Interference by Tris buffer in the estimation of protein by the Lowry procedure

Tris buffers were found to distort the measurement of protein by the Lowry method both by decreasing chromophore development with protein and by contributing blank color. Tris at an assay concentration of 0.37 mm markedly affects measured results. Similar Tris effects were observed at all wavelengths between 450 and 800 nm and with diverse protein samples. The distortion due to Tris is not correctable by simple blank correction, but it can be overcome by incorporating the same amount of Tris in the standards used. The distortion at Tris concentrations <0.15 mm appears to be within tolerable limits. No interference or distortion was observed with sodium phosphate buffer to an assay concentration of 40 mm. An automated Lowry procedure is also presented which gives excellent correlation with the manual method and an average coefficient of variation of <4%.     

Induction by the endoderm in birds

Ohne Zusammenfassung     

Retention of nutrients by the different wastes produced by the kaolin mining industry in Cornwall

Summary The chemical composition and leaching loss of applied fertilizers were measured from four waste materials derived from china clay extraction. Two waste materials, overburden and mica, had a higher nitrogen and calcium concentration, and were more efficient than sand wastes for the retention of these elements when applied as fertilizers. The possibility of using overburden and mica wastes as amendments for sand waste reclamation is briefly discussed.     

Alteration by mutation of the control by oxygen of the nar operon in Escherichia coli

Summary A nar-lac operon fusion was used to isolate a mutant in which the expression of the nar operon was no longer repressed by oxygen. The nar ^d mutation, located upstream of the nar structural genes, was found to be cis dominant; it led to independence from the Fnr protein which, in the wild-type strain, exerts a strict positive control on the nar operon. Both other known controls, nitrate induction and autoregulation, were unaffected. It is proposed that molecular oxygen controls the expression of nar via Fnr and that the nar ^d mutation affects the Fnr binding site of the narGHI control region.     

Foraging by the carabid Agonum dorsale in the field

Abstract. 1. Small arenas in the field were used for observing adult Agonum dorsale (Pont.) foraging in a wheat crop.
2. The carabid showed no significant change in behaviour between low and high aphid density arenas.
3. Individuals foraged nocturnally and spent most of their time on the ground searching for prey. They climbed infrequently and then not high enough to reach aphid aggregations on the ears and flag leaves of wheat.
4. Gut dissection showed that more individuals had eaten aphids in the high aphid density arena than the low. Recording of aphid distribution within the arenas showed that this increase in aphid consumption could be explained by A.dorsale capturing aphids on the ground. Prey availability per unit area was in fact higher on the ground than on the wheat.
5. The contribution of ground-zone predators such as A.dorsale to the control of cereal aphids will be determined by the frequency with which aphids arrive on the ground and the proportion of these which reclimb the wheat and reproduce in the absence of predation.     

Denture contamination by yeasts in the elderly

Objectives: The aim of this study was to investigate yeast carriage in healthy denture wearers by swabbing and to evaluate the effect of denture hygiene habits. Materials and methods: Denture wearers (n = 87) without evidence of denture stomatitis or any other oral disease were investigated by separately swabbing the fitting surface of the upper denture and the corresponding palatal mucosa in contact with the appliance. In a group of volunteers, a gel without any active compound was spread on the palatal side of the denture once in every morning for 2 weeks. Results: Screening showed Candida colonisation of upper prosthesis in 75.9% of individuals. The most frequent species isolated were Candida albicans (77.9% of the positive cultures), Candida glabrata (44.1%) and Candida tropicalis (19.1%). Carriage of more than one yeast species was found in 48.5% of the contaminated dentures. There was a statistically significant association between denture contamination and palatal mucosa colonisation (chi‐squared test: p < 0.0001). Repeated swabbings after 1 week as well as during a weekly follow‐up for 1 month confirmed the denture contamination and its degree of severity. A daily gel application produced a yeast‐count decrease to 10% of the initial value after 2 weeks (chi‐squared test: p = 0.0134 and p = 0.2841 for prosthesis and palatal mucosa, respectively). Conclusion: This study documented the reliability of oral swabbing when investigating yeast carriage in healthy denture wearers. Moreover, just a diagnostic tool, sampling upper dentures for Candida could be the opportunity to verify the patient’s compliance to hygiene advice.     

Chitin production by arthropods in the hydrosphere

Chitin is widely distributed in nature and its annual production is thought to be huge. However, the chitin production has been rarely estimated in aquatic ecosystems, despite the growing economic interest in this polymer. Arthropods are one of the main chitin producers in the hydrosphere and a correct evaluation of the chitin production by these organisms in the different marine and freshwater ecosystems is of prime interest to understand their importance in the biogeochemical cycles of carbon and nitrogen. Such evaluation is also worth considering to achieve a rational exploitation of crustaceans which are currently the major source of chitin for the industry. Annual chitin production of crustaceans and insects in aquatic ecosystems was estimated on the basis of annual tissue production estimates and body chitin content measurements. About 800 annual tissue production estimates were collected from the literature. Estimates mainly concerned continental fresh waters and neritic ecosystems. Data were almost inexistent for athalassohaline and oceanic ecosystems. On the whole, 60% of the production estimates fell between 0.1 and 10.0 g dry weight m^–2 yr^–1. Published chitin levels in crustaceans and insects ranged from 3 to 16% of the whole body dry weight. Data were, however, lacking for some major groups such as trichopterans or amphipods. Aquatic insects and crustaceans were therefore collected and assayed for chitin using a highly specific enzymatic method. The chitin content of the collected insects (Coleoptera, Diptera, Ephemeroptera, Odonata, Plecoptera, Trichoptera) varied from 3 to 10% of the whole body dry weight; that of the collected crustaceans (Amphipoda, Branchiopoda, Copepoda) from 2.5 to 8.5% of the whole body dry weight. Total annual chitin production by arthropods had been estimated to 28 × 10⁶ T chitin yr^–1 for the freshwater ecosystems, to 6 × 10⁶ T chitin yr^–1 for athalassohaline ecosystems and to 1328 × 10⁶ T chitin yr^–1 for marine ecosystems. The importance of the chitin production corresponding to the formation of exuviae and peritrophic membranes in arthropods and the chitin production by non-arthropod organisms in the chitin budget of aquatic ecosystems was highlighted and discussed.     

