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Biomedical subjects

Y Marcus

Publications and source records attributed to Y Marcus.

13 recordsLinked to original sources
PubMed2007

Solvent release upon ion association from entropy data. II.

When a cation and an anion associate, the charge on the product is lower than that on the individual ions and solvent is released from their solvation shells to the bulk solvent. This release occurs when the associate is a solvent-shared or contact ion pair or an inner-type complex. The measurable molar entropy change involved is considered to be made up of four contributions: translational, rotational, electrostatic, and desolvation entropies. The former three can be calculated from the properties of the ions and solvents involved; hence, the fourth is obtained by difference. The release of solvent molecules from the crystalline frozen solvent to the liquid on melting is analogous to the solvent release from translational immobilization in the solvation shells of the ions. The molar entropy of melting of the solvent is used to estimate the amount of solvent released in the association process.

Journal Article↗
PubMed2000

Infrared spectra and hydrogen bonding of pentitols and pyranosides at 20 to 300 K.

Infrared spectra in the range 400-4000 cm(-1) of three pentitols--ribitol, xylitol, D-arabinitol, and of three pyranosides--methyl alpha-D-manno-, methyl alpha-D-gluco- and methyl beta-D-galactopyranoside, as polycrystalline solids of both the pure OH and > 90% isotopically substituted OD compounds, were recorded at 20-300 K. In the low temperature spectra of the OH substances, at least three isolated narrow bands in the stretching mode and about ten narrow bands in the out-of-plane-bending mode range (< 1000 cm(-1)) are affected by cooling. Almost all have counterparts in the respective OD spectra with frequency ratios of 1.30-1.40. On this basis, they are assigned to OH groups bonded in H-bonds of different strengths (from 10 to 50 kJ mol(-1)). The average number of the OH...O hydrogen bonds is found to be two to three times larger than indicated by the stretching mode only or by structural data. The newly measured peak frequencies of the very narrow decoupled stretching mode bands show a correlation between the red shift (delta nu) and the H-bond length. As previously found for tetritols, the presence of weak H-bonds (bond energy < 14 kJ mol(-1)) is related to the different water sorption capabilities of the pentitols.

Crystallization↗
PubMed2000

Activation of cyanobacterial RuBP-carboxylase/oxygenase is facilitated by inorganic phosphate via two independent mechanisms.

Orthophosphate (Pi) modulates the activity and activation of ribulose 1,5-bis-phosphate carboxylase/oxygenase (RuBisCO) via a mechanism that is still controversial. Whereas its effects on the higher plant enzyme have been described, little is known about Pi regulation of the structurally similar, yet kinetically different cyanobacterial enzyme. We found that RuBisCO of Synechocystis PCC6803 was affected by Pi in a paradoxical fashion. On the one hand, Pi inhibited catalysis by competing with the substrate RuBP, and on the other hand it stimulated enzyme activation in a dual manner manifested by multiphasic kinetics, which differed from the effect on activation of the higher plant enzyme. Pi concentrations > 5 mM promoted the carbamylation of the cyanobacterial enzyme and the binding of Mg2+ to the carbanion at suboptimal concentrations of CO2 and Mg2+. Surprisingly, Pi also increased the activation level of the carbamylated enzyme via another putative site of interaction. In contrast with the higher plant RuBisCO, RuBP did not inhibit the stimulatory effect of phosphate on activation of the cyanobacterial enzyme, suggesting a Pi effect through a site other than the sugar binding site. The dual effect on activation could be distinguished by the phosphate analogue vanadate, which inhibited only the stimulation achieved at high phosphate concentrations. The elevation of RuBisCO activation at suboptimal levels of CO2 and high concentrations of RuBP suggests that in cyanobacteria Pi may have a role analogous to that of RuBisCO activase in higher plants.

Binding Sites↗
PubMed1989

Role of hydrophobicity in protein structure is overestimated.

