Showing papers in "Biochemical Society Transactions in 1983"

Determinations of total carotenoids and chlorophylls a and b of leaf extracts in different solvents

Abstract: Various equations for the determinations of total chlorophyll and individual amounts of chlorophylls a and b in extracts from plant tissues exist (see Holden, 1976) and some of them (e.g. Arnon, 1949) are widely used. Additional modifications to the equations have also been developed so as to permit an estimate of total carotenoids to be made from the spectrum of the same mixture in diethyl ether (Ziegler & Egle, 1965; Gaudillire, 1974). During the course of studies that involved the use of various solvents we noted large discrepancies (>40%) between estimations made using the different published equations for particular solvents, all of which were known to contain the same amount of pigments. Taking advantage of a t.1.c. method (Lichtenthaler 8t Pfister, 1978) that permits a distinct separation of the two chlorophylls and also the major carotenoids using light petroleum (b.p. 40-6O0C)/dioxane/propan-2-ol (7 :3 : 1, by vol.) as developing solvent, fresh samples of chlorophyll a and b uncontaminated with each other were readily available for re-evaluation of the published specific absorption coefficients. Those values published by Smith & Benitez (1955), using diethyl ether, were found to be still the most acceptable, and relative specific absorption coefficients to these values were established (Table 1) for various other solvents. The red peak maxima of the chlorophylls were shifted to longer wavelengths with increasing polarity of the solvents; in our case diethyl ether, acetone, 80% (v/v) acetone, 96% (v/v) ethanol and methanol. The red absorption peaks of the chlorophylls were also broadened in the same sequence and the values for the specific absorption coefficients decreased. At the same time suitable values for total carotenoids at 470nm were also determined. On the basis of these coefficients the following equations were derived to determine the individual levels of both chlorophyll a (C,) and chlorophyll b (C,) and the total amounts of carotenoids (Cx+c) and chlorophylls (C,+ C,) [in pg.(ml of plant extract)-'] the measured absorbance values (A) at different wavelengths:

Preparation and Analysis of Protein Crystals

Abstract: The best ebooks about Preparation And Analysis Of Protein Crystals that you can get for free here by download this Preparation And Analysis Of Protein Crystals and save to your desktop. This ebooks is under topic such as preparation and analysis of protein crystals preparation and analysis of protein crystals amazon s3 preparation of protein crystals for x-ray structural study preparation analysis of large, flat crystals ca2 how to grow single crystals for x-ray analysis by solution monitoring preparation of derivative protein crystals via preparation and analysis of protein crystals by a chapter 1 preparation of 2d crystals of membrane maldi sample preparation south dakota state university introduction to protein crystallization kemisk institut facilities and methods for the high-throughput crystal preparation and analysis of large, flat crystals of ca(2 new crystal form of cytosolic chicken aspartate two-dimensional crystals of rhodopsin 91 sample preparation and mass-spectrometric characterization x-ray analysis of protein crystals with thin-plate morphology protein preparation, crystallization and preliminary x-ray of chemistry vol 261, no march 25, pp by of inc usa x-ray crystallography methods 2005 colgate university preliminary characterization of crystals of the protein protein x-ray crystallography methods influence of matrix solution conditions on the maldi-ms three-layer matrix/sample preparation method for maldi ms sample preparation for crystallization urine sediment guide idexx laboratories diagnÃÂ3stico protein preparation, crystallization and preliminary x-ray protein preparation, crystallization and preliminary x-ray crystal growth purià ̄¥cation, refolding, crystallization and supplementary materials and methods protein preparation a general protocol for the crystallization of membrane solubility & stability screen huji growth and characterization of lysozyme crystals in a general method for hyperquenching protein crystals statistical analysis of crystallization database links mass spectrometric analysis of mercury incorporation into characterization of the growth of 2d protein crystals on a protein spherulites for sustained release of interferon how to prepare ir samples? preparation of large-volume crystals for structure the impact of protein characterization in structural a high-pressure cryocooling method for protein crystals atomic-resolution structures from fragmented protein mass spectrometry of whole proteins eluted from sodium structural proteomics: prospects for high throughput chemistry 51 experiment 11 synthesis and analysis of aspirin

Proteoglycans as organizers of the intercellular matrix.

