Pterins spectrum

Their physical properties closely resemble those of pterin, which has a basic pKt, of 2.20 and an acidic one of 7.86 associated with N-1 protonation and a hypsochromic shift of the long-wavelength absorption band in the UV spectrum, and N-3 deprotonation effecting a bathochromic shift respectively (Table 4). The xanthopterin (4) and isoxanthopterin types... 

Pterin, 6,7-dimethyl-5,6,7,8-tetrahydro-configuration, 3, 281 conformation, 3, 281 Pterin, 6,7-diphenyl-chlorination, 3, 296 methylation, 3, 297 reduction, 3, 307 Pterin, 6,7-diphenyl-5,6-dihydro-properties, 3, 306 UV spectrum, 3, 279 Pterin, 6-ethyl-5,6,7,8-tetrahydro-configuration, 3, 281 Pterin, 6-formyl-synthesis, 3, 318 Pterin, 6-formyl-5,8-dihydro-synthesis, 3, 306... 

D. gigas AOR was the first Mo-pterin-containing protein whose 3D structure was solved. From D. desulfuricans, a homologous AOR (MOD) was purified, characterized, and crystallized. Both proteins are homodimers with-100 kDa subunits and contain one Mo-pterin site (MCD-cofactor) and two [2Fe-2S] clusters. Flavin moieties are not found. The visible absorption spectrum of the proteins (absorption wavelengths, extinction coefficients, and optical ratios at characteristic wavelengths) are similar to those observed for the deflavo-forms of... 

Evidence for the presence of a pterin cofactor in this enzyme was obtained by Mukund and Adams (282) the fluorescence spectrum of the... 

The absorption band at 384 nm is composed of contributions of the radical species and the second chromophore, whereas the fluorescence spectra with excitation maxima at 398 nm and emission maxima at 470-480 nm are attributed to the pterin alone (146, 155). The 7,8-dihydropterin cofactor, Xmax = 360 nm when free in solution and 390 nm when protein bound, is labile at neutral pH, readily decomposing upon denaturation to form products without significant visible absorption maxima. The photoreduction described above also reduces the second cofactor but in an irreversible manner with complete loss of its fluorescence and visible absorption characteristics (157). Reduction of the blue semiquinone FAD cofactor to the fully reduced form has no effect on the absorption spectrum of the pterin, suggesting that the absorption spectrum of the second cofactor must be independent of the oxidation state of the flavin and that the two cofactors are electronically isolated from each other (157). However, reduction of the flavin radical results in an increase in the fluorescence of the second cofactor, possibly indicating that the flavin radical acts as a potent quencher of fluorescence of the 7,8-dihydropterin. 

Several action spectra have been constructed for phototaxis (and photophobic responses) in Eu lena. They are distinctly different from those measured, e.g., in Chlamydomonas and have been suggested to represent the involvement of flavins and pterins. Fluorometric analysis has indicated that pterins, absorbing in the UV-A range of the spectrum with a maximum near 360 nm, function as antenna pigments. Pterins emit at about 450 nm, which corresponds with one of the maxima for flavin absorption. The fluorescence emission of the flavins can be detected at 520 nm (82). Therefore the final photoreceptor is thought to be a flavin. 

The uv spectrum of the proteinoids displays a broad absorbance. This is due, most likely, to selective absorption by the peptide bonds.This region of absorption is parallel to that of some chromophores and, in particular, to pterin (Figure 2) which has been discovered in the thermal polyamino acids. ... 

Figure lA shows the difference spectrum of the completely reduced beef heart mitochondria. As was shown previously, oxygen had a competing effect on the reduction of ferricytochrome c (Fe +cyto c) by tetrahydro-pterin (PtH4), since ... 

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