Kinetic aspects of macroscopic fluctuations in solutions of liver alcohol dehydrogenase

Kinetic analysis of macroscopic fluctuations in alcohol dehydrogenase reaction was carried out. The integral form of Michaelis-Menten equation was used. It is shown that reaction rate fluctuations to be observed in experiment are connected with kinetic constants of relative affinity of ADG to NAD and NAD X H.     

Microbial Transport, Survival, and Succession in a Sequence of Buried Sediments

Abstract Two chronosequences of unsaturated, buried loess sediments, ranging in age from <10,000 years to >1 million years, were investigated to reconstruct patterns of microbial ecological succession that have occurred since sediment burial. The relative importance of microbial transport and survival to succession was inferred from sediment ages, porewater ages, patterns of abundance (measured by direct counts, counts of culturable cells, and total phospholipid fatty acids), activities (measured by radiotracer and enzyme assays), and community composition (measured by phospholipid fatty acid patterns and Biolog substrate usage). Core samples were collected at two sites 40 km apart in the Palouse region of eastern Washington State, near the towns of Washtucna and Winona. The Washtucna site was flooded multiple times during the Pleistocene by glacial outburst floods; the Winona site elevation is above flood stage. Sediments at the Washtucna site were collected from near surface to 14.9 m depth, where the sediment age was approximately 250 ka and the porewater age was 3700 years; sample intervals at the Winona site ranged from near surface to 38 m (sediment age: approximately 1 Ma; porewater age: 1200 years). Microbial abundance and activities declined with depth at both sites; however, even the deepest, oldest sediments showed evidence of viable microorganisms. Same-age sediments had equal quantities of microorganisms, but different community types. Differences in community makeup between the two sites can be attributed to differences in groundwater recharge and paleoflooding. Estimates of the microbial community age can be constrained by porewater and sediment ages. In the shallower sediments (<9 m at Washtucna, <12 m at Winona), the microbial communities are likely similar in age to the groundwater; thus, microbial succession has been influenced by recent transport of microorganisms from the surface. In the deeper sediments, the populations may be considerably older than the porewater ages, since microbial transport is severely restricted in unsaturated sediments. This is particularly true at the Winona site, which was never flooded.     

Evoked activity in the ventral horn of the lumbar segments of the spinal cord during cortical inhibition of cortical motor responses

Electrical activity in the flexor nerve and focal potentials (FP) in the medial and lateral zones of the ventral horn (VH) of segments L₆ and L₇ of the spinal cord, evoked by excitation of the contralateral motor cortex, were recorded in delicate experiments on cats. These focal potentials were studied during inhibition of the flexor response that developed as a result of prior excitation of the ipsilateral cortex ("cortical inhibition"). During the inhibition the FP's of the medial zone (layer VIII, according to Rexed) were greatly increased, mainly in their negative components, their time-characteristics being altered. When the interval between excitations was 50 msec (in that case the inhibition was most pronounced) the medial FP's arose against a negative background, which was a late component of the previous activity evoked by conditioning excitation. The appearance of this late component was correlated with the development of inhibition of the cortical flexor response. At the same time a positive condition developed in the lateral zone, in the region of the nucleus biceps-semitendinosus, which indicated orientation in a lateral direction of the interneurons discharging in the medial zone at late periods after the conditioning excitation. Inhibition of the flexor response was accompanied by depression of the lateral FP's without change in their sign or in the time-structure of their components. It is suggested that cortical inhibition of the cortical flexor response arises at the interneuron level. The functional structure of that inhibitory pathway is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 185–193, March–April, 1971.     

Convergence of synaptic influences of contralateral somatic afferents on interneurons in segmental inhibitory pathways to motoneurons

Convergence of contralateral somatic afferent synaptic influences on segmental inhibitory neurons was investigated by intracellular recording of postsynaptic potentials of -motoneurons in experiments on cats. Excitatory synaptic influences of afferents of the contralateral flexor reflex were shown to converge on interneurons of both segmental inhibitory systems studied: afferents of flexor reflex and group Ia muscle afferents. Interneurons of inhibitory systems are exposed not only to excitatory but also to inhibitory contralateral influences. Contralateral inhibitory PSPs of montoneurons are produced through ipsilateral inhibitory systems; a leading role is played by inhibitory neurons of the flexor reflex system of afferents. Inhibitory neurons of the Ia system as a rule do not make an important contribution to generation of contralateral IPSPs.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 476–484, September–October, 1973.     

Deviation from a Poisson distribution in a series of identical tests of E. coli cultures as a result of the effect of correlating factors of exo- and endogenous natures]

Vital cells number (VCN) in the sampling of E. coli populations was experimentally measured and distribution histograms were obtained. In most cases distributions show considerable deviation from Poisson model. VCN distribution histograms are polymodal, dispersion/arithmetical mean ratio may essentially differ from 1. The more essential differences from Poisson distribution were observed for populations with the higher cell concentration. Computer simulation of the VCN histograms indicated that additional parameters (such as those describing cellular interaction of different nature and/or other factors that influence random behaviour of cells) should be introduced into Poisson model to explain observed variations in VCN distribution histograms.     

