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801.
Aqueous extraction of the red alga C. rubrum gave a galactan sulphate and, possibly, a separate glucan and xylan. The galactan sulphate has an alternating structure of the agar-type with D-galactose or 6-O-methyl-D-galactose as one alternating unit, and L-galactose, 3,6-anhydro-L-galactose; and their respective 2-methyl ethers as the other unit. Sulphate hemi-ester groups are present on position 6 of both D- and L-galactose residues, with smaller amounts on positions 2 and 4 of, probably, D-galactose residues. The polysaccharide differs from others previously examined in that most of the L-galactose residues are non-sulphated. 相似文献
802.
803.
The circular dichroic spectra of the acid and sodium salt forms of several sialic acid-containing homo- and hetero-polysaccharides have been measured. The spectra are shown to be influenced by the state of ionization of the carboxyl groups contained in the sialic acid, the location within the individual sialic acid residues of the inter-saccharide linkages, and changes in the configuration of hydroxyl groups remote to the carboxyl group of the sialic acid. 相似文献
804.
G F Goubran H Cullens A J Zuckerman A L Feddleston R Williams 《BMJ (Clinical research ed.)》1976,2(6035):559-560
Sixty-one dental surgeons at King''s College Hospital were interviewed to establish the incidence of attacks of viral hepatitis and to relate this to environmental risk factors. Six (10%) had a history of hepatitis, in one case due to infection with the hepatitis B virus. Screening blood for HBsAg by radioimmunoassay showed no carriers of the antigen, but transient antigenaemia was observed in one dentist. Antibody to HBsAg, tested by radioimmunoassay, was detected in four dentists (7%), only one of whom had had clinical hepatitis. Dental surgeons may be more at risk from infection with the hepatitis B virus than the general population, although this should be minimised in hospital practice, where the most infected patients will already have been identified and appropriate precautions can be taken. The risk of transmission from an antigen-positive dentist to his patients is probably much smaller, and there is no evidence to restrict his clinical activities. 相似文献
805.
Small discrete spikes appearing on the electrocardiogram (ECG) of a man with a pacemaker turned out to be fasciculation potentials picked up from leg muscles. To find out how common these spikes were all routine ECGs made in one month were reviewed. Spike potentials were found in six patients, and in each case they originated from somatic musculature. Spikes could nearly always be detected on ECGs that were recorded subsequently in patients known to have lower motor neurone lesions that produced fasciculation. Thus the presence of these fasciculation spikes may suggest underlying neuromuscular disease; this possibility should be recognised by those who record ECGs so that the spikes are not suppressed by overuse of the filter. 相似文献
806.
Brian A. Laishes Gary M. Williams 《In vitro cellular & developmental biology. Plant》1976,12(7):521-532
Summary The conditions for obtaining representative, primary adult rat hepatocyte cultures were explored. The methods applied included
enzymatic liver perfusion which was nondestructive to hepatocytes, the prevention of aggregation of dissociated cells and
the selective attachment of viable cells. These procedures yielded a recovery of 50% of the liver cells which gave rise to
cultures representing 14% of the total liver cells. The cultures were composed of homogeneous epithelial-like cells cytologically
similar to hepatocytes and possessed a number of liver-specific enzymes. There was virtually no cell division initially and
most cells died between 24 and 48 hr. Insulin enhanced the attachment of the liver cells, altered their morphology, but did
not prolong cell survival.
This study was supported by grant no. BC 133 from the American Cancer Society. 相似文献
807.
F M Matschinsky A S Pagliara B A Hover C S Pace J A Ferrendelli A Williams 《The Journal of biological chemistry》1976,251(19):6053-6061
The glucose responsiveness of alpha- and beta-cells of normal as well as untreated and insulin-treated streptozotocin diabetic rats was tested in the extracorporeal perfusion system. Also assessed was the possible in vitro effect of added insulin on the glucose sensitivity of islets from untreated diabetic animals. Insulin and glucose responsiveness of the two cell types. The rate of glucose entry islet tissue was estimated, and the effect of glucose on the tissue supply of ATP and lactate and the cyclic 3':5'-AMP level of islets was measured under the above in vitro conditions. It was demonstrated that beta-cells are more accessible to glucose than alpha-cells, that glucose entry into islet cells is not significantly modified by insulin and that glucose had no effect on ATP, lactate and cyclic 3':5'-AMP levels of islet tissue under any of the conditions investigated. High insulin in vitro elevated ATP levels of alpha-cell islets independent of extracellular glucose. Glucose caused insulin release from normal but not from diabetic islets and rapidly and efficiently suppressed stimulated glucagon secretion of the pancreas from normal and insulin treated diabetic rats. Glucose was less effective in inhibiting stimulated glucagon secretion by the pancreas from untreated diabetic rats whether insulin was added to the perfusion media or not. Therefore, profound differences of glucose responsiveness of alpha-cells fail to manifest themselves in alterations of basic parameters of glucose and energy metabolism in contrast to what had been postulated in the literature. It is however, apparent that the glucose responsiveness of alpha-cells is modified by insuling by an as yet undefined mechanism. 相似文献
808.