Abstract: Introduction The evolution of multicellular organisms made necessary the development of an extracellular matrix to protect cells and to bind them together in a spatial arrangement required for specialized anatomical and physiological functions. Thus the extent of the matrix and how it is organized in different parts of the body depend on the specialized functions of cells. The matrix in its turn influences the sorting and organization of cells during embryonic development of animals (see Hay, 198 1). Collagen is the principal structural protein of animals, a primitive form of which was evolved by Porifera (Mathews, 1967; Adams, 1978). It has proved so suitable that it is highly conserved and remains the prime structural protein of higher animals, providing the fibrous framework for the body. The extracellular matrix also contains polyanionic macromolecules which fill the interfibrillar space and complement the role of collagen by retaining water in the tissue and controlling its flow (see below). In Nature, polyanions predominate in the pericellular environment, and it has been suggested (Scott, 1975, 1979) that this predominance arose because the Donnan effects of polyanions would exclude from their domains the extremely reactive hydrated electrons produced by ionizing radiations on water. Pericellular polyanions would thus have protected primitive organisms from damage by hydrated electrons and their reactive products generated by the intense radiation that reached the biosphere when there was a thinner protective ozone layer because there was less oxygen in the atmosphere. The acidic polysaccharides of the extracellular matrix of vertebrates are much less diverse than those of invertebrates (Mathews, 1967). In mammals there are a limited number, based on differences in repeating disaccharide units of which they are composed. They are collectively known as glycosaminoglycans and are long unbranched chains with many carboxy and/or sulphate groups made up of disaccharide units of hexosamine and uronic acid or hexosamine and galactose (for reviews, see Muir & Hardingham, 1975: Hardingham, 198 1). However, with the probable exception of hyaluronic acid, all glycosaminoglycans are attached at the reducing end to specific proteins to form large macromolecules known as proteoglycans, a term introduced in 1967 (see Balazs & Gibbs, 1970). Several glycosaminoglycan chains are attached laterally to the protein, from which they extend outwards like a bottle brush owing to electrostatic repulsion of their negatively charged groups. The physical properties of different tissues of the body depend mainly on differences in the proportion of collagen to proteoglycan. which varies widely, and also on the type of proteoglycan and collagen and how these are organized in the matrix. The specific anatomical distribution of different proteoglycans and collagen implies that they have different functions, although these are not yet known precisely. The organizing functions of proteoglycans can be roughly separated into space-filling functions and specific interactions; however, much more is known about the former than the latter. The space-filling role of proteoglycans is very important in cartilage. where the concentration of proteoglycans is higher than in any other tissue. Most progress has therefore been made in elucidating structure and function of proteoglycans of cartilage, which have particular features necessary for this space-filling role, which will be discussed in detail below.

Hypothesis on the molecular basis of the antifungal activity of N-substituted imidazoles and triazoles.

Abstract: known as denmert) caused total loss of its fungicidal activity towards Sphaerotheca fuliginea and Monilinia fmctigena. These workers suggested that the co-ordination of the heterocyclic meta-nitrogen atom of buthiobate to a cationic receptor site may be important for its fungicidal activity. The cationic receptor site mentioned would appear to be the Fez+ of the cytochrome P-450 catalysing step 1 of the sterol 14-demethylation sequence.

Control of gluconeogenesis in rat liver cells

Abstract: Control of gluconeogenesis from lactate was studied by titrating rat liver cells with lactate and pyruvate in a ratio of 1 O : l in a perifusion system. At different steady states of glucose formation, the concentration of key gluconeogenic intermediates was measured and plotted against gluconeogenic flux (Jglucoee). Complete saturation was observed only in the plot relating JglUcto the extracellular pyruvate concentration. Measurement of pyruvate distribution in the cell showed that the mitochondrial pyruvate translocator operates close to equilibrium at high lactate and pyruvate concentrations. It can therefore be concluded that pyruvate carboxylase limits maximal gluconeogenic flux. Addition of glucagon did not cause a shift in the plots relating Jglueose to glucose 6-phosphate, dihydroxyacetone phosphate, 3-phosphoglycerate, and phosphoenolpyruvate. It can thus be concluded that glucagon does not affect the kinetic parameters of the enzymes involved in the conversion of phosphoenolpyruvate to glucose. Addition of glucagon led to a shift in the curves relating Jglueose to the concentration of cytosolic oxalacetate and extracellular pyruvate. The shift in the curve relating JgluCto oxalacetate is due to glucagon-induced inhibition of pyruvate kinase. The stimulation of gluconeogenesis by glucagon can be accounted for almost completely by inhibition of pyruvate kinase. There was almost no stimulation by glucagon of pyruvate carboxylation. In the absence of glucagon, control on gluconeogenesis from lactate is distributed among different steps including pyruvate carboxylase and pyruvate kinase. Assuming that in the presence of glucagon all pyruvate kinase flux is inhibited, the control of gluconeogenesis in the presence of the hormone is confined exclusively to pyruvate carboxylase.

