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111.
A method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. The method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. The significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with good accuracy and precision. A series of results from normal myelinated nerve fibers from Xenopus laevis is presented. Considerable variation (up to 50%) in mean velocity was found between individual nerve fibers. The mean of all determinations indicates that the mean velocity of somatopetally moving particles in axons with diameters greater than 10mum is in the region of 1.14 mum/s at a temperature of 22-24 degrees C. The findings are compared with small collection of such determinations which have been reported in the literature. 相似文献
112.
113.
Prolactin binding activity was studied in suspensions of cells which had been enzymatically dissociated from R3230AC mammary tumors, 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors and lactating rat mammary glands. Prolactin bound specifically with high affinity (apparent binding affinity = 4.0 X 10(9) M-1) to R3230AC tumor cells. Hormone binding at room temperature was proportional to cell number and increased with time of incubation up to 120-180 min. Prolactin binding to R3230AC tumor cells from diabetic animals was reduced by about 50%. Specific prolactin binding activity was also demonstrated in preparations of cells from DMBA-induced tumors and lactating mammary gland. The levels of hormone binding in both dissociated cells and subcellular particles prepared from these tissues varied as follows: DMBA-induced tumors > lactating mammary gland > R3230AC mammary adenocarcinoma. 相似文献
114.
L S Smith C W Kern R M Halpern R A Smith 《Biochemical and biophysical research communications》1976,71(2):459-465
Isolated rat brain myelin when incubated with γ32P labelled ATP yields proteins bearing acid labile, base stable phosphoryl groups. Phosphorylated myelin basic protein can be isolated and degraded with trypsin and pronase to yield principally phosphoarginine and phosphohistidine. Only a very small amount of phosphorerine survives the base treatment used in the isolation procedure. 相似文献
115.
116.
Between 1970 and 1975, 108 patients who presented with advanced or recurrent Hodgkin''s disease and were free of disease after six courses of chemotherapy with mustine, vinblastine, procarbazine, and prednisone (MVPP) were allocated at random to one of two regiments of maintenance treatment: either intermittent treatment with vinblastine and procarbazine or intermittent treatment with MVPP. After a median follow-up period of nearly five years there was no significant difference between the two groups in either the rate of relapse or death rate. Six of the 55 patients given the two-drug regimen died compared with 10 of the 53 given the four-drug regimen. The four-drug required hospital attendance and was less agreeable than the two-drug regimen. The efficacy of maintenance chemotherapy with the two-drug regimen was no less than that with the four-drug regimen, but the two-drug regimen had several practical advantages. 相似文献
117.
The number of metal atoms contained within a displaceable inorganic component of a metalloprotein was determined by considering X-ray absorption by single crystal samples of holo- and apo-proteins. Since this method is non-destructive, it can be used to determine the number of metal atoms associated with the molecules forming the crystal actually used for X-ray diffraction data collection and subsequent structure solution. The method has been applied to the iron storage protein ferritin, isolated from horse spleen, to give a reliable estimate of the average iron content of the ferritin molecules within the crystal. This value, of around 2000 iron atoms per molecule is consistent with that found for a typical ferritin preparation in solution and suggests non-selectivity of the crystallisation process for ferritin in terms of molecular iron content. 相似文献
118.
A T Smith S A Sanders R N Thorneley J F Burke R R Bray 《European journal of biochemistry》1992,207(2):507-519
A horseradish peroxidase variant ([F41V] HRP-C*), in which Val replaces the conserved Phe at position 41 adjacent to the distal His, has been constructed. Its composition and spectroscopic, catalytic and substrate-binding properties were compared with those of the wild-type recombinant (HRP-C*) and plant (HRP-C) enzymes. Presteady-state kinetic measurements of the rate constant for compound I formation (k1) revealed an eightfold decrease in the reactivity of the Phe41----Val variant towards H2O2, in comparison with HRP-C or HRP-C*. Measurement of the remaining rate constants, k2 and k3, for the two single-electron reduction reactions of [F41V] HRP-C with para-aminobenzoic acid as reducing substrate, showed that they were 2.5-fold and 1.3-fold faster, respectively. In contrast, analysis of data from steady-state assays with 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonate) as reducing substrate, showed decreased reactivity of the mutant enzyme to this compound, indicating a change in substrate specificity. Over the substrate range studied, the data for HRP-C* and for [F41V] HRP-C conformed to a simple modification of the accepted peroxidase mechanism in which a first-order step (ku), assumed to be product dissociation, becomes rate-limiting under our standard assay conditions. Calculations of rate constants from steady-state data yielded values of k1 for both enzyme forms in adequate agreement with those from pre-steady state measurements. They showed, furthermore, that both k3 for 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonate) and ku were substantially decreased, fivefold and tenfold, respectively, in the mutant. Analogous to the decrease in ku, we observed a twofold increase in the affinity of the mutant variant for the inhibitor benzhydroxamic acid. The coordination-state equilibrium of the haem iron also appeared shifted towards the hexacoordinate high-spin form. These observations indicate that in addition to affecting reactivity to H2O2, mutations in the distal region and close to the haem iron also affect reactivity towards different reducing substrates, inducing perturbations in the neighbourhood of the aromatic-substrate-binding site, known to be 0.8-1.2 nm from the haem iron. 相似文献
119.
T K Smith A Crossman C N Borissow M J Paterson A Dix J S Brimacombe M A Ferguson 《The EMBO journal》2001,20(13):3322-3332
The substrate specificities of Trypanosoma brucei and human (HeLa) GlcNAc-PI de-N-acetylases were determined using 24 substrate analogues. The results show the following. (i) The de-N-acetylases show little specificity for the lipid moiety of GlcNAc-PI. (ii) The 3'-OH group of the GlcNAc residue is essential for substrate recognition whereas the 6'-OH group is dispensable and the 4'-OH, while not required for recognition, cannot be epimerized or substituted. (iii) The parasite enzyme can act on analogues containing betaGlcNAc or aromatic N-acyl groups, whereas the human enzyme cannot. (iv) Three GlcNR-PI analogues are de-N-acetylase inhibitors, one of which is a suicide inhibitor. (v) The suicide inhibitor most likely forms a carbamate or thiocarbamate ester to an active site hydroxy-amino acid or Cys or residue such that inhibition is reversed by certain nucleophiles. These and previous results were used to design two potent (IC50 = 8 nM) parasite-specific suicide substrate inhibitors. These are potential lead compounds for the development of anti-protozoan parasite drugs. 相似文献
120.
The present study analyzed 42 organic solvent extracts of scent mark pools from five dominant female common marmosets by gas chromatography (GC) and combined GC and mass spectrometry. We determined whether there were qualitative or quantitative differences between the chemical composition of scent marks from individual females. Gas chromatography and mass spectral analysis detected the same 162 chemicals in 86% (36/42) of scent mark pools from five dominant females. This near identical chemical composition of scent marks suggested there were few, if any, qualitative differences between the chemical composition of scent marks from individual females. Instead, quantitative differences in scent may provide the key factor distinguishing individual females. Using the relative concentration of highly volatile chemicals detected by GC in scent marks, linear discriminant analysis classified scent mark pools to their correct donor approximately 91% of the time. Such highly reliable statistical matching of scent to donor suggested that each individual female common marmoset has a unique ratio of highly volatile chemicals in their scent marks which may permit individual identification of females from odors in their scent alone. 相似文献