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۱REASSOCIATION AND REACTIVATION OF GLUCOSE 6–PHOSPHATE DEHYDROGENASE FROM STREPTOMYCES AUREOFACIENS AFTER DENATURATION BY 6 M UREA
نویسنده(ها): ،
اطلاعات انتشار: Journal of Sciences، چهاردهم،شماره۲(پياپي ۵۳)، spring ۲۰۰۳، سال
تعداد صفحات: ۱۰
Glucose 6–phosphate dehydrogenase (G6PD) from Streptomyces aureofaciens was purified and denatured in 6 M urea. Denaturation led to complete dissociation of the enzyme into its inactive monomers, 98% loss of the enzyme activity, about 30% decrease in the protein fluorescence and a 10 nm red shift in the emission maximum. Dilution of urea–denatured enzyme resulted in regaining of the enzyme activity and the native protein fluorescence. The renatured enzyme was indistinguishable from the native enzyme based on a number of enzymological and physicochemical criteria. Regaining of the protein fluorescence occurred immediately after diluting the denatured enzyme and before reactivation started. The reactivation process was also monitored by measuring the accessibility of histidine residues toward diethylpyrocarbonate modification. As the reactivation proceeded, less histidine residues were able to be modified. Nicotineamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADP+) and glucose 6–phosphate stimulated the reactivation rate at different degrees. It seemed likely that specific ligands stimulated reactivation by binding to an inactive form of the enzyme leading to a different pathway of refolding. The data are consistent with a model for enzyme renaturation and reactivation in which NAD+ and NADP+ pull the enzyme toward different conformational structures.

۲EFFECT OF TIME–DEPENDENT TRANSPIRATION ON AXISYMMETRIC STAGNATION–POINT FLOW AND HEATTRANSFER OF A VISCOUS FLUID ON A MOVING CIRCULAR CYLINDER
نویسنده(ها): ،
اطلاعات انتشار: International Journal of Engineering، بيست و سوم،شماره۳-۴، November ۲۰۱۰، سال
تعداد صفحات: ۲۶
Effect of time dependent normal transpiration ( ) 0 U t on the problem of unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite circular cylinder moving simultaneously with time–depended angular and axial velocities and with time–dependent wall temperature or wall heat flux are investigated. The impinging free stream is steady with a strain rate . A reduction of Navier–Stokes equations and energy equation is obtained by use of appropriate transformations. The general semi–similar solutions are obtained when angular and axial velocities of the cylinder and also its wall temperature or its wall heat flux vary as certain functions of time. The cylinder may perform different types of motions. It may move or rotate with constant speed, with exponentially increasing\decreasing axial\angular velocity, with harmonically varying axial\angular speed, or with accelerating\decelerating oscillatory axial\angular speed. The cylinder surface temperature or its surface heat flux may have the same type of behavior as the cylinder motion. Semi–similar solutions of the unsteady Navier–Stokes and energy equations are obtained numerically using a finite–difference scheme.All the solutions above are presented for different Reynolds numbers (Re = ka2 \ 2u ) and different functions of dimensionless transpiration rate, ( ) ( ) \( ) 0 S t = U t ka , where is cylinder radius and is kinematic viscosity of the fluid. Shear stresses corresponding to all the cases increase with the increase of Reynolds number and decrease with the increase of suction rate. The maximum value of shear stress increases with increase of oscillation frequency and amplitude. An interesting result is obtained in which a cylinder moving with certain angular\axial velocity function and at particular values of Reynolds number is azimuthally\axially stress–free. Heat transfer rate increases with the increase of the rate of suction, Reynolds number, and Prandtl number. Interesting means of heating and cooling processes of cylinder surface are obtained using different rate of transpiration.
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