DNA Bearing Bulky Fluorescent and Photoreactive Damage in Both Strands as Substrates of the Nucleotide Excision Repair System

Model DNA molecules that contain bulky lesions in both strands have been created, and their properties as substrates of the nucleotide excision repair (NER) system have been analyzed. The modified nucleoside, 5-[3-(4-azido-2,3,5,6-tetrafluorobenzamido)-1-propoxypropyl]-2′-deoxycytidine (dC^FAB), or the nonnucleoside fragment, N-[6-(9-anthracenylcarbamoyl)hexanoyl]-3-amino-1,2-propanediol (nAnt), have been inserted as damage in certain positions of the first DNA strand (“0”). The position of N-[6-5(6)- fluoresceinylcarbamoyl]hexanoyl]-3-amino-1,2-propanediol (nFlu) has been varied within the second DNA strand. This residue has been located opposite the removable damaging fragment of the first strand at positions–20,–10,–4, 0, +3, and +8 relative to the first lesion). It has been demonstrated that the presence of nFlu at the–4, 0, or +3 position of the second strand significantly reduces the thermostability of DNA duplexes, especially in the case of nAnt-DNA and completely excludes the possibility of NER-catalyzed excision from dC^FAB- and nAnt-containing 137-meric DNA with the second lesion at these positions. The introduction of nFlu at positions–20,–10, or +8 differently affects the excision efficiency of dC^FAB- and nAntcontaining fragments from the first strand. The excision efficiency of dC^FAB-containing fragments from extended double-damaged DNA is as high as from DNA that contains a single dC^FAB damage, while the excision of nAnt-containing fragments occurs with 80–90% lower efficiency from double-damaged DNA occurs from DNA that contains the single nAnt insert. The nFlu insert differently affects the interaction of the sensory XPC-HR23B dimer with dC^FAB- and nAnt-containing DNAs, although in all cases, this interaction occurs with increased efficiency compared to that with single-damaged DNAs. No direct correlation between the thermostability of the DNA duplex and XPC-DNA affinity on the one hand, and the excision efficiency of lesions on the other hand has been shown. The absence of the correlation may be caused by both functional features of variable multiprotein complexes involved in the recognition and verification of damage during NER and the sensitivity of the complexes to the structure of the damage and damage-surrounding DNA. The results are important for understanding the NER mechanism of elimination of bulky damage located in both DNA strands.     

Developmental features of the brain bioelectrical activity in children with remote consequences of a perinatal lesion of the CNS. II. EEG typology in normal and mental disorders

This research represents EEG - investigation by children with remote consequences of perinatal CNS pathology. Its described the different EEG types in normal and mental disorders in children. Its showed a early EEG - markers of abnormal ontogenesis in longitudinal study. The data obtained gives to prevent a negative dynamic of mental and speech development (learning disability, motor alalia, autism).     

Structural basis for the substrate specificity of tobacco etch virus protease

Because of its stringent sequence specificity, the 3C-type protease from tobacco etch virus (TEV) is frequently used to remove affinity tags from recombinant proteins. It is unclear, however, exactly how TEV protease recognizes its substrates with such high selectivity. The crystal structures of two TEV protease mutants, inactive C151A and autolysis-resistant S219D, have now been solved at 2.2- and 1.8-A resolution as complexes with a substrate and product peptide, respectively. The enzyme does not appear to have been perturbed by the mutations in either structure, and the modes of binding of the product and substrate are virtually identical. Analysis of the protein-ligand interactions helps to delineate the structural determinants of substrate specificity and provides guidance for reengineering the enzyme to further improve its utility for biotechnological applications.     

Field potentials in the lumbar ventral horn during combined extrapyramidal and cortical stimulation

Field potentials arising in the medial (Rexed's layer VIII) and lateral (region of the flexor motoneuronal nuclei) zones of the ventral horn during stimulation of the motor cortex or ventromedial funiculus in the cervical spinal cord were recorded in experiments on cats. Inhibition of the electrical response in the flexor nerve to stimulation of the contralateral cortex, an indicator of the cortical motor response, can be evoked by stimulation not only of the symmetrical point of the opposite cortex but also of the group of fibers of the ventromedial funiculus connected functionally with that point. In each experiment the fact that these fibers belonged functionally to the system conducting cortically evoked descending influences was verified in each experiment from a combination of specific criteria. Extrapyramidal inhibition of the cortical motor response is accompanied by the same changes in field potential in the medial and lateral zones of the ventral horn as cortical inhibition: by an increase in negativity in the first and by its suppression in the second. The differences between the two types of interaction are concerned chiefly with the temporal course of all the processes studied. The results are used as evidence of the extrapyramidal nature of cortical inhibition of the cortical motor response.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 597–607, November–December, 1972.     

Structural polymorphism of the liquid-crystalline dispersions formed from the double-stranded DNA molecules complexed with synthetic polycations

The double-stranded, linear DNA molecules form the liquid-crystalline dispersions (LCD) in water-salt solutions containing positively charged polyconidin molecules. It was established from the analysis of the absorption spectra of the LCDs formed from (DNA-polyconidin) complexes, that the mean size of the particles of these dispersions is equal to -6000 angstroms. The small-angle X-ray data show, that in the LCD particles different density of packing of the (DNA-polycation) complexes is realized. The comparison of the X-ray data of the liquid-crystalline phases of (DNA-polyconidin) complexes formed under various conditions with the phase diagram, that reflects the polymorphism of the linear double-stranded DNA liquid crystals, demonstrates that the hexagonal mode of the LCD packing is existing in 0.15-0.4 M NaCl solutions, whereas in 0.4-0.55 M NaCl solutions-- the cholesteric one. As a result of specific spatial organization the cholesteric LCD possesses of an abnormal optical activity in the CD spectrum. The similar situation takes place in the case of another synthetic polycation--poly(2,5-ionen), whose chemical structure differs from that of polyconidin. Thus, the structural polymorphism of the (DNA-polyconidine) LCDs was evidenced. It means that change of NaCl concentration opens a gate to control the spatial packing of the molecules of (DNA-polycation) complexes in the particles of LCDs. The supposition about mechanism of formation of the DNA cholesteric liquid-crystalline state in the narrow interval of NaCl concentrations was suggested.