Protein stability and electrostatic interactions between solvent exposed charged side chains

To investigate the contribution to protein stability of electrostatic interactions between charged surface residues, we have studied the effect of substituting three negatively charged solvent exposed residues with their side-chain amide analogs in bovine calbindin D9k--a small (Mr 8,500) globular protein of the calmodulin superfamily. The free energy of urea-induced unfolding for the wild-type and seven mutant proteins has been measured. The mutant proteins have increased stability towards unfolding relative to the wild-type. The experimental results correlate reasonably well with theoretically calculated relative free energies of unfolding and show that electrostatic interactions between charges on the surface of a protein can have significant effects on protein stability.     

The effects of cultural conditions on growth and secondary metabolism in Streptomyces thermoviolaceus

Abstract Granaticin, an isochromate quinone antibiotic is synthesized as a secondary metabolite by Streptomyces thermoviolaceus . Antibiotic productivity was investigated under a variety of cultural conditions, including complex and defined media, mesophilic and thermophilic temperatures and a variety of sole carbon sources. In a defined medium growth was supported, to varying extents, by different carbon sources and in most cases granaticin production was observed. Highest biomass and granaticin yields were obtained when cultures were grown in the presence of xylan, fructose, glutamate or proline as carbon source. Changes in pH during growth affected both the timing and extent of granaticin production.     

Karyological stability and microevolution of a cell suspension culture ofBrachycome dichromosomatica (Asteraceae)

A long-term suspension culture ofBrachycome dichromosomatica (2n = 4) was induced from a cotyledon-derived callus. Subcultures were obtained every week up to three years. The bulk of the cultures displayed a stable diploid karyotype, while one cell line evolved with 2n = 5 chromosomes in the 86th reinoculation. No further chromosomal change occurred also in that cell line. It is assumed that the fifth chromosome is the expression of a trisomy 2.The chromatin ultrastructure was of the species-specific chromomeric type in the wild-type line, while the trisomic line displayed more condensed chromatin, what probably indicates a rather inactive state of the extra-chromosome.Brachycome dichromosomatica is suggested to represent an ideal species to follow-up karyotype stability and/or variation in cell culture.As a former student W. N. dedicates this paper in gratitude and admiration to Prof. DrElisabeth Tschermak-Woess on the occasion of her 70th birthday. Prof.Woess with her scientific work has stimulated in an unique manner the study of nuclear structures in plants, of endopolyploidy and polytene chromosomes, and has thus established the basis for the rapidly increasing research in these fields.     

Ion currents associated with root tips, emerging laterals and induced wound sites in Nicotians tabacum: spatial relationship proposed between resulting electrical fields and phytophthoran zoospore infection

Abstract Growing roots of Nicotiana tabacum var. Havana generate transcellular ion currents which traverse developing and wounded tissues. Positive current of around 10 mA m^?2 enters meristematic and elongating cells at the tip of primary roots. The growing tips of first order laterals are also traversed by a similar positive current with a density of around 2.0 mA m^?2, as are immature laterals emerging at the primary root surface. These self-generated ion currents flow basipetally through developing tissues and leave from mature non-elongating tissue. A large positive current of around 70 mA m^?2 also enters induced wound sites on the primary root surface. Motile zoospores of the fungal pathogen Phytophthora parasitica var. nicotianae have been reported to associate preferentially with these regions of the root. This might suggest that electrotaxis may be part of the mechanism by which zoospores locate root regions susceptable to fungal infection.     

Electrical stability of erythrocytes in the presence of divalent cations

Erythrocytes suspended in a medium of low ionic strength lyse under the effect of an exponential electrical pulse. The percentage of haemolysed cells decreases several-fold in the presence of divalent cations. The protective action of the ions studied increases in the following order: Ca⁺⁺, Mg⁺⁺, Zn⁺⁺. It is assumed that divalent ions bind to the negative charges of the lipid and protein molecules and reduce their electrostatic repulsion, which results in stabilization of the membranes.     

