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, 2 February 2001, Pages
Regular articleRate of intrachain contact formation in an unfolded protein: temperature and denaturant effects, , , , a Physics Department, University of Florida, PO Box 118440 Gainesville, FL 32611, USAWe have measured the effect of temperature and denaturant concentration on the rate of intrachain diffusion in an unfolded protein. After photodissociating a ligand from the heme iron of unfolded horse cytochrome c, we use transient optical absorption spectroscopy to measure the time scale of the diffusive motions that bring the heme, located at His18, into contact with its native ligand, Met80. Measuring the rate at which this 62 residue intrachain loop forms under both folding and unfolding conditions, we find a significant effect of denaturant on the chain dynamics. The diffusion of the chain accelerates as denaturant concentration decreases, with the contact formation rate approaching a value near &6&105 s&1 in the absence of denaturant. This result agrees well with an extrapolation from recent loop formation measurements in short synthetic peptides. The temperature dependence of the rate of contact formation indicates an Arrhenius activation barrier, Ea&20 kJ/mol, at high denaturant concentrations, comparable to what is expected from solvent viscosity effects alone. Although Ea increases by several kBT as denaturant concentration decreases, the overall rate of diffusion nevertheless increases. These results indicate that inter-residue energetic interactions do not control conformational diffusion in unfolded states, even under folding conditions.Keywordsprotein folding; cytochrome c; energy landscape; denatured state; kineticsAbbreviationsGdnHCl, guanidine hydrochloride; SVD, singular value decomposition; kB, Boltzmann&s constant
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No articles found.Relationship between external resistances, lung function changes and maximal exercise capacity.
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):1369-75.Relationship between external resistances, lung function changes and maximal exercise capacity.1, , .1Dept of Pneumology, University Hospital Gasthuisberg (Leuven), Belgium.AbstractIn upper airway obstruction (UAO) the relationship between the degree of obstruction, exercise limitation and lung function indices is not well established. Therefore, we investigated in nine healthy subjects (age 36+/-9 yrs) the effects of two added resistances at the mouth (R1 = added resistance with 7.8 R2 = 5.7 mm) on forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), airway resistance (Raw) and maximal breathing capacity (measured during 15 s = measured maximum breathing capacity (MBCm); calculated as FEV1x37.5 = calculated maximum breathing capacity (MBCc)) on the one hand, and maximum exercise capacity (W'max), minute ventilation (V'E) and CO2 elimination (V'CO2) on the other. We found that R1 had almost no influence on FEV1 but decreased PEF by approximately 35% and increased Raw by almost 300%; it decreased W'max by merely approximately 10% while maximal exercise ventilation (V'Emax) was only 65% of control and only reached approximately 40% MBCc and approximately 70% MBCm; yet V'E and V'CO2 were significantly reduced at high exercise levels indicating hypoventilation. With R2, FEV1 was reduced by 25% and PEF by 55%, and Raw was increased by 600%; W'max was approximately 60% of control, V'Emax was only 35% of control and reached approximately 30% MBCc and approximately 60% MBCm, V'E was already reduced at moderate exercise levels. We conclude that: 1) an upper airway obstruction of 6 mm diameter (but not of 8 mm) had a marked influence on maximum exercise capacity du 2) calculated maximum breathing capacity markedly overestimated measured maximum breathing capacity because the forced expiratory volume in one second is an insensitive index of upper airway obstruction and because it does not take inspiratory flow lim and 3) a 10% decrease in maximum exercise capacity was linearly related with a 7% decrease in the forced expiratory volume in one second and a 150% increase in airway resistance. A 10% decrease in maximal exercise ventilation was related to a 8.5% decrease in peak expiratory flow and 9% decrease in measured maximum breathing capacity.PMID:
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