Channels in the gramicidin S-with-urea structure and their possible relation to transmembrane ion transport.

The structure of membrane-active antibiotic cyclodecapeptide gramicidin S in the crystals of its complex with urea, C(60)H(92)N(12)0(10).0.(5)[(NH(2))(2)CO].7.94H(2)0, has been investigated with three-dimensional X-ray data by the automatic sequential approximation method. The crystals are trigonal, space group P3(1)21, a = 25.80(3), c= 21.49 (2) A, M(r) = 7968, calculated density = 1.088 mg m(-3), Z = 1. Conventional R factor: R1 = 0.0943, wR2 = 0.2478 [I> 2sigma(I)]. The molecule possesses an antiparallel twisted beta-structure, with turns involving the Phe-Pro peptides. The Orn side chains extend on one side of the sheet, while the non-polar Val and Leu side chains are located on the other face. One of the Orn residues (namely Orn2) is linked by an intermolecular hydrogen bond to the O atom of Phe4 residue, the other is free. The side chains of the Phe residues have trans orientation (chi(1) approximately 180 degrees ) and those of the Val, Orn, Leu residues, except those of Orn2, have the preferential gauche orientation with the chi(1) angle close to 60. Two side chains show statistical disorder and conformation of the Pro residues is C(s)-C(beta)-exo. There is half a urea molecule and also 7.94 water molecules distributed on 13 positions for each antibiotic molecule. A partially occupied and poorly ordered alcohol molecule had been identified. The gramicidin S molecules are arranged around the 3(1) axis in the form of a left-handed double spiral forming suggestive channels. The outer hydrophobic surface of the spiral is made of uncharged side radicals while the inside surface consists of the main-chain atoms, mainly O and N, and of ornithine side chains with N atoms at the ends. By changing the Orn side-chain conformation, the inner diameter of the channels may change from 3.4 to 6.3 A. Thus, ions and particles of rather large size may pass through the channel. The possibility of the creation of the gramicidin S channels in mitochondrial membranes has been noted by some biochemists. The channel complexes are close-packed in a hexagonal arrangement in the crystal. The CI(-) ions, present in abundance in the mother solution, are not found ordered in the crystals, which may indicate the absence of the charges in the terminal N atoms of the Orn residues.

[Gramicidin channels: a new mechanism for transmembrane transfer of ions (from high resolution x-ray structural studies of the antibiotic)]. / Gramitsidinovye kanaly: novyi mekhanizm transmembrannogo perenosa ionov (po dannym rentgenostrukturnogo issledovaniia antibiotika s vysokim razresheniem).

The crystal structure of the membrane-active antibiotic-cyclopeptide gramicidin S complex with urea was determined by the X-ray structure analysis. The gramicidin S molecule possesses an antiparallel beta-structure, its slightly twisted 30-membered cycle has a roughly rectangular form about 4.8 x 13.6 A in size, with the lesser side being formed by the main chain atoms of Phe and Pro residues. The maximum size of the molecule is 22.9 A. A characteristic feature of the molecule is the position of the extended side chains of the Orn residues on one side of the molecular cycle in the form of peculiar "legs--tentacles". One of these legs is "fastened" by the intramolecular H-bond to O atom of the nearer Phe4 residue, the other being free. The distance between the terminal NE atoms of the Orn residues is 5.7 A. The side chains of the Phe and Orn2 residues have trans-orientation, those of the Val, Orn7, Leu residues gauche-orientation. For Val1 and Leu3 side chains statistical disorder of the terminal C atoms is realized. The pyrrolidine rings of the Pro residues adopt Cs-C beta-exo conformation. There are one urea and 20 water molecules per one antibiotic molecule in the structure. The positions of three water molecules are fully occupied, the others with the probability of 0.56-0.20. One of the "water" positions is occupied on 2/3 by water, and on 1/3 by the O atom of the alcohol. There is a complicated system of intra- and intermolecular H-bonds in the structure, with and without the participation of water, alcohol and urea molecules. The gramicidin S molecules, collecting around 3(1) axis according to the left-handed double helix, form the channels whose outside hydrophobic surface is built of the side uncharged radicals, the inside surface being built of the main chain atoms, mainly of the O and N atoms and of the ornithine "tails" with uncharged NE atoms at the termini. The outer diameter of the channel is 29-43 A, inner (without ornithine "tails") is about 12.7 A. At the expense of the change of these "tails" conformation, the inner diameter of the channel filled with water molecules may change from 3.4 up to 6.3 A. Thus, the ions and particles of a rather large size may pass through the channel. The gramicidin channels are discovered and described for the first time. The channels in the crystal structure are close-packed under the hexagonal law.(ABSTRACT TRUNCATED AT 400 WORDS)

[Characteristics of the electrolyte balance of the blood of healthy newborn calves and calves with diarrhea]. / Osobennosti élektrolitnogo balansa krovi novorozhdennykh teliat v norme i pri diaree.

Cows and newborn (just after the birth, and on the 1st, 3rd, 5th and 10th days after it) calves were tested for the peculiarities of the electrolyte blood composition and acid-base balance under normal and diarrheic conditions. The values of Na+/K+, Cl-/HCO3-, Pn/Ca2+ ratios in the blood serum of sick animals remain unchanged, which testifies to the deep disturbances of the water-salt metabolism in tissues.

[Effect of carbostimulin on acid-base equilibrium of the blood of racing horses during exertion]. / Vliianie karbostimulina na kislotno-shchelochnoe sostoianie krovi sportivnykh loshadei pri fizicheskoi nagruzke.

The paper deals with possibility to regulate in a proper direction the acid-base state in race horse blood administering carbostimulin at rest and under physical exercises. The preparation is shown to favour an increase in alkaline blood reserves in race hours at rest and to prevent acidotic changes caused by physical exercises. The results obtained show a promising use of carbostimulin for the directed correction of the acid-base state of blood in race horses aimed at increasing the efficiency of the training process.

[Effect of total content of carbon dioxide in blood biosynthesis of antipseudoplague antibodies in chickens]. / Vliianie obshchego soderzhaniia uglekisloty v krovi na biosintez protivopsevdochumnykh antitel u tsypliat.

The paper is concerned with a study of the sodium bicarbonate, carboxylin and hydrochloric acid effect on certain indices of acid-base balance in blood and on dynamics of antibody formation in chickens. The sodium bicarbonate or carboxylin feeding increases the carbon dioxide total content and intensity of antipseudoplague antibodies biosynthesis in the blood by 12-21 or 12.5-40%, respectively, as compared with the control. The hydrochloric acid feeding causes a decrease in the total amount of CO2 in the blood and inhibition of antibody formation by 12.7-32.8 % as compared with the control.

[State of acid-base balance in chickens and pigs in commercial livestock farms]. / Sostoianie kislotno-shchelochnogo ravnovesiia u kur i svinei v usloviiakh zhivotnovodcheskikh khoziaistv promyshlennogo tipa.

Experiments on chickens of different age groups (one day--1 months) from large poultry plants of the Kiev Region established that metabolic acidosis develops in chickens at the age of 10-30 days. Compensated alkalosis is observed in them at the age of two months and further. In chickens whose HCO3- level in blood is 15-18 mM/l the content of uric acid in the liver and blood increases as compared to the control (HCO3- --23 mM/l); they also differ in a high intensity of the growth. A rise of the HCO3- concentration in chicken blood up to 33 mM/l favours a still greater decrease in the level of uric acid in tissues and an increase in the chicken growth intensity as compared to the control. Studies in the state of the blood acid-base balance in pigs of the commercial complex "Kalityansky" showed that compensated alkalosis develops in the whole pig stock.