Different families of double-stranded conformations of DNA as revealed by computer calculations

An algorithm has been developed that permits one to find all possible conformations of the sugar-phosphate backbone for any given disposition of DNA base pairs. For each of the conformations thus obtained, the energy of the helix was calculated by the method of atom-atom potentials. Several isolated regions in the space of the bases′ parameters (Arnott's parameters) have been found for energetically favorable helical structures. Two parameters, the distance of a base pair from the helix axis, D, and the windling angle, τ, allow one to subdivide possible conformations into the families of closely related forms. Two regions (ravines) on the (D, τ) map correspond to the know A and B families. In the B family a continuous transition has been obtained in which the double helix undergoes increasing winding, while the base pairs are moving toward the major (nonglycosidic) groove. Interrelationships between the variables, characterizing the spatial structure of the double helix, D, τ, TL and χ, when going along the bottom of the B ravine, were also obtained. Besides the Known A and B families, several new ones were found to be energetically possible. Among these the strongly underwound helices with the negative D values, as well as the forms with the C4-C5 angle in a trans position, should be mentioned. Biological roles of the different double-stranded conformations, in particular, in protein-nuclei acid interaction are discussed.     

On structure and functioning of ecosystem in a Salmon lake

The seasonal dynamics of the main components of the ecosystem as well as the vertical distribution of their biomass and production were studied in the salmon lake Dalnee at Kamchatka Peninsula. The data received were used for the construction of schemes of energy balance during two successive years: 1970 and 1971, which were different by their thermic regime. Analysis of schemes showed that during a colder season the food chain was shorter and more effective in relation of the use of primary production by zooplankton. Through the detritus pool the ecosystem used from 16% (1971) up to 70% (1970) of energy of primary production. Seasonal succession includes two main phases -autotrophic and heterotrophic. The energy balance of the planktonic community at these two phases is given.     

Coordination of arm movement during locomotion in ophiurans

During movement of the ophiuranAmphipholis kochii Lutken, any one of its arms can point forward and, consequently, any arm can perform different functions. The arm, when separated from the ophiuran together with the adjacent part of the nerve ring, is capable of complex motor acts, including locomotion. Division of the nerve ring in the ophiuran disturbs coordination of the arms. The results of experiments in which one or more arms were amputated showed that the choice of leading arm and of method of locomotion depends mainly on afferent impulses received from the arms. The results indicate that the neural centers of individual arms possess relative autonomy. Coordinated working of the centers is achieved through their interaction. This interaction ensures the distribution of functions between the arms in accordance with the motor task to be undertaken and coordinates the activity of the arms in time. The dominant role in the distribution of functions between the arms is played by the center of the leading arm, which controls the activity of at least the adjacent centers.Institute of Oceanology, Academy of Sciences of the USSR, Moscow. Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Moscow State University. Translated from Neriofiziologiya, Vol. 8, No. 5, pp. 529–537, September–October, 1976.     

A new method for determination of elastolytic activity using (14C) labeled elastin and its application to leukocytic elastase.

A new, highly sensitive and specific assay for elastolytic activity is described which employs insoluble elastin randomly labeled with [¹⁴C]. The substrate was prepared by labeling amino groups of the protein in vitro with [¹⁴C] methyl groups by reductive alkylation. The substrate was used to quantitate elastolytic activity from human leukocytes and to compare leukocytic elastase with pancreatic elastase. Purified human leukocytic elastase was approximately one-fourth as active as pancreatic elastase. Similar difference between leukocytic elastase and pancreatic elastase activities was found when the enzymes were tested against succinyl-L-alanyl-L-alanyl-L-alanine-p-nitroanilide, but not when t-BOC-L-alanine-p-nitrophenyl ester was used.     

A trypsin-resistant heme peptide from cardiac cytochrome c1.

A tryptic resistant heme peptide has been prepared and purified from cardiac cytochrome c1. This purified peptide is not further hydrolyzed by reactions of other proteolytic enzymes, such as pronase. The peptide contains 2 residues each of serine, cysteine and valine, and 1 residue each of alanine, methionine, tyrosine, histidine, arginine, proline, glutamic acid (glutamine) and aspartic acid. The intensity of the absorption spectrum of the peptide has been found to be dependent upon, but the positions of the absorption maxima do not vary with, concentration. The heme peptide does not show multiple splitting of absorption peaks at liquid N2 temperatures as does the intact cytochrome C1. However, cyanide rapidly reacts with the peptide and causes significant spectral changes. CD spectra of the peptide exhibit a typical profile of a non-structured heme peptide with positive CD bands in the Soret region and around 250 nm, and a broad negative extreme of 320-360 nm. The similarities and differences between the tryptic resistant heme peptides from cytochromes c1 and c have been compared.     

Interaction of flavins with electron-rich metals.

A complex of the electron-rich ion Cu(I) with the flavoquinone analogue 10-methylisoalloxazine has been synthesized and characterized by x-ray methods. The complex is unstable to oxygen. It is black-green in color, in contrast with the bright yellow, orange, or orange-brown crystalline complexes of 10-methylisoalloxazine or riboflavin with Cu(II), Ag(I), and Pb(II). These results are indicative of strong perturbation of the flavin electronic structure by the Cu(I) ion and suggest that this complex is a reasonable model for incipient transfer of an electron from a reduced metal to flavoquinone. the crystal structure is orthorhombic, Pna2-1, with unit cell constants a = 31.24(1) (figures in parentheses are estimated standard deviations), b = 12.862(4), c = 6.239(2) A, Pobs = 1.76 g per cm-3 and Pcalc = 1.77 g per cm-3 for Z = 4 and asymmetric formula CuClO4-2(C11H8N4O2). HCOOH. The final R factor based on 1250 counter-measured data is 8.8%. The 2 independent 10-methylisoalloxazine molecules, A and B, bind strongly to the cuprous ion throug N(5) of each flavin. The copper is approximately linearly coordinated with an N-Cu-N angle of 153(1) degrees, and Cu-N(5) distances of 1.94(2) A and 1.92(2) A. The next nearest atoms to Cu are the O(4) oxygens of each flavin, forming weak bonds with distances Cu-O(4) = 2.27(2) A and 2.21(2) A for molecules A and B. The dihedral angle between the 2 10-methylisoalloxazine molecules is 65.4 degrees.     

Nonsynaptic membrane of retinal horizontal cells as a slow potential amplifier

A simplified model of the membrane of horizontal cells of the L-type is designed to reflect two principal features of these cells previously studied experimentally: 1) their hyperpolarization response to light is the result of a decrease in the EPSP that is kept constant in darkness; 2) the resistance of their nonsynaptic membrane is reduced during hyperpolarization within physiological limits (from 0 to−70 mV). The model also reproduces properties of the horizontal cells such as the low membrane potential in darkness, reversal of the response to light during depolarization beyond the zero level, mutual amplification of color signals, saturation of the response to bright light, steady-state volt-ampere characteristics in darkness and light, and the amplitude characteristic curve which often has a steep part within a certain range of membrane potentials. The presence of hysteresis loops of the volt-ampere and amplitude characteristic curves of the horizontal cells predicted by the model was confirmed experimentally on the fish retina. Analysis of the model and results obtained with it show that the nonsynaptic membrane of the horizontal cells can actively amplify slow graded potentials.