Myoglobin, absorption spectrum

The biochemical activity and accessibility of biomolecule-intercalated AMP clays to small molecules was retained in the hybrid nanocomposites. For example, the absorption spectrum of the intercalated Mb-AMP nanocomposite showed a characteristic soret band at 408 nm associated with the intact prosthetic heme group of the oxidised protein (Fe(III), met-myoglobin) (Figure 8.9). Treatment of Mb with sodium dithionite solution resulted in a red shift of the soret band from 408 to 427 nm, consistent with the formation of intercalated deoxy-Mb. Reversible binding of CO under argon to the deoxy-Mb-AMP lamellar nanocomposite was demonstrated by a shift in the soret band from 427 to 422 nm. Subsequent dissociation of CO from the heme centre due to competitive 02 binding shifted the soret band to 416nm on formation of intercalated oxy-Mb. 

Myoglobin can also bind CO, and sol-gel with entrapped myoglobin can be used as the sensor for CO by taking advantages of the changes in the absorption spectrum due to protein-CO interaction. 

Hb possesses both 4 and 5-coordinate forms as demonstrated by the Raman spectra (Figure 1) and the spj it Soret band of the absorption spectrum (9,36). In contrast, Mb shows only the red Soret component and the Raman lines characteristic of the 5-coordinate form. Thus, myoglobin s R-like structure favors the 5-coordinate form. The R/T difference in affinity for histidine might also be expected to reveal itself in the strength of the Ni-histidine bond. In native Fe hemoglobin, the Fe-histidine bond increases in strength upon conversion from the T to R structure (31,39). 

The absorption spectrum of cytochrome o (128) is also reported in Table 6. In many respects it too is like myoglobin but it reacts with oxygen rather than picking it up. Thus it is a terminal oxidase and not an oxygen carrier. 

Fraunfelder and co-workers [65-68] have found the same relationship in the reduction kinetics of CO and O2 ligand coordination bonds with the complex-forming Fe ions of the heme group myoglobin upon photodissociation of these bonds induced by laser photolysis of 10 s duration. The formation of Fe-CO and Fe-02 bonds after photolysis was registered with a spectrophotometer by restoration of the mother compound absorption spectrum in the wide range of times (10 -10 s) and temperatures (2-300 K). Before photolysis the six-coordinate Fe ion is in the heme plane. The coordination bond break causes not only the ligand shift but also... 

However, low-temperature spectroscopy reveals that the chromophore absorption spectrum is heterogeneously broadened, and Frauenfelder has shown that there is a functional link between the spectral line position and the recombination rate. Agmon and Hopfield pointed out that the protein myoglobin is photolyzed into a strained configuration and must undergo conformational relaxation to reach the true deoxy configuration, and that the recombination rate is slowest in the fully relaxed deoxy... 

Figure 5 A spectral hole in the absorption spectrum of myoglobin complexed with protoporphyrin IX at 7= 1.5 K.

Figure 23-3 Infrared absorbance spectra of the amide regions of proteins. (A) Spectra of insulin fibrils illustrating dichroism. Solid line, electric vector parallel to fibril axis broken line, electric vector perpendicular to fibril axis. From Burke and Rougvie.24 Courtesy of Malcolm Rougvie. See also Box 29-E. (B) Fourier transform infrared (FTIR) spectra of two soluble proteins in aqueous solution obtained after subtraction of the background H20 absorption. The spectrum of myoglobin, a predominantly a-helical protein, is shown as a continuous line. That of concanavalin A, a predominantly (3-sheet containing protein, is shown as a broken line. From Haris and Chapman.14 Courtesy of Dennis Chapman.

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