Some microcalorimetrically measured and theoretically calculated thermodynamic interaction coefficients of amino acid compounds in aqueous and peptidic systems have been collected, and are reported here. They indicate that although hydrophobicity contributes to the stability of the native structure of proteins, its influence on their exact configuration is limited.

Protein Conformation↗
PubMed1989

Immediate effect of various treatments on lung function in infants with cystic fibrosis.

The immediate effect of four different modes of treatment was assessed by lung function tests on 19 infants with cystic fibrosis (CF) during the first year of life. The regimens were applied in a randomized fashion and consisted of aerosol inhalation of salbutamol (n = 8; SAL), aerosol inhalation of N-acetyl cysteine (n = 5; AC), chest physiotherapy (n = 6; CPT), and combined treatment with aerosol inhalation of SAL and AC followed by CPT (n = 6; COMB). Pulmonary function was measured before and shortly after therapy with each mode of treatment. Thoracic gas volume (Vtg) and specific airway conductance (SGaw) were measured by an infant whole body plethysmograph, and forced expiratory flow at resting lung volume (VmaxFRC) was determined with a thoraco-abdominal squeeze jacket. There was no correlation between baseline lung function and changes in any parameter due to treatment. Overall group comparison showed that the combined therapy resulted in a significant improvement in lung function when compared to any of the three treatments applied separately. There was no significant change in lung volumes in any individual group, but SGaw and VmaxFRC showed a small but significant improvement following the COMB treatment when compared with AC or CPT.

Acetylcysteine↗
PubMed1987

Adaptation to Low CO(2) Level in a Mutant of Anacystis nidulans R(2) which Requires High CO(2) for Growth.

The mutant E(1) of Anacystis nidulans R(2) requires high CO(2) concentration for growth but was able to adapt to low CO(2) concentration. This was exhibited by the increased ability to accumulate inorganic carbon within the cells and the large increase in the amount of a 42-kilodalton polypeptide located in the cytoplasmic membrane. The adaptation occurred in E(1) cells at an extracellular CO(2) concentration as high as 0.3%, which was 8 times the concentration for maximal adaptation in R(2) cells. The ability of E(1) cells to exhibit low CO(2) characteristics at a higher CO(2) concentration was attributed to lower intracellular CO(2) concentration.

Journal Article↗
PubMed1987

Energization and activation of inorganic carbon uptake by light in cyanobacteria.

The requirement of the inorganic carbon (C(i)) transport system for light in cyanobacteria was investigated in Anabaena variabilis by the filtering centrifugation technique and in a mutant (E(1)) isolated from Anacystis nidulans using a gas exchange system. C(i) transport capability increased with time of preillumination and decreased following darkening. Full activity could not be obtained by operating either photosystem II (PSII) or photosystem I alone. 3(3,4 Dichlorophenyl)-1,1 dimethylurea strongly inhibited C(i) uptake. Very low activity of PSII was sufficient to activate C(i) uptake. However, in the presence of dithiothreitol PSII activity was not required. We conclude that light may be required to activate as well as to energize C(i) uptake in cyanobacteria.

Journal Article↗
PubMed1986

Adaptation to CO(2) Level and Changes in the Phosphorylation of Thylakoid Proteins during the Cell Cycle of Chlamydomonas reinhardtii.

The photosynthetic performance of synchronously grown Chlamydomonas reinhardtii alternated rhythmically during the cell cycle. The activity of the "CO(2) concentrating mechanism" including the ability to accumulate CO(2) internally and the activity of carbonic anhydrase peaked after 6 to 9 hours of light and reached minimum after 6 to 9 hours of dark. Consequently, the apparent photosynthetic affinity to extracellular CO(2) alternated rhythmically. At the end of the dark period the cells behaved as if they were adapted to high CO(2) even though they were continuously aerated with air. Results from experiments in which the light or dark periods were extended bear on the interaction between the internal (cell cycle or biological clock) and the external (light) signal. The observed rhythmical alterations in photosynthetic V(max) may result from changes in PSII activity. The latter may be partly explained by the capacity for phosphorylation of thylakoid proteins, which reached maximum after 9 hours of light and decreased toward the dark period.

