Type II spectrum

ISO ms and finally slower disappearance with formation of the fully reduced enzyme. But the regrowth of the type II spectrum is of a rate comparable to the reduction of the type III Cu(II) site and consistent with the participation of the type II ligand binding site in the reduction of the type III pair. 

Choyke and Patrick reported a well resolved sharp line spectra between 2.10 and 2.35 eV in Al-doped Lely-grown crystals of cubic SiC [77]. They attributed these sharp lines to the recombination of close DAPs, where the N replaces C and Al replaces Si (Type II spectrum). These lines were resolved up to shell m = 80, and an extrapolation to infinite separation yielded an accurate value of the minimum photon energy, Emin = 2.0934 eV. If we use the value of Eg = 2.403 eV, at 4.2 K [77], we obtain from Eqn (2) ... 

An IBSCA-spectrum (Fig. 4.48) consists of many peaks in the visible range (250-900 nm). Every peak can be related to an process of electron de-excitation of a sputtered particle from a higher to a lower state, for the more dominant peaks to the ground state. There are, in principle, two major types of peak family type I - photons emitted from excited sputtered secondary neutrals and type II - photons emitted from excited sputtered secondary ions (single charged). 

There are four disulfide bonds in short-chain (Type I) neurotoxins. This means that there are eight half-cystines. However, all Hydrophiinae toxins have nine halfcystines with one cysteine residue. An extra cysteine residue can be readily detected from the Raman spectrum as the sulfhydryl group shows a distinct S-H stretching vibration at 2578 cm" Some Laticaudinae toxins do not have a free cysteine residue as in the cases of L. laticaudata and L. semifasciata toxins. In long toxins (Type II) there are five disulfide bonds (Table III). 

Many multiple copper containing proteins (e.g., laccase, ascorbate oxidase, hemo-cyanin, tyrosinase) contain so-called type III copper centers, which is a historical name (cf. Section 5.8 for type I and type II copper) for strongly exchange-coupled Cu(II) dimers. In sharp contrast to the ease with which 5=1 spectra from copper acetate are obtained, half a century of EPR studies on biological type III copper has not produced a single triplet spectrum. Why all type III centers have thus far remained EPR silent is not understood. 

Type II. Deeper-seated and/ or longer-lived systems, also with a wide spectrum of whole rock ratios, but with equilibrated ratios among coexisting... 

The CD of (3-turns has been characterized1127 by using the peptides c(-L-Ala-L-Ala-Aha-) as a model for a type I turn and c(-L-Ala-D-Ala-Aha-) for a type II turn. The CD spectra for these two peptides are shown in Figure 5. The spectrum for the type I turn is of class C and that for the type II turn is of class B. The latter result is consistent with the calculations of Woody, 125 but the former result is not. Moreover, explicit calculations for the low-energy conformers1127 predicted a class B spectrum for type I and a class C spectrum for type II. However, using a classical dipole interaction model 128129 Sathyanarayanan and Applequist 130 obtained qualitative agreement with experiment for these two model systems. 

Further support for this assignment of CD spectra for the two most common types of (3-tums has been provided by studies of cyclic hexapeptides. 92,131132 The prediction of a class C spectrum for the type IT turn was verified by studies of cyclic peptides with the o-Xaa -L-Pro sequence. 131-133 A peptide with the sequence L-Pro-D-Ala, expected to have a variant of a type II turn, 126 was found 134 to have a class C spectrum (mirror image of a class C spectrum), in accordance with predictions. 125 A type VI turn, with a d.v-Xaa -Pro bond has been studied in c(-L-Phe-L-Pro-Aha-) and found to have a strong negative band at -212 nm, 133 but data below 200 nm were not reported. Of course, there may be significant aromatic contributions in the spectrum of this peptide. 

Gramicidin S is a cyclic decapeptide with a characteristic CD spectrum that qualitatively resembles that of an a-helixj185-189 but numerous studies described below strongly support the structure predicted by Hodgkin and O ugh ton11751 and by Schwyzer et alJ176l in which 13-turns (type II ) at the D-Phe-L-Pro sequences link two extended tripeptide sequences (Val-Orn-Leu) that form an antiparallel (3-structure. 

Based upon theoretical calculations, it was 31,190 proposed that the negative nut band is largely due to the antiparallel P-sheet region, whereas the D-Pro residues are responsible for the negative 207 nm band. It has also been proposed11251 that the two type II p-tums are primarily responsible for the entire a-helix-like spectrum of gramicidin S. 

Type II substrates are compounds such as nitrogenous bases, with sp2 or sp3 nonbonded electrons. These bind to iron and give rise to a 6-coordinated, low-spin hemoprotein. Such compounds may also be inhibitors of cytochromes P-450. The spectrum shows a peak at 420 to 435 nm and a trough at 390 to 410 nm in the difference spectrum. 

Grassian and Pimentel (210) prepared such surface groups by thermal decomposition of cis- and frans -dichloroethenes at temperatures >200 K or by their photolysis at 110 K on Pt(lll). An ethyne type B spectrum was obtained, as had also been obtained from the direct low-temperature adsorption of ethyne on this surface (Section II.B.l). 

But the evidence is not limited to remnants nitrogen-rich material has in fact been detected in three Type II SN in action. Fransson et al. (1984) derived a very large N/C ratio from the ultraviolet spectrum of 1979C in M100 shortly after maximum. Niemela, Ruiz, and Phillips (1985) observed a WN-like optical spectrum from 1983K in NGC 4699 in unprecedented pre-maximum coverage. 

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