Presynaptic Modulation by Somatostatin in the Neostriatum

Medium spiny projection neurons (MSNs) are the main neuronal population in the neostriatum. MSNs are inhibitory and GABAergic. MSNs connect with other MSNs via local axon collaterals that produce lateral inhibition, which is thought to select cell assemblies for motor action. MSNs also receive inhibitory inputs from GABAergic local interneurons. This work shows, through the use of the paired pulse protocol, that somatostatin (SST) acts presynaptically to regulate GABA release from the terminals interconnecting MSNs. This SST action is reversible and not mediated through the release of dopamine. It is blocked by the SST receptor (SSTR) antagonist ciclosomatostatin (cicloSST). In contrast, SST does not regulate inhibition coming from interneurons. Because, SST is released by a class of local interneuron, it is concluded that this neuron helps to regulate the selection of motor acts. Special issue article in honor of Dr. Ricardo Tapia.     

Enduring Behavioral Effects Induced by Birth by Caesarean Section in the Mouse

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Fertilization by sperm injection in the rabbit

Whole rabbit spermatozoa and isolated sperm nuclei were microinjected directly into the ooplasm of hamster and rabbit ova. These injected sperm decondensed and formed male pronuclei during subsequent in-vitro culture. Injection of whole spermatozoa and sperm nuclei prepared by a protocol known to allow in-vitro capacitation of ejaculated spermatozoa yielded a significantly higher (P < 0.01) number of activated rabbit ova containing male pronuclei than did injection of uncapacitated epididymal sperm nuclei or ejaculated sperm nuclei. Rabbit ova fertilized by sperm injection were capable of undergoing normal-appearing cleavage division during 22 h of culture.     

Methylation of nuclear proteins by dimethylnitrosamine and by methionine in the rat in vivo

1. The incorporation of methyl groups into histones from dimethylnitrosamine and from methionine was studied by injection of the labelled compounds, isolation of rat liver and kidney histones, and analysis of hydrolysates by column chromatography. 2. Labelled methionine gave rise to labelled in-N-methyl-lysine, di-in-N-methyl-lysine and an amino acid presumed to be omega-N-methyl-arginine. 3. Administration of labelled dimethylnitrosamine gave rise to labelled S-methylcysteine, 1-methylhistidine, 3-methylhistidine and in-N-methyl-lysine derived from the alkylating metabolite of dimethylnitrosamine. In addition, labelled formaldehyde released by metabolism of dimethylnitrosamine leads to the formation of labelled S-adenosylmethionine, and hence to labelling of in-N-methyl-lysine, di-in-N-methyl-lysine and omega-N-methylarginine by enzymic methylation. 4. The formation of in-N-methyl-lysine by alkylation of liver histones was confirmed by using doubly labelled dimethylnitrosamine to discriminate between direct chemical alkylation and enzymic methylation via S-adenosylmethionine. These experiments also suggested the possibility that methionine residues in the histones were alkylated to give methylmethionine sulphonium residues. 5. The extent of alkylation of liver histones was maximal at about 5h after dosing and declined between 5 and 24h. The methylated amino acids resulting from direct chemical alkylation were preferentially lost: this is ascribed to necrosis of the more highly alkylated cells. 6. Liver histones were about four times as alkylated as kidney histones; the extent of alkylation of liver histones was similar to that of liver total nuclear proteins. 7. Methyl methanesulphonate (120mg/kg) alkylated liver histones to a greater extent than did dimethylnitrosamine. Diethylnitrosamine also alkylated liver histones. 8. The results are discussed with regard to the possible effects of alkylation on histone function, and the possible role of histone alkylation in carcinogenesis by the three compounds.     

Modulation of calcium by the carcinogenic process in the liver induced by a choline-deficient diet

A diet devoid of choline and low in methionine (CD), without any added carcinogen, has been shown to induce 100% preneoplastic nodules and more than 50% cancer in the rat liver. Attempts to understand the mechanism by which a CD diet induces liver cell cancer revealed that like chemical carcinogens, a CD diet also appears to cause alterations in DNA, perhaps mediated by free radicals. Indeed, a CD diet induces nuclear lipid peroxidation prior to the changes in DNA. The CD diet induced DNA alterations coupled with continuing liver cell proliferation may account for the induction of initiated hepatocytes by the CD diet. To gain insight into the nature of free radicals generated by the CD diet, experiments were designed to determine whether agents that modulate free radical effects influence the CD diet induced changes in the liver. We investigated the effect of Ca2+ in the modulation of CD diet induced alterations in the liver. The results show that extra Ca2+ when added to the CD diet prevented some of the early changes due to choline deficiency, such as nuclear lipid peroxidation and DNA damage, but had little or no effect on the triglyceride accumulation in the liver. Also, the same CD diet with extra Ca2+, when used as a promoter after initiation by diethylnitrosamine, decreased the number and size of early putative preneoplastic foci and nodules.