Gene copy number effects in the mer operon of plasmid NR1.

The level of resistance to Hg2+ determined by the inducible mer operon of plasmid NR1 was essentially the same for three gene copy number variants in Escherichia coli, less in Proteus mirabilis, and intermediate in P. mirabilis "transitioned" to a high r-determinant gene copy number. Cell-free volatilization rates of radioactive mercury indicated increasing levels of intracellular mercuric reductase enzyme from low- to high-gene copy number forms in P. mirabilis and from low- to high-copy number forms in E. coli, but the additional enzyme in E. coli was effectively cryptic.     

Adenosine 3':5'-monophosphate-mediated inhibition of myosin light chain phosphorylation in bovine aortic actomyosin.

Ca2+-dependent phosphorylation of the myosin light chains in bovine aortic native actomyosin is markedly depressed in the presence of cyclic AMP and its dependent protein kinase. This inhibition occurs with either cardiac, skeletal, or aortic protein kinase plus cyclic AMP, while little or no inhibition occurs with either cyclic AMP or protein kinase alone. The extent of inhibition is related to the concentration of protein kinase and approaches a maximum of approximately 50%. Concomitant with the inhibition of myosin light chain phosphorylation is (a) an increased phosphorylation of a 100,000-dalton moiety which possibly corresponds to the myosin light chain kinase present in the native actomyosin preparation and (b) a decrease in the actomyosin Mg2+-ATPase activity. These findings suggest that modulation of actin-myosin interactions by the cAMP system directly at the level of the contractile proteins may represent a mechanism by which beta adrenergic relaxation occurs in mammalian vascular smooth muscle.     

Biological Dinitrogen Fixation (Acetylene Reduction) Associated with Florida Mangroves

Biological dinitrogen fixation in mangrove communities of the Tampa Bay region of South Florida was investigated using the acetylene reduction technique. Low rates of acetylene reduction (0.01 to 1.84 nmol of C₂H₄/g [wet weight] per h) were associated with plant-free sediments, while plant-associated sediments gave rise to slightly higher rates. Activity in sediments increased greatly upon the addition of various carbon sources, indicating an energy limitation for nitrogenase (C₂H₂) activity. In situ determinations of dinitrogen fixation in sediments also indicated low rates and exhibited a similar response to glucose amendment. Litter from the green macroalga, Ulva spp., mangrove leaves, and sea grass also gave rise to significant rates of acetylene reduction.     

Optical measurements of intracellular oxygen concentration of rat heart in vitro

The optical characteristics of hemoglobin-free perfused rat heart have been examined in detail. Ethyl hydrogen peroxide is found to convert myoglobin into “ferryl compound” in the perfused heart, as is also seen in vitro. After pretreatment with ethyl hydrogen peroxide, a typical mitochondrial absorption spectrum, similar to that of isolated rat heart mitochondria, is obtained in perfused heart. The overall absorption spectrum of the heart obtained by the aerobic to anaerobic transition is a superposition of the mitochondrial spectrum on that of myoglobin. By comparing these spectra, it is found that measurement of cytochrome a + a₃ at 605–620 nm is possible in spite of the absorbance change due to the oxygenation-deoxygenation of myoglobin, whereas the wavelength pairs for cytochrome c at 550-540 nm, cytochrome b at 562–575 nm and cytochrome a + a₃ at 445–450 nm can not be used in the heart because of interference from the absorption change of myoglobin. The partial pressure of O₂ (P₅₀) which is required for half maximal deoxygenation (or oxygenation) of myoglobin in perfused heart is found to be 2.4 mm Hg at room temperature and the Hill constant, n, is 1.1; these values are similar to those of myoglobin purified from rat heart. The steady-state O₂ titration has been performed by using absorbancy changes of myoglobin and cytochrome a + a₃ as intracellular O₂ indicators. In the perfused heart, the percentage change of oxygenation-deoxygenation of myoglobin parallels the oxidation-reduction of cytochrome a + a₃, while the mixture of purified myoglobin and isolated mitochondria shows a deviation, reflecting the difference of O₂ affinities between myoglobin and cytochrome a + a₃. The results indicate that there may be an O₂ gradient between cytosolic and mitochondrial compartments in the hemoglobin-free perfused heart. The absorption changes of myoglobin and of cytochrome a + a₃ can be measured in a single contraction-relaxation cycle. A triple beam method was introduced to eliminate the effect of light scattering changes in these measurements. The results demonstrated that myoglobin is more oxygenated during the systolic and diastolic periods and deoxygenated in the resting period, whereas cytochrome a + a₃ is more reduced in systole and diastole and oxidized in the resting state. Changing the perfusion conditions greatly alters the time course of the events which occur during the contraction-relaxation cycle of the perfused heart.     

Effects of amino acids on Thiobacillus acidophilus. I. Growth studies with special reference to valine.