Journal Article↗
PubMed1986

High CO(2) Requiring Mutant of Anacystis nidulans R(2).

Some physiological characteristics of a mutant (E(1)) of Anacystis nidulans R(2), incapable of growing at air level of CO(2), are described. E(1) is capable of accumulating inorganic carbon (C(i)) internally as efficiently as the wild type (R(2)). The apparent photosynthetic affinity for C(i) in E(1), however, is some 1000 times lower than that of R(2). The kinetic parameters of ribulose 1,5-bisphosphate carboxylase/oxygenase from E(1) are similar to those observed in R(2). The mutant appears to be defective in its ability to utilize the intracellular C(i) pool for photosynthesis and depends on extracellular supply of Ci in the form of CO(2). The very high apparent photosynthetic K(m) (CO(2)) of the mutant indicate a large diffusion resistance for CO(2). Data obtained here are used to calculate the permeability coefficient for CO(2) between the bulk medium and the carboxylation site of cyanobacteria.

Journal Article↗
PubMed1985

Acute brain edema due to water loading in a young woman.

Increased intracranial pressure developed in a mentally and physically normal patient following ingestion of 30 glasses of water as a voluntary preparation for ultrasonic gynecological examination. Hyponatremia resulted and induced brain edema which provoked increased intracranial pressure. Hyponatremia was treated by intravenous infusion of hypertonic NaCl and mannitol solutions. Corticosteroids were added and continued for a week. The patient totally recovered 4 days after admission.

Acute Disease↗
PubMed1983

Adaptation of the Cyanobacterium Anabaena variabilis to Low CO(2) Concentration in Their Environment.

The rate of adaptation of high CO(2) (5% v/v CO(2) in air)-grown Anabaena to a low level of CO(2) (0.05% v/v in air) was determined as a function of O(2) concentration. Exposure of cells to low (2.6%) O(2) concentration resulted in an extended lag in the adaptation to low CO(2) concentration. The rate of adaptation following the lag was not affected by the concentration of O(2). The length of the lag period is markedly affected by the O(2)/CO(2) concentration ratio, indicating that the signal for adaptation to low CO(2) may be related to the relative rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activities, rather than to CO(2) concentration proper. This suggestion is supported by the observed accumulation of phosphoglycolate following transfer of cells from high to low CO(2) concentration.

Journal Article↗
PubMed1982

Induction of HCO(3) Transporting Capability and High Photosynthetic Affinity to Inorganic Carbon by Low Concentration of CO(2) in Anabaena variabilis.

The apparent affinity of photosynthesis for inorganic carbon in Anabaena variabilis strain M-3 increased during the course of adaptation from high to low CO(2) concentration (5% and 0.03% v/v CO(2) in air, respectively). This was attributed to an increased ability of the cells to accumulate inorganic carbon during the course of adaptation to low CO(2) conditions. The release of phycobiliproteins was used to evaluate the sensitivity of the cells to lysozyme treatment followed by osmotic shock. High CO(2)-grown cells were more sensitive to this treatment than were low CO(2) ones. The efflux of inorganic carbon from cells preloaded with radioactive bicarbonate is faster in high than it is in low CO(2)-adapted cells. It is postulated that the cell wall or membrane components undergo changes during the course of adaptation to low CO(2) conditions. This is supported by electron micrographs showing differences in the cell wall appearance between high and low CO(2)-grown cells. The increasing ability to accumulate HCO(3) (-) and the lessened sensitivity to lysozyme during adaptation to low CO(2) conditions depends on protein synthesis. The increase in affinity for inorganic carbon during the adaptation to low CO(2) conditions is severely inhibited by the presence of spectinomycin. Incubation in the light significantly lessens the time required for the adaptation to low CO(2) conditions.

Journal Article↗