Myoglobin conformational substrates

Selected entries from Methods in Enzymology [vol, page(s)] Application in fluorescence, 240, 734, 736, 757 convolution, 240, 490-491 in NMR [discrete transform, 239, 319-322 inverse transform, 239, 208, 259 multinuclear multidimensional NMR, 239, 71-73 shift theorem, 239, 210 time-domain shape functions, 239, 208-209] FT infrared spectroscopy [iron-coordinated CO, in difference spectrum of photolyzed carbonmonoxymyo-globin, 232, 186-187 for fatty acyl ester determination in small cell samples, 233, 311-313 myoglobin conformational substrates, 232, 186-187]. 

The temperature dependence of has been investigated in detail with myoglobin [202]. Diffraction studies at four temperatures between 220 and 300 K show the structure to be composed of a condensed core around the haem with displacements of the order of 0.04 A, which are temperature sensitive, and a semiliquid region towards the outside with mean square displacements 0.04-0.25 A, which are essentially temperature independent. The movements of the surface residues point to a possible pathway to the haem group. More detailed analysis at 80 K with crystals cooled by flash-freezing without the use of cryoprotectants showed a decrease in overall B from 14 A at 300 K to 5 A at 80 K [203]. Analysis of individual temperature factors showed that 46 out of the 153 residues in myoglobin had average B factors that extrapolated to zero at 0 K (i.e., arose from thermal vibrations alone). The temperature vibration of the remainder of the protein was consistent with the notion that conformational substrates could be frozen out at low temperatures. An additional 51 residues could be modelled with a linear dependence on temperature but with... 

One example of this possible existence of a hierarchy of receptor states has been discussed by Frauenfelder (1988). He reviewed studies on the binding of substrates and ligands to myoglobin. The process follows a power law, characterizing the protein as a complex system. Nuclear magnetic resonance (NMR) analyses revealed a number of conformational substates. 

When the substrate (R-C-H) enters the active site pocket, a high-spin Fe(III) complex forms due to small changes in the conformation of the peptide or loss of the water ligand. This form is 0.12 V more easily reducible than the resting enzyme and therefore favors the reduction to high-spin Fe(II), which then forms the Oj complex similar to myoglobin. Precedent for the n-cation radical Fe=0 species comes from the more stable and well-characterized intermediate, of... 

The lattice can be made to conform to the shape of the molecule which is represented. We were interested in following differences in unfolding between enzyme and enzyme-substrate (or enzyme-inhibitor) complex, c.q. between apoprotein and protein. X-ray crystallographic studies have shown that many enzymes have a cleft which can accomodate a substrate molecule. Similarly, since myoglobin has a compact... 

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