Kinetic factors, protein folding

The key question we want to answer is what are the intrinsic sequence dependent factors tliat not only detennine tire folding rates but also tire stability of tire native state It turns out tliat many of tire global aspects of tire folding kinetics of proteins can be understood in tenns of tire equilibrium transition temperatures. In particular, we will show tliat tire key factor tliat governs tire foldability of sequences is tire single parameter... 

There are obvious similarities between the crystal structure prediction problem and the protein folding prediction problem. Both problems involve unsolved questions regarding the choice of force field, the existence of many almost equi-energetic minima in a multi-dimensional energy space, and the relative importance of thermodynamic and kinetic factors, including possible... 

The design and study of the replicating system was based on the simple a-helical coiled-coil protein folding motif, for which the factors contributing to the thermodynamic and kinetic stability of the helical ensembles are well... 

A similar kinetic approach has been used to measure the specific activity of rat liver cytosol or of protein fractions obtained during the purification of SCP2 [21]. As with purified SCP2, the velocity of cholesterol formed is a hyperbolic function of the amount of cytosol protein present. As before, a straight line is obtained when the velocity of cholesterol formation is plotted as a function of cholesterol formed per mg of rat liver cytosol [21]. The purification factor for SCP2 can be calculated from X intercept for rat liver cytosol/2f intercept for purified SCP2. Using this approach [21], a purification factor of 1300-1400-fold was obtained. 

Thiosulfonate reductase has been purified approximately 50-fold from Chlorella (Schmidt, 1973). In addition to catalyzing the reduction of the sulfonate moiety of GS-SOj by Fd d, it also catalyzes the reduction of dithionite to free sulfide using methylviologen. Schmidt (1973) found that the protein fraction which was labeled by GS- SOj in the absence of Fd,ed could be separated from thiosulfonate reductase and that the labeled protein in turn could be resolved into unlabeled protein and a labeled low molecular weight factor. When this factor was supplied to purified enzyme and activity measured by the dithionite/methylviologen assay, the activity was enhanced about threefold. No details of the kinetics of the presumed physiological reaction with bound sulfite and Fdrej are currently available. 

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