Protection of photosynthetic O2 evolution against heat inactivation: the role of chloride,pH and coupling status

Heat inactivation of photosynthetic O₂ evolution was studied in isolated thylakoids from spinach (Spinacia oleracea) and mangrove (Avicennia marina) leaves. Different temperatures, salt, pH and uncoupler effects were investigated. From these results and others in the literature it was concluced that chloride loss from the membrane and, more specifically, the oxygen-evolving complex of photosystem II, may be the cause of inhibition of oxygen evolution during heat inactivation.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazinethanesulfonic acid - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol - Tricine N-2-hydroxy-1, 1-bis (hydroxymethyl) ethyl glycine - EDTA ethylenediaminetetraacetic acid - FeCN K-ferricyanide     

The effects of guanine and cytosine variation on dinucleotide frequency and amino acid composition in the human genome

Summary One hundred twelve human DNA sequences were analyzed with respect to dinucleotide frequency and amino acid composition. The variation in guanine and cytosine (G+C) content revealed: (1) at 2–3 and 3-1 doublet positions CG discrimination is attenuated at high G+C, but TA disfavor is enhanced, and (2) several amino acids are subject to G+C change. These findings have been reported in part for collections of sequences from various species. The present study confirms that in a single organism-the human-the G+C effects do exist. Aspects of the argument that connects G+C with protein thermal stability are also discussed.     

Brain Metabolism and Intracellular pH During Ischaemia: Effects of Systemic Glucose and Bicarbonate Administration Studied by 31P and 1H Nuclear Magnetic Resonance Spectroscopy In Vivo in the Lamb

Brain metabolism and intracellular pH were studied during and after episodes of incomplete cerebral ischaemia in lambs under sodium pentobarbitone anaesthesia. 31P and 1H magnetic resonance spectroscopy was used to monitor brain pHi and brain concentrations of inorganic phosphate (Pi), phosphocreatine (PCr), beta-nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of arterio-cerebral venous concentration differences (AVDs) for oxygen, glucose, and lactate. Cerebral ischaemia was induced by a combination of bilateral carotid clamping and hypotension, and the acute effects of systemic administration of glucose and sodium bicarbonate were examined. The molar ratio of glucose to oxygen uptake by the brain (6G/O2) increased above unity during cerebral ischaemia. Statistically significant AVDs for lactate were not observed. Cerebral ischaemia was associated with a reduction in brain pHi PCr/Pi ratio, and an increase in brain lactate. No effect of arterial plasma glucose on brain lactate concentration or brain pHi was evident during cerebral ischaemia or in the postischaemic period. Administration of sodium bicarbonate systemically in the postischaemic period was associated with a rise in arterial and brain tissue PCO2. A fall in brain pHi occurred which was attributable in part to coincidental brain lactate accumulation. The increase in brain lactate measured by 1H nuclear magnetic resonance in vivo during ischaemia was insufficient to account for the change in buffer base calculated to have occurred from previous estimates of brain buffering capacity.     

pH Dependence of Histidine Affinity for Blood-Brain Barrier Carrier Transport Systems for Neutral and Cationic Amino Acids

The effects of pH (3.5-7.5) on the brain uptake of histidine by the blood-brain barrier (BBB) carriers for neutral and cationic amino acids were tested, in competition with unlabeled histidine, arginine, or phenylalanine, with the single-pass carotid injection technique. Cationic amino acid ( [14C]arginine) uptake was increasingly inhibited by unlabeled histidine as the pH of the injection solution decreased. In contrast, the inhibitory effect of unlabeled histidine on neutral amino acid ( [14C]phenylalanine) uptake decreased with decreasing pH. Brain uptake indices with varying histidine concentrations indicated that the neutral form of histidine inhibited phenylalanine uptake whereas the cationic form competed with arginine uptake. Since phenylalanine decreased [14C]histidine uptake at all pH values whereas arginine did not, it was concluded that the cationic form of histidine had an affinity for the cationic carrier, but was not transported by it. We propose that the saturable entry of histidine into brain is, under normal physiological circumstances, mediated solely by the carrier for neutral amino acids.