Stoichiometry of microsomal oxidation reactions. Distribution of redox-equivalents in monooxygenase and oxidase reactions catalyzed by cytochrome P-450

The stoichiometry of NADPH oxidation in rabbit liver microsomes was studied. It was shown that in uncoupled reactions cytochrome P-450, besides O2- generation catalyzes direct two- and four-electron reduction of O2 to produce H2O2 and water, respectively. With an increase in pH and ionic strength, the amount of O2 reduced via an one-electron route increases at the expense of the two-electron reaction. In parallel, with a rise in pH the steady-state concentration of the oxy-complex of cytochrome P-450 increases, while the synergism of NADPH and NADH action in the H2O2 formation reaction is replaced by competition. The four-electron reduction is markedly accelerated and becomes the main pathway of O2 reduction in the presence of a pseudo-substrate--perfluorohexane. Treatment of rabbit with phenobarbital, which induces the cytochrome P-450 isozyme specific to benzphetamine results in a 2-fold increase in the degree of coupling of NADPH and benzphetamine oxidation. The experimental results suggest that the ratio of reactions of one- and two-electron reduction of O2 is controlled by the ratio of rates of one- and two-electron reduction of cytochrome P-450. In the presence of pseudo-substrates cytochrome P-450 acts predominantly as a four-electron oxidase; one of possible reasons for the uncoupling of microsomal monooxygenase reactions is the multiplicity of cytochrome P-450 isozymes.     

Responses of receptive fields of frog retinal ganglion cells to the leading and trailing edges of moving stimuli

The position of on- and off-discharge centers in class 1 and 3 receptive fields of the frog retina was determined with the aid of moving bars of different lengths. On- and off-centers of receptive fields of the first group coincide, those of the second are spatially separate, and in fields of the 3rd group the discharge center of one contrast sign occupies the central position and discharge centers of the opposite sign are located at the periphery, to its right and left. Receptive fields of the frog retina thus have features which approximate them to the concentric receptive fields of geniculate neurons and the fields of the cat visual cortex. Asymmetry in the responses was found: during movement in opposite directions the distance between the discharge centers changed, during movement to one side only one of the peripheral centers was revealed, whereas during movement to the other side the second center was revealed on the opposite side of the receptive field. This asymmetry of spatiotemporal relations in the receptive fields is similar to that found in the fields of cortical neurons and is connected with their directional properties.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 75–85, January–February, 1980.     

Restoration of morphological and functional integrity in the regenerating eye of the giant African land snail Achatina fulica

To determine whether vision returns to its original state following eye removal in Achatina fulica, light and electron microscope examinations, electrophysiological recordings and behavioural tests were carried out on the regenerating snails. Reparative morphogenesis can result in the restoration of the peripheral sense organ even in the absence of complete regrowth of the tentacle, but it can also lead to the formation of aberrant regenerates. We found that anatomically and ultrastructurally the eyes of the ‘most normal’ regenerates were basically the same as the original eyes. Under normal conditions each eye is composed of a principal and an accessory eye, both sharing a common cornea. The only difference between regenerated and native eyes is the smaller size of the former, as a result of a reduced number of retinal cells. Electroretinographic responses revealed that the molecular mechanism of phototransduction is restored, in principle, but that flicker fusion frequency in the regenerated eye is significantly lower than in the normal eye. The directional movement to a visual stimulus (a black stripe of 45° width) had not completely recovered even 6 months after amputation. This suggests that the central projections of the optic nerve had not become fully re‐established at the time of testing.     