Secondary carnitine insufficiency in disorders of organic acid metabolism: modulation of acyl-CoA/CoA ratios by l-carnitine in vivo

Abstract: RONALD A. CHALMERS,* CHARLES R. ROE,? BERYL M. TRACEY,* TERRY E. STAGEY,* CHARLES L. HOPPELS and DAVID S. MILLINGTONt * Paediatric Research Group, M.R.C. Clinical Research Centre, Watford Road, Harrow Mid&. HA1 JUJ, U.K., +Division of Pediatric Metabolism, Duke University Medical Center, Durham, NC 2 7710, U.S.A., and $ Veterans' Administration Medical Center, Departments of Pharmacology and Medicine. Case Western Reserve University School of Medicine, Cleveland, OH 44106, U.S.A.

Microbial fuel cells

Abstract: Microbial fuel cells containingProteus vulgaris and oxidation-reduction (“redox”) mediators were investigated. The bacteria were chemically immobilized onto the surface of graphite felt electrodes, which supported production of continuous electric current and could be reused after storage A computer-controlled carbohydrate feed system enabled the cell to generate a constant output with improved efficiency compared to the performance obtained with single large additions of fuel. The response to additions of substrate when immobilized bacteria were used was faster than that achieved with freely suspended organisms. This is attributed to the advantageous mass-transfer kinetics resulting from the proximity of the immobilized bacteria and the electrode surface.

The biosynthesis of iridoid glucosides from 8-epi-deoxyloganic acid

Abstract: species. Similar findings have previously been reported for M. piperita (Bricout & Paupardin, 1975) and M. rotundifolia (Bricout et al., 1978). Many of the calluses accumulate only the early precursors of the monoterpenes (namely geraniol, linalol and lavandulol), but some species give rise to cultures that accumulate monoterpenes characteristic of the intact plant. For example, cell lines from M. spicata x suaueolens accumulate carvone (the major terpene component of both the intact plant and the parent M. spicata) and sesquiterpenes. Maximum accumulation occurs in late exponential phase cells, but accumulation is appreciably higher in liquid suspension cultures than in the corresponding calluses. Supplementation of the growth medium with citric, fumaric, malic or pyruvic acids leads to a general, but small, enhancement of monoterpene accumulation. In some instances,

Applications of electron transfer between biological systems and electrodes.

Abstract: The demonstration of rapid and reversible electron transfer between cytochrome c and a gold electrode in the presence of 4,4’-bipyridyl (Eddowes & Hill, 1977; Albery et al., 1981) offered the opportunity for development of a new generation of bioelectrochemical devices. Extension of this work on ‘promoted‘ electron transfer to other redox proteins such as bacterial ferredoxin (Armstrong et al., 1982), together with successes in coupling oxidoreductases such as nitrate reductase to these modified electrodes (Hill et al., 1981), provided a means of tightly linking enzyme-catalysed reactions to solid electrodes. A complementary method of achieving direct electron transfer is the use of chemical ‘mediators’, which, unlike the ‘promoters’ they replace, undergo redox reactions during translocation of electrons between proteins and electrodes (Plotkin et al., 1981; Turner et al., 1982a,b). Mediators may also be immobilized on or within the electrode surface, which when coated with an appropriate oxidoreductase provide commercially important catalytic electrodes.

