Purification and properties ofl-serine dehydratase fromLactobacillus fermentum ATCC 14931

l-Serine dehydratase fromLactobacillus fermentum was purified 100-fold. It was stabilized by the presence of 1 mM l-cysteine in 50 mM phosphate buffer. M_r=150,000 was determined by gel filtration. The enzyme consists of four apparently identical subunits (M_r=40,000) that were observed after treatment with sodium dodecyl sulfate. The apparent K_m forl-serine was 65 mM. Fe⁺⁺ was required for the enzymatic activity, and the apparent K_m value for this reaction was 0.55 mM. Maximum enzymatic activity was observed at 45°C and pH 8.0 in 50 mM phosphate buffer. At pH values different from the optimum, a positive cooperativity between substrate molecules was observed. The activation energy of the reaction was 11,400 and 22,800 cal × mol^–1 for temperature values more than and less than 35°C respectively. The purified enzyme showed a maximum absorption between 400 and 420 nm, indicating the presence of pyridoxal-5-phosphate (PLP) as a prosthetic group. The PLP concentration was 0.027 µmoles per milligram of protein. The data suggest that there is 1 mol of PLP for each protein subunit.     

Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli

Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli.     

Narrow- and Broad-Host-Range Symbiotic Plasmids of Rhizobium spp. Strains That Nodulate Phaseolus vulgaris

Agrobacterium transconjugants containing symbiotic plasmids from different Rhizobium spp. strains that nodulate Phaseolus vulgaris were obtained. All transconjugants conserved the parental nodulation host range. Symbiotic (Sym) plasmids of Rhizobium strains isolated originally from P. vulgaris nodules, which had a broad nodulation host range, and single-copy nitrogenase genes conferred a Fix⁺ phenotype to the Agrobacterium transconjugants. A Fix⁻ phenotype was obtained with Sym plasmids of strains isolated from P. vulgaris nodules that had a narrow host range and reiterated nif genes, as well as with Sym plasmids of strains isolated from other legumes that presented single nif genes and a broad nodulation host range. This indicates that different types of Sym plasmids can confer the ability to establish an effective symbiosis with P. vulgaris.     

Influence of ion gradients on the transbilayer distribution of dibucaine in large unilamellar vesicles

The uptake of dibucaine into large unilamellar vesicles in response to proton gradients (delta pH; inside acidic) or membrane potentials (delta psi; inside negative) has been investigated. Dibucaine uptake in response to delta pH proceeds rapidly in a manner consistent with permeation of the neutral (deprotonated) form of the drug, reaching a Henderson-Hasselbach equilibrium where [dibucaine]in/[dibucaine]out = [H+]in/[H+]out and where the absolute amount of drug accumulated is sensitive to the buffering capacity of the interior environment. Under appropriate conditions, high absolute interior concentrations of the drug can be achieved (approximately 120 mM) in combination with high trapping efficiencies (in excess of 90%). Dibucaine uptake in response to delta psi proceeds more than an order of magnitude more slowly and cannot be directly attributed to uptake in response to the delta pH induced by delta psi. This induced delta pH is too small (less than or equal to 1.5 pH units) to account for the transmembrane dibucaine concentration gradients achieved and does not come to electrochemical equilibrium with delta psi. Results supporting the possibility that the charged (protonated) form of dibucaine can be accumulated in response to delta psi were obtained by employing a permanently positively charged dibucaine analogue (N-methyldibucaine). Further, the results suggest that delta psi-dependent uptake may depend on formation of a precipitate of the drug in the vesicle interior. The uptake of dibucaine into vesicles in response to ion gradients is of direct utility in drug delivery and controlled release applications and is related to processes of drug sequestration by cells and organelles in vivo.     

Predictors of success in hypertensives treated with biofeedback-assisted relaxation

This paper describes differences in response in seventeen patients with essential hypertension who participated in a treatment program consisting of electromyograph biofeedback assisted relaxation training. Responders were found to have higher treatment values of urinary and plasma cortisol, Trait Anxiety and forehead muscle tension compared to treatment failures. Responders also sustained greater decreases in plasma, and urinary cortisol after treatment. These data are discussed in light of the ability to predict which hypertensive patients may be most benefitted by a relaxation based treatment.We would like to thank Dr. Charles Spielberger for his permission to use the State-Trait Anxiety Inventory. We thank Michael Robinson for assistance with statistical analysis.     

Effect of Drying Medium on Residual Moisture Content and Viability of Freeze-Dried Lactic Acid Bacteria

The effect of various substances on the relationship between residual moisture content and the viability of freeze-dried lactic acid bacteria has been studied. Compounds such as polymers, which display considerable ability in displacing water, showed no protective action during freeze-drying. Adonitol, on the other hand, produced the smallest change in water content at various times during drying and allowed the highest rate of survival.     

The antenna system of Rhodospirillum rubrum. Detection of macromolecular constituents not stainable by Coomassie brilliant blue in solubilized preparations of the B880 complex

A solubilized preparation of the major Rhodospirillum rubrum antenna complex (B880) was obtained by a described procedure and its polypeptide composition was analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Only two polypeptides of molecular weights close to 7000 were detected after staining the gels with Coomassie brilliant blue. However, several other constituents could be visualized by silver staining or by an immunochemical method. When the preparation was chromatographed on Sephacryl, some of the resulting fractions exhibited the characteristic B880 absorption spectrum and contained only the two proteins that were detectable with Coomassie brilliant blue. In those fractions the A ₂₈₀/A ₈₈₀ratio was 0.4, which indicated a significant improvement of the bacteriochlorophyll to protein ratio over the unchromatographed preparation (A ₂₈₀/A ₈₈₀=0.7). Other chromatography fractions lacked bacteriochlorophyll and contained a carotenoid which seemed to be bound to protein. The macromolecular constituents present in these latter fractions differed from those associated to the purified B880 complex in their electrophoretic moblities and/or in their staining properties. That suggested the possible existence of a carotenoprotein that did not result from the B880 complex upon loss of bacteriochlorophyll.     

Effect of ozone on ribosomes in pinto bean leaves

A study was made of cytoplasmic and chloroplast ribosomes in the primary leaves of pinto bean plants exposed to ozone. The isolated ribosomes were analysed by sucrose density gradient. Ozone at the levels of 0·35 ppm for 20–35 min does not change the concentrations of various sedimenting particles of the cytoplasmic ribosomes. Ozone at similar levels, however, specifically decreases the population of chloroplast ribosomes per unit fresh weight of leaves. The distribution pattern of these chloroplast ribosomes is characterized by the low concentration of the fast-sedimenting polysome particles concomitant with the low magnitude of other slow-sedimenting components. The kinetics of ribosome populations during leaf growth demonstrates that ozone does not influence the daily levels of different ribosomal components of cytoplasmic ribosomes. However, ozone prematurely decreases the concentrations of polysomes and other components of chloroplast ribosomes below control level at the early stage of leaf development. These findings are discussed to explain initiation of the premature senescence caused by ozone.