The reactivity of the hypophyseal-adrenal system in rats with different forms of adaptive behavioral pathology]

The dexamethasone suppression test (DST) was applied to male Wistar rats with different models of depression: group with the learned helplessness, group with informational neurosis provided by time-deficit conditioned avoidance training, as well as groups of rats of two strains selected for low (KLA)--and high (KHA) avoidance learning. The pre-dexamethasone basal and stress-induced corticosterone levels were similar in intact rats and those exposed to inescapable shock. The dexamethasone administration (5 mkg/kg) failed to decrease the serum corticosterone level in rats with learned helplessness. The informational neurosis increased significantly the basal corticosterone level and decreased the stress response. Serum corticosterone levels were similar in KLA and KHA rats. These results give evidence that two stress-induced rat models of depression with similar behavioural disturbances (reduction of escape/avoidance reactions) exhibit marked differences in the activity of hypothalamo-pituitary-adrenal (HPA) axis.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

Study of the structure of colonies of active and inactive Actinomyces parvullus variants using luminescence and scanning microscopy]

The colony structure of the active and inactive proactinomycete-like variants of Actinomyces parvullus producing actinomycin D was studied with luminescent and scanning microscopy. Clear differentiation of the colony profile was shown by the structure and functions of the mycelium layers. A zone of active synthesis and accumulation of the antibiotic was observed in the colonies of the active variant in the upper part of the substrate mycelium with reddish-yellow self luminescence in UV light and characteristic close hyphae "cemented" by the intracellular substance. Formations of the granule type were often noted on the hyphae of that layer. The layer of the aerial mycelium was loosely connected with the substrate mycelium and consisted of sporophores and spore chains partially broken into single spores. The colonies of the inactive proactinomycete-like variant had a slightly differentiated profile with a sponge-like structure, no zones of the antibiotic synthesis being found. The presence of the intracellular substance was observed in the upper part of the colony supersubstrate mycelium.     

Growth and oxidation of sulfur compounds by Thiocapsa roseopersicina in darkness]

The purple sulphur bacterium Thiocapsa roseopersicina, strain BBS, grown in the darkness in aerobic autotrophic conditions, oxidized sulphides to free sulphur and then to sulphates. This was accompanied with the fixation of carbon dioxide by the cells. Addition of glucose to the mineral medium increased the biomass yield; the cells oxidized thiosulphate still at a high rate. These results prove the possibility of switching T. roseopersicina from photosynthesis to a dark chemolithautotrophic way of life.     

Identification and characteristics of plasmids of the strains of erythromycin-producing Streptomyces erythreus

Presence of plasmid DNA was investigated in laboratory strains 2 and 4 (NRRL 2338) of S. erythreus, as well as in strains 1 and 3 of S. erythreus subjected to improvement with respect to erythromycin production. Families of plasmids close by their molecular weights were identified in S. erythreus strains 3 and 4 (NRRL 2338). A plasmid DNA fraction of S. erythreus strain 3 was studied with electron microscopy. It enabled to identify 5 plasmids: pSE11, pSE12, pSE13, pSE14 and pSE15 with length of 5.3, 12.4, 16.3, 29.6 and 86.9 kb respectively. Using of various procedures for isolation of extrachromosomal DNA did not provide its detection in S. erythreus strains 1 and 2. At least a part of the plasmids detected in S. erythreus strains 3 and 4 (NRRL 2338) was conjugative. 32R-Labeled plasmid DNA of S. erythreus strain 3 was subjected to hydridization according to Sauthern with total DNA of the 4 strains treated with restrictases BamHI, PstI and BgIII. The studies showed that the genome of S. erythreus strain 2 was not homologous with the probe while S. erythreus strain 1 contained one of the plasmids or its part in chromosome-integrated state. In strains 3 and 4 (NRRL 2338) of S. erythreus certain plasmid DNAs were present in both autonomous and chromosome-inserted states. 32P-Labeled gene of erythromycin resistance (ermE) was subjected to hybridization according to Southern with total DNA of the 4 strains and with DNA plasmid fraction of S. erythreus strain 3. The signal was positive only in hydridization of the probe with total DNA of S. erythreus strains 1, 3, and 4 (NRRL 2338).(ABSTRACT TRUNCATED AT 250 WORDS)