How is sterol synthesis regulated in higher plants

Abstract: dione); 1 1flOH-P (1 1/?-hydroxyprogesterone; 1 1 /?-hydroxypregn-4ene-3,20-dione); 1 I-0x0-P (1 1-oxoprogesterone; pregn-4-ene-3,11,20trione); 21-d-F (2 I-deoxycortisol; 11/?,17a-dihydroxypregn-4-ene-3,20dione); 2 1 -d-E (2 1-deoxycortisone; 17a-hydroxypregn-4-ene-3,11,20trione); 1 1-deoxycortisol (Reichstein’s substance S ; cortexolone; 1 7 ~ 2 l-dihydroxypregn-4-ene-3,20-dione); DHS (dihydro substance S; dihydro-1 1-deoxycortisol; 1 7a,2 1 -dihydroxy-5/?,pregnane-3,20-dione); THS (5fltetrahydro substance S ; tetrahydro-I 1-deoxycortisol; 3/?,17a,21-trihydroxy-5/?-pregnan-20-one); DOC (1 l-deoxycorticosterone; cortexone; 2 1 -hydroxypregn-4-ene-3,2O-dione); TH-DOC (tetrahydro1 1-deoxycorticosterone; 342 l-dihydroxy-5/?-pregnan-20one); aldosterone (1 lp,2 l-dihydroxy-pregn-4-ene-3,18,2O-trione); 2a-Me,9a-FI-F (9a-fluoro-2a-methyl-1 I/?, 17a,21-trihydroxypregn-4ene-3,20-dione); glycyrrhetinic acid (glycyrrhetic acid; 3Fhydroxy1 I-oxo-olean-12-en-30-oic acid); brassinolide [2 a,3 a,(ZZR)-(23R)-tetra hydroxy-(24S)-methyl-B-homo-7-oxa-5a-cholestan-6-onel.

Biosynthesis of abscisic acid

Abstract: The fungus Cercospora rosicola has been studied as a model system for abscissic acid biosynthesis. 1'-dDeoxyabscissic acid and 4'-hydroxy-a-ionylidene acetic acid have been identified as endogenous compounds in this fungus. The results of feeding these and other putative intermediates suggest that abscissic acid biosynthesis proceeds via the successive oxidations of a 3-methyl-5-(2',6',6'-trimethylcyclohex-2'-en-1'-yl)-2,4-pentadienyl intermediate. Preliminary results suggest that a similar pathway may operate in plants.

Approaches to enzyme stabilization

Abstract: much less stable in both cases (Wiseman et al., 1975). Reduced forms contain Fe\", which is a high-spin-state form, and this may explain the lower stability, although there is a possibility of a conformational difference for the Fel* form associated with its mechanistic role in oxygen binding. This is another possible case, therefore, of a mechanistic advantage and stability being mutually exclusive. It is clear that, for a cytochrome P-450 acting on a Type I substrate, the enzyme will be more unstable in use (i.e. in the presence of substrate if no compensating stabilization occurs on its binding) than in storage, because the substrate converts the enzyme into the high-spin form. Type I1 substrates, however, have lower rates, but higher stability in use. Several Type I1 ligands, including enzyme inhibitors, should be tested as stabilizers for storage of these enzymes. Consideration of enzyme mechanism may therefore be of general interest in relation to stability. Induced fit and other likely mechanisms of increasing rates of enzyme reactions may also diminish the stability of the enzyme. Therefore, although the efficiency of the enzyme, expressed as kCat.lK,, may be higher, lowered stability may also result in some cases (especially in highly evolved enzymes) from adverse conformational or electronic changes. These factors, where opposing, must be considered in selecting enzymes-and in the future in designing them!

The role of oxysterols in the regulation of cholesterol biosynthesis.

Abstract: Most mammalian cells are able to satisfy their requirements for cholesterol from either external (lipoprotein) or internal (biosynthetic) sources. Although the rate of cellular cholesterol biosynthesis appears to bear an inverse relationship to the availability of external lipoprotein cholesterol, the exact nature of the regulatory molecule(s) remains to be unequivocally established. Several oxygenated derivatives of cholesterol (oxysterols) are powerful inhibitors of cholesterol biosynthesis, an effect which appears to be due primarily, but not exclusively, to a decrease in the activity of HMG-CoA* reductase. One of the aims of the present paper is to examine the relationship between oxysterol structure and inhibitory potency. Various hypotheses have been proposed to explain the means by which these compounds exert their effects at the molecular level and these will also be discussed. However, the main objective of this paper is to review the evidence for the natural involvement of a component of this type in the normal regulatory sequence of events culminating in the suppression of cellular cholesterol biosynthesis.

Polyprenol-linked sugars and glycoprotein synthesis in plants.

Abstract: Introduction Protein glycosylation is a universal feature of all eukaryotic organisms and has been the subject of intensive studies for several years. Lipid-linked saccharides, or lipid-intermediates, of a type similar to those involved in the biosynthesis of cell wall polysaccharides in bacteria (see, for example, Hemming, 1974) have also been shown to participate in the formation of glycoproteins. The present short review tries to summarize the current state in plant systems. Since much of the initial work has been carried out in animal and yeast, reference will be made to those studies. For a more detailed bibliography the reader is referred to recent reviews (Parodi & Leloir, 1979; Elbein, 1979; Hubbard & Ivatt, 198 1 ; Lehle, 198 la).