Base-exchange reactions of the phospholipids in cardiac membranes

Canine cardiac microsomes were shown to incorporate the nitrogenous bases, serine, ethanolamine, and choline, into their respective phospholipids by the energy-independent, Ca2+-stimulated base-exchange reactions. The optimal Ca2+ concentration was 2.5 mM. Metal ions other than Ca2+ either inhibited or had no effect on the activities. La3+ and Mn2+ were both potent inhibitors. The pH optimum for the reactions at 2.5 mM Ca2+ was approx. 7.8 and depended upon Ca2+ concentration. Apparent Km values at 2.5 mM Ca2+ were 0.06 mM for L-serine, 0.13 mM for ethanolamine and 0.49 mM for choline. The kinetic and metal ion inhibition studies suggest that the choline-exchange reaction is a separate process from the serine and ethanolamine reactions. The ATP-stimulated Ca2+ binding system of the cardiac membranes was not related to the base-exchange reactions; however, the energy-independent Ca2+ binding to the membranes appears to be related to the exchange reactions.     

Participation of quinone and cytochrome b in tetrathionate reductase respiratory chain of Citrobacter freundii.

Formate dehydrogenase, NADH dehydrogenase, a quinone and a b-type cytochrome characterized by maxima at 429 and 560 nm are shown to participate in the tetrathionate redox chain of Citrobacter.     

Base exchange reactions of the phospholipids in rat brain particles

A particulate fraction from rat brain catalyzes the incorporation of [(14)C]choline, [(14)C]ethanolamine, and l-[(14)C]serine into phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, respectively. The reaction appears to be energy-independent since Mg(2+), CTP, ATP, and NaF have no stimulatory action. The incorporation is inhibited by EDTA and activated by Ca(2+). The pH optimum for the incorporation of choline is 9.5, for ethanolamine it is 9.0, and for l-serine it is 8.5. Tris, bicine, and imidazole buffers are inhibitory. The incorporations are inhibited by a variety of structurally related alcohols and are stimulated by isoserine (alpha-hydroxy,beta-aminopropionic acid).     

Participation of acid phospholipids in protein translocation across the bacterial cytoplasmic membrane

Recent observations confirm the participation of acid phospholipids in protein translocation. The hypothesis proposed coupled protein translocation with transmembrane movement of acid phospholipids, their metabolism as a precursor of cell envelope components and recycling. These factors ensure the unidirectional vector value of the secretion, restoration of the membrane site competent for protein translocation and its self-organization.     

Crystallization of porin using short chain phospholipids

A protein from outer membranes of Escherichia coli K-12, porin OmpF was crystallized either with short acyl chain phospolipids or with various detergents as amphiphiles. In dihexanoyl phosphatidylcholine, crystals greater than 0.3 mm in all dimensions were obtained that diffract X-rays beyond 3.5 A. Crystal morphology and unit cell dimensions were indistinguishable from those of detergent-grown crystals, indicating that the role of the phospholipids used is similar to those of many conventional detergents.     

Fatty chain composition of phospholipids in sea urchin spermatozoa

1. An analysis was made of lipids extracted from the spermatozoa of the sea urchins, Hemicentrotus pulcherrimus and Anthocidaris crassispina. 2. Nearly all the lipids from both species consisted of phospholipids (about 80%) and cholesterol (about 14%). Triglyceride and cholesterol ester were present in trace amounts. 3. The fatty acid composition of each phospholipid was determined by gas-liquid chromatography. In both species, the fatty acid consisting of phosphatidylethanolamine was of the unsaturated type for the most part, while cardiolipin was comprised to a considerable degree of saturated fatty acids. In phosphatidylcholine and phosphatidylserine from H. pulcherrimus sperm, unsaturated fatty acid content was somewhat higher than that in phospholipids from A. crassispina sperm.     

The respiratory chain of anaerobically grown Escherichia coli: reactions with nitrite and oxygen

The reactions of nitrite and oxygen with the cytochrome d oxidase of Escherichia coli were studied, following growth of cells on glycerol with fumarate as respiratory oxidant. Optical difference spectroscopy was used to investigate the kinetics of product formation during the reaction of the respiratory chain with nitrite. Two kinetically distinct species were formed in the reaction with nitrite; these had spectral features at 438 nm and 630 nm. These observations indicate that the cytochrome d does not contribute significantly to absorbance in the Soret region, and that changes elicited by ligand binding in the Soret region are largely attributable to haemoprotein b-590. Inhibition of respiratory oxidase activity by nitrite was also investigated. The inhibition was competitive with oxygen (Ki 0.83 mM, pH 7), which allowed analysis of the reaction of the oxidase with oxygen itself. The reaction with oxygen was cooperative with an apparent number of oxygen-binding sites, n, of 1.26 at pH 7, increasing to 1.72 at pH 6. We propose a model for the oxidase in which there are two ligand-binding sites.     

