bR570, is in thermal and/or photodynamic equilibrium with several different conformers. The major second conformer occurring at neutral pH had the same spectroscopic properties as the 13-cis isomer, and its content at 35 degrees C was estimated to be more than 20%. Heterogeneity in the protein conformation became more significant above pH8, where temperature-induced difference spectra exhibited a negative peak at 580 nm and a positive peak at 296 nm. This absorption change is very similar to that observed upon the formation of the N intermediate, suggesting that an N-like conformer occurs at high pH and temperature. A significant temperature dependence was also seen in the M decay kinetics at high pH, which were described by two decay components; i.e., the fast decaying M (Mf) was predominant at low temperature, but the amplitude of the slow component (M(s)) increased with increasing temperature. It is suggested that M(s) is generated upon excitation of the N-like conformer, in which the residue (Asp-96) usually acting as a proton donor to the Schiff base is deprotonated. The N-like conformer could be N itself, because M(s) was enhanced when N was accumulated by background light. A strong correlation between the amplitude of M(s) and the concentration of N was also revealed by the accumulation kinetics of Mf, M(s), and N after the onset of continuous actinic light.(ABSTRACT TRUNCATED AT 250 WORDS)     

Early changes in mitochondrial monoamine oxidase activity of rat liver during 2-acetylaminofluorene feeding

The activities of mitochondrial type A and B monoamine oxidase were determined in the liver of rats fed a diet containing 2-acetylaminofluorene (AAF). Three days after the initiation of AAF-feeding, there was a significant decrease of type B monoamine oxidase activity without affect on type A enzyme. The decreased activity of type B monoamine oxidase, which reached a minimum after three weeks, was sustained for as long as AAF-feeding was continued. Sex-related difference in response to AAF was seen in the rat with respect to the onset and the intensity of the decreased type B monoamine oxidase activity, male rats being more sensitive to the carcinogen than female rats. In contrast to the in vivo effect, AAF showed a potent inhibitory effect on type A monoamine oxidase, rather than on type B enzyme, when added in vitro. The pI₅₀ values were estimated to be 7.5 against type A monoamine oxidase and 4.1 against type B enzyme, respectively. The in vitro inhibition of both types of monoamine oxidase by AAF was competitive. The K_i values for AAF were calculated to be 9.51 · 10^?9 M for type A monoamine oxidase and 1.30 · 10^?5 M for type B enzyme, respectively. In accordance with the potent inhibitory effect of AAF on type A monoamine oxidase in vitro, a single administration of the carcinogen, at a dose of 50 mg/kg, resulted in a marked and temporal decrease of the enzyme activity in the mitochondria of male rat liver. Recovery of the decreased type B monoamine oxidase activity was slow, and the enzyme activity did not return to control levels, even if rats were fed the basal diet for 2 or 4 weeks after the cessation of AAF-feeding.     

Sequential polymerization of flagellin A and flagellin B into Caulobacter flagella

The mode of polymerization of two species of flagellins, flagellin A and flagellin B, in polar flagella of Caulobacter crescentus was examined. By immunological staining we found that 1 to 1.2 μm of the portion of the flagellar filament proximal to the cell was composed of flagellin B, whereas about 5 μm of the distal portion was composed of flagellin A. This result, together with the previous observation that a flagellin B-less mutant cannot form normal flagella but instead forms stubs in spite of their high level of flagellin A synthesis, indicates that flagellin B is very important for the formation of complete flagella and/or for the initiation of filament formation from the hook.     

Morphological and anatomical studies inTribulus terrestris

Seedling morphology and vascular course inTribulus terrestris were studied. This species has no erect stem, but four buds appear immediately above the cotyledonary node and grow into prostrate shoots. They were determined to be the main axis of the seedling and the axillary branches of the earliest three foliage leaves, which arise very close to each other. All the leaves, including cotyledons, are vascularized with four bundles among which two are related to a single median gap. When two leaves are attached to one node, lateral traces to the opposed leaves are derived by bifurcation of a single bundle at either side of the stem. In the shoot with a series of alternate leaves, the median pair of traces to every other leaf are found on the same orthostichy. In the branch of which the first node bears no flower but an anisophyllous pair of leaves, the smaller leaf at the node was proven to be the first prophyll because its median traces are superposed by those to the leaf at the next node.     

The Separation and Characterization of Carbohydrate Rich Component from Ovomucin in Chicken Eggs

We investigated the effects of near-infrared irradiation on the photoconversion of Chenopodium album water-soluble chlorophyll-binding protein (CaWSCP) in the presence of sodium hydrosulfite and found a further photoconversion from CP742 to CP763, a novel form of CaWSCP. Interestingly, one-third of the absorption peak at 668 nm was recovered in CP763, but re-irradiation under oxidative conditions eliminated the photo convertibility of CaWSCP.     

Automated high-performance liquid chromatographic method for determination of furosemide in dog plasma

An automated high-performance liquid chromatographic method for the determination of the diuretic drug furosemide has been established. Dog plasma was injected directly into a two-column system with a BSA—ODS (ODS column coated with bovine serum albumin) precolumn and a C₁₈ analytical column for the separation of furosemide. The two columns were automatically switched. Furosemide remained trapped on the precolumn while proteins were eluted to waste. After column switching, furosemide was washed onto the analytical column and analysed without interference. The greatest advantage of the method is its easy performance without manual sample preparation; it requires no extraction or deproteinization. The method allows determination of 0.1–10 μg/ml of furosemide with accuracy and precision comparable with previously reported values. The coefficients of variation obtained from replicate measurements of 1 μg/ml and 5 μg/ml samples were 1.65% and 2.40%, respectively. This method was used to measure the plasma levels of furosemide in beagle dogs to whom the drugs was administered, as a reference, in a toxicological study.