The heterotrophic growth of Thiobacillus acidophilus was inhibited by branched-chain amino acids; valine, isoleucine, and leucine. The inhibition by valine and leucine were partially reversed by isoleucine, and the inhibition by isoleucine was partially reversed by valine. Inhibitions by methionine or threonine were partially reversed when both amino acids were present in the growth medium. Inhibition by tyrosine was increased by phenylalanine or tryptophan. Cystine completely inhibited growth. Other amino acids tested produced little or no inhibition. Acetohydroxy acid synthetase (AHAS) activity was demonstrated in crude extracts of T. acidophilus. In crude extracts the optimum pH was 8.5 with a shift to 9.0 in the presence of valine. Valine was the only branched-chain amino acid which inhibited the AHAS activity. The presence of only one peak of AHAS activity upon centrifugation in linear glycerol density gradients demonstrated that the AHAS activity sediments as one component.     

Production and characterization of antisera against three individual NHC proteins; a case of a generally distributed NHC protein

In order to assess the selectivity of the distribution patterns of individual nonhistone chromosomal proteins (NHC proteins), immunofluorescent staining experiments were performed on Drosophila polytene chromosomes. Antisera have been prepared against three individual NHC proteins which were isolated by sequential preparative slab gel isoelectric focusing and SDS polyacrylamide gel electrophoresis. In two cases, immunofluorescent staining of the chromosomes indicated a specific limited distribution pattern; apparently the antigen in each case is present at a reproducible and distinct subset of chromomeres. This type of pattern has also been obtained with antisera prepared against molecular weight subfractions of NHC proteins (Silver and Elgin, 1977). Each selective fluorescence distribution pattern obtained so far is reproducible and unique to the antiserum under study. In a third case, an antiserum caused prominant staining at dense chromomeres and the chromocenter in a pattern mimicking DNA (and presumably histone) distribution. Indirect radioimmunostaining of SDS and isoelectric focusing gels on which total NHC proteins had been separated confirmed that this antiserum reacted specifically with a protein(s) of molecular weight 21,000 D and pI 5.2. The data in conjunction with absorption experiments indicates that the chromosomal staining is due to an interaction of antibodies with NHC protein(s) and not with histones. This finding suggests that at least one major acidic NHC protein plays a very general role (comparable to that of the histones) in maintaining chromatin structure.     

Species variation in the distribution of cholinesterases in the ovary of the plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer

Synopsis Sections of ovary from plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer have been histochemically processed to demonstrate acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in nervous and non-nervous tissue. The effects of different reproductive states on enzyme activity were observed in some animals. AChE-containing nerves were sparse in rabbit and rat but plentiful in cat and roe deer. Nerves containing BuChE were not detectable in ferret or guinea-pig and were rare in cat. Species variations in the activity and type of enzyme were also found in non-neuronal tissues. Some blood vessels in the ovaries of guinea-pig and viscacha contained AChE. No other species showed a reaction for AChE in non-neuronal stromal tissue but BuChE was present at this site in all animals except rat. Granulosa cells reacted for AChE only in cat and rabbit while luteal cells were reactive in cat, rabbit and roe deer. Some BuChE activity was present in granulosa and or luteal cells in all species except roe deer. In rat, BuChE activity in luteal cells increased during oregnaney and the early phase of pseudopregnancy. The difficulty of assigning a function to ovarian cholinesterases is discussed.     

Microbiological leaching of a chalcopyrite concentrate by Thiobacillus ferrooxidans

The microbiological leaching of a chalcopyrite concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. The optimum leaching conditions regarding pH, temperature, and pulp density were found to be 2.3, 35°C, and 22%, respectively. The energy of activation was calculated to be 16.7 kcal/mol. During these experiments the maximum rate of copper dissolution was about 215 mg/liters/hr and the final copper concentration was as high as 55 g/liter. This latter value is in the range of copper concentrations which may be used for direct electrorecovery of copper. Jarosite formation was observed during the leaching of the chalcopyrite concentrate. When the leach residue was reground to expose new substrate surface, subsequent leaching resulted in copper extractions up to about 80%. On the basis of this experimental work, a flow sheet has been proposed for commercial scale biohydrometallurgical treatment of high-grade chalcopyrite materials.     

Processing of vibratory and acoustic signals by ventral cord neurones in the cricket Gryllus campestris

The responses of single vibratory receptors and ascending ventral cord interneurones were studied extracellularly in Gryllus campestris L. The physiology of the vibration receptors resembled those found in tettigoniids and locusts. The frequency responses of the subgenual receptors provide two possible cues for central frequency discrimination: differences in mean tuning between groups of receptors in the different leg pairs and a range of receptors tuned to different frequencies within one subgenual organ.Most of the ascending vibratory interneurones were highly sensitive in either the low or high frequency range. Broadbanded neurones were less sensitive. The characteristic sensitivity peaks of these units are due mainly to receptor inputs from a particular leg pair, although most central neurones receive inputs from all 6 legs. Only one neurone type, TN1 received excitatory inputs from both auditory and vibratory receptors; its responses were greatly enhanced by the simultaneous presentation of both stimulus modes. The responses to sound stimuli of AN2, on the other hand, were inhibited by vibration. No other auditory interneurones investigated were influenced by inputs from vibration receptors. Central processing of vibratory information in the cricket is compared with that of tettigoniids and locusts.