Low- and high-affinity transport systems for citric acid in the yeast Candida utilis.

Citric acid-grown cells of the yeast Candida utilis induced two transport systems for citric acid, presumably a proton symport and a facilitated diffusion system for the charged and the undissociated forms of the acid, respectively. Both systems could be observed simultaneously when the transport was measured at 25 degrees C with labelled citric acid at pH 3.5 with the following kinetic parameters: for the low-affinity system, Vmax, 1.14 nmol of undissociated citric acid s-1 mg (dry weight) of cells-1, and Km, 0.59 mM undissociated acid; for the high-affinity system, Vmax, 0.38 nmol of citrate s-1 mg (dry weight) of cells-1, and Km, 0.056 mM citrate. At high pH values (above 5.0), the low-affinity system was absent or not measurable. The two transport systems exhibited different substrate specificities. Isocitric acid was a competitive inhibitor of citric acid for the high-affinity system, suggesting that these tricarboxylic acids used the same transport system, while aconitic, tricarballylic, trimesic, and hemimellitic acids were not competitive inhibitors. With respect to the low-affinity system, isocitric acid, L-lactic acid, and L-malic acid were competitive inhibitors, suggesting that all of these mono-, di-, and tricarboxylic acids used the same low-affinity transport system. The two transport systems were repressed by glucose, and as a consequence diauxic growth was observed. Both systems were inducible, and not only citric acid but also lactic acid and malic acid may induce those transport systems. The induction of both systems was not dependent on the relative concentration of the anionic form(s) and of undissociated citric acid in the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the mechanism of bacteriorhodopsin solubilization by surfactants

Purple membrane bacteriorhodopsin can be easily solubilized by Triton X-100 and other detergents, but not by deoxycholate. In order to understand this behavior, we have examined the effects of a variety of surfactants. We show that detergents containing the cholane ring (cholate, taurocholate, 3[(3-cholamidopropyl)diethyl-ammonio]propanesulfonic acid...) are virtually unable to solubilize native bacteriorhodopsin. However, when the protein is reconstituted in dimyristoyl phosphatidylcholine and solubilization is assayed at a temperature such that bacteriorhodopsin is in the form of monomers, solubilization by cholane detergents does occur. We propose that steric factors prevent access of the rigid planar surfactant molecules to the hydrophobic protein regions. These are perhaps located in the monomer-monomer interface, whose solvation by surfactants is essential for solubilization to occur. We note that the capacity of some detergents to solubilize bacteriorhodopsin is always associated within the same range of surfactant concentrations with bleaching (partial or total) of the protein chromophore. The detergent-induced bleaching is at least partially reversible, suggesting that free retinal remains associated to some membrane components. While some surfactant molecules remain tightly bound to the membrane protein, cholane detergents can be completely removed from bacteriorhodopsin. Our results indicate that a structure-function relationship exists for detergents applied to the solubilization of bacteriorhodopsin.     

Nitrification and denitrification in a system of reciprocating jet bioreactor

Concept of separation of stages coupled with novel design of reciprocating jet bioreactor have been incorporated in this research for the development of high efficiency treatment system for contaminated wastewaters.Evaluation of pilot plant data reveals that a three stage reciprocating jet bioreactor system could be effectively employed for nitrification and denitrification of highly polluted wastewater obtained from Berlin wastewater treatment plant. Such a system with COD destruction stage (residence time 1–3 hours) followed by nitrification stage (residence time 3–4.5 hours) and denitrification stage (residence time 0.3 hours) gives COD destruction rate upto 58 kg COD/(m³ day), nitrification rate upto 3.2 NH ₄ ⁺ -N/(m³ day) and denitrification rate upto 28 kg NO ₃ ^– -N/(m³ day) while providing COD, NH ₄ ⁺ -N and NO ₃ ^– -N conversion of more than 90%.Nitrification and denitrification of wastewater at such a short residence time is possible mainly due to the employment of reciprocating jet bioreactor system.Paper presented at the Third Joint Schlesinger Seminar on Transport phenomena and processes in biological systems, Technion — Israel Institute of Technology, Haifa, Israel, May 8–9, 1990     

In vivo lipid and amino acid synthesis from 3-hydroxybutyrate in 15-day-old chick.

The in vivo utilization of 3-hydroxybutyrate for lipid and amino acid synthesis in liver, kidney and duodenal mucosa of overnight-starved 15-day-old chicks has been investigated. Lipid synthesis was higher in liver and duodenal mucosa than in kidney. Triglycerides were the main lipids synthesized from 3-hydroxybutyrate in liver and kidney, while in duodenal mucosa a higher amount of phospholipids was observed. This tissue utilized a high percentage of 3-hydroxybutyrate for the synthesis of free cholesterol, in agreement with the major role of intestine in body cholesterogenesis. All of the assayed tissues synthesized amino acids from 3-hydroxybutyrate at a similar rate, glutamate being always the main amino acid formed.     

Characterization of a Manganese Superoxide Dismutase from the Higher Plant Pisum sativum

A manganese-containing superoxide dismutase (EC 1.15.1.1) was fully characterized from leaves of the higher plant Pisum sativum L., var. Lincoln. The amino acid composition determined for the enzyme was compared with that of a wide spectrum of superoxide dismutases and found to have a highest degree of homology with the mitochondrial manganese superoxide dismutases from rat liver and yeast. The enzyme showed an apparent pH optimum of 8.6 and at 25°C had a maximum stability at alkaline pH values. By kinetic competition experiments, the rate constant for the disproportionation of superoxide radicals by pea leaf manganese superoxide dismutase was found to be 1.61 × 10⁹ molar⁻¹·second⁻¹ at pH 7.8 and 25°C. The enzyme was not sensitive to NaCN or to H₂O₂, but was inhibited by N₃⁻. The sulfhydryl reagent p-hydroxymercuribenzoate at 1 mm concentration produced a nearly complete inhibition of the manganese superoxide dismutase activity. The metal chelators o-phenanthroline, EDTA, and diethyldithiocarbamate all inhibited activity slightly in decreasing order of intensity. A comparative study between this higher plant manganese superoxide dismutase and other dismutases from different origins is presented.     

A brief comparative study of four disposable bubble oxygenators

Four widely used bubble oxygenators-the Optiflo I, the Bentley Q 200 A, the Harvey 200, and the Shiley 100 A-were tested and compared in 182 patients undergoing cardiac valve surgery. Fifty-six cases were performed with normothermia and 126 cases incorporated mild hypothermia (28-30 degrees C). There was no significant difference in the average age of the patients (51 yrs) or the perfusion time (60 min). All components of the extracorporeal circuit were identical, and anesthetic regimens and surgical techniques were also similar. In this study, the Shiley 100 A oxygenator was found to be the most suitable for cases requiring mild hypothermia and was generally considered to be the oxygenator of choice.     

The effect of silicon on the manganese nutrition of soybeans (Glycine max (L.) Merrill)

Summary Silicon during the early vegetative stage did not affect the oven dry weight of any of the various tissues of the soybean plant. Silicon did, however, decrease the Mn concentration in the youngest fully mature leaf at intermediate levels of Mn. This effect did not occur at the lowest or highest Mn levels. Deficiency and toxicity symptoms were moderated to a slight degree by Si except at the highest level of Mn.