Reduction of the active center disulfide bond in the flavoprotein pig heart lipoamide dehydrogenase generates two sulfur moieties which are chemically inequivalent in the 2-electron reduced form of the enzyme. Thus 1 cysteine residue is at least 13-fold more reactive than its partner toward iodoacetamide at pH 7.6. This selectivity was demonstrated by reaction of the 2-electron reduced enzyme with a low concentration of iodo[1-14C]acetamide under anaerobic conditions. The formation of a monolabeled derivative is accompanied by the reappearance of a spectrum of oxidized bound flavin, clearly different from that of the native enzyme. Alkylation of the remaining cysteine residues with iodo[12C]acetamide enabled the isolation of a tryptic version of the active center disulfide peptide. A single chymotryptic cleavage between the 2 alkylated cysteine residues generated a cationic and an anionic fragment containing 7% and 93% of the radioactivity of the purified tryptic peptide, respectively. The monolabeled derivative is catalytically inactive toward reduced or oxidized lipoamide, but is approximately 2-fold better as a transhydrogenase than the native protein using NADH and acetylpyridine adenine dinucleotide as substrates. Anaerobic titration with NADH leads to reduction of the flavin with concomitant formation of long wavelength absorption of low intensity. No intermediate reduced states were detected in this titration analogous to the red 2-electron form observed with the native enzyme. Similarly, intermediates during reduction of the enzyme by 1 eq of dithionite have not been detected. 相似文献
809.
The difference equation f
b
:[0,1]–[0,1] defined by f
b
(x)=b x(1–x) is studied. In particular complete qualitative information is obtained for the parameter value b=3.83. For example the number of fixed points of (f
b
)i is given by
Ni = 1 + ( \frac1 + ?5 2 )i + ( \frac1 - ?5 2 )iN_i = 1 + \left( {\frac{{1 + \sqrt 5 }}{2}} \right)^i + \left( {\frac{{1 - \sqrt 5 }}{2}} \right)^i 相似文献
810.
B. S. Chertow G. A. Williams Georgiann R. Baker R. D. Surbaugh G. K. Hargis 《Experimental cell research》1975,93(2):388-394
To determine the role of subcellular organelles in hormone secretion, we studied the interaction of low calcium concentration (low Ca), retinol (vitamin A, vit A), vinblastine (VB), and cytochalasin B (CB) in parathyroid hormone (PTH) secretion. Bovine parathyroid tissue pieces were incubated in media containing the above agents. Vit A stimulated PTH release to a mean of 170% of control. This effect of vit A was diminished when tissues were simultaneously stimulated with low Ca and, furthermore, absent when tissues were pre-incubated in low Ca.VB had no effect on low Ca-stimulated secretion, but did inhibit vit A-induced secretion in the presence of low Ca.CB stimulated PTH secretion to a mean of 150% of control during the second and third hours of incubation. CB had at least an additive effect with low Ca in stimulating PTH secretion, with a more prompt and greater response than seen in normal calcium. VB did not inhibit the acute effect of CB on secretion in normal calcium media, but did inhibit CB-induced secretion during the third hour of incubation.None of the agents stimulated the release of lysosomal cathepsin D, and vit A and CB did not stimulate the release of LDH.Our results suggest that; (1) vit A and low Ca stimulate PTH secretion through a common pathway involving the cell membrane; (2) CB stimulates PTH secretion through a separate effect on the cell membrane or submembrane microfilaments, which normally retards secretion of PTH; and (3) microtubular proteins may facilitate basal secretion of PTH, but are not involved in low Ca-stimulated secretion of PTH. 相似文献
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