Supersizing the mitochondrial respiratory chain

The complexes of the mitochondrial respiratory chain assemble into higher-order structures called supercomplexes or respirasomes that are thought to be important in channeling electron flow and controlling ROS production. A number of recent papers identify the first protein factors necessary for supercomplex assembly and stability.     

Function of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions of the mitochondrial respiratory chain

Resolution and reconstitution has been used to examine the involvement of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions in this region of the mitochondrial respiratory chain. The iron-sulfur protein is required for electron transfer from succinate and from ubiquinol to cytochrome c1. It is not required for reduction of cytochrome b under these conditions, but it is required for oxidation of cytochrome b by cytochrome c plus cytochrome c oxidase. Removal of the iron-sulfur protein from the b-c1 complex prevents reduction of both cytochromes b and c1 by succinate or ubiquinol if antimycin is added to the depleted complex. As increasing amounts of iron-sulfur protein are reconstituted to the depleted complex, the amounts of cytochromes b and c1 reduced by succinate in the presence of antimycin increase and closely parallel the amounts of ubiquinol-cytochrome c reductase activity restored to the reconstituted complex, measured before addition of antimycin. The function of the iron-sulfur protein in these oxidation-reduction reactions is consistent with a cyclic pathway of electron transfer through the cytochrome b-c1 complex, in which the iron-sulfur protein functions as a ubiquinol-cytochrome c1/ubisemiquinone-cytochrome b oxidoreductase.     

Participation of mesencephalic structures in vocal reactions]

Electrical stimulation and ablation of the midbrain structures in hens and one-day old chickens have revealed the structures (ICO, MLD, MLV, IPC and IMC) involved in the formation of vocal reactions. The paper outlines the functional characteristics of the structures and their dissimilarities which are determined by the type of their units. In the course of individual development of the hens, there is an increase of excitability and lability of the nervous processes in the examined structures.     

On the role of ubiquinone in the respiratory chain

(1) The V₁ (substrate-Q oxidoreductase activity) and V₂ (QH₂ oxidase activity) for the oxidation of substrates by submitochondrial particles have been measured by using heptylhydroxyquinoline N-oxide (HQNO) as inhibitor of V₂. (2) Partial destruction of the Rieske Fe-S cluster by treatment with BAL (2,3-dimercaptopropanol)+O₂ has the same effect on the QH₂ oxidase activity as partial saturation of the antimycin-binding site with HQNO. (3) The extent of the rapid reduction of cytochrome b in the presence of excess antimycin is proportional to the percentage of intact Rieske Fe-S cluster. (4) The measured rate of oxidation of endogenous ubiquinol (V₂) by submitochondrial particles is dependent on the substrate used to reduce ubiquinone, especially at low levels of ubiquinone. (5) Pool-function kinetics in the oxidation of substrate, found both in the presence and absence of free ubiquinone, are due both to the pool of free ubiquinone and to direct collision between Q-loaded Q-reducing and -oxidizing enzymes. At infinite Q content only the former mechanism is operative; at low Q content only the latter. (6) Duroquinone can be reduced directly by NADH dehydrogenase without mediation of ubiquinone, but duroquinol cannot be oxidized in the absence of ubiquinone. On the other hand, the reduction of cytochrome b by duroquinol does not require the presence of ubiquinone. (7) It is suggested that the need for ubiquinone for the oxidation of duroquinol is due to the requirement of ubisemiquinone for the oxidation of cytochrome b, duroquinol not being able to form a stabilized semiquinone.     

Participation of angiotensin II in the establishment of negative emotional reactions

In waking rats and rabbits systemically injected angiotensin II was shown to participate predominantly in the mechanisms of negative emotional reactions. The effects of angiotensin II were observed at the behavioural level as well as at the neuronal one. Depending on the dose and the time of injection of angiotensin II and its specific antagonist saralasin they inhibited or facilitated elaboration and extinction of automatized conditioned active avoidance independently of arterial, pressure changes, the pain threshold being altered. Injection of angiotensin II abolished individual behavioural reactions of the animals in response to stress factors and increased their resistability to emotional stress. The negative emotional reactions were found to induce changes of chemosensitivity of neurones of the parafascicular complex of the medial thalamus and the midbrain reticular formation during microionophoretic application of angiotensin II. A supposition is made about the increase of angiotensin II brain synthesis under conditions of emotional stress.     

Succinate-ubiquinone reductase site of the respiratory chain

Data on succinate-ubiquinone reductase are critically reviewed. The structural and catalytic properties of succinate dehydrogenase and succinate-ubiquinone reductase are compared. The redox components, active centers and proteins involved in the enzyme interaction with ubiquinone are described. Some structural and kinetic features of the succinate-ubiquinone reductase as the respiratory chain component and feasible mechanisms of regulation of the succinate-ubiquinone reductase activity are discussed.