Chlorins protein complexes

Figure 8 Schematic cross-section of a chloroplast membrane showing an intrinsic protein spanning the membrane, with hydrophilic regions located at the membrane surfaces and a hydrophobic portion shaded) embedded within the non-polar interior of the lipid bilayer. Anderson 55 postulates that the chlorophyll molecules represented above with the hydrophobic portion of the chlorin ring shaded) are located as part of the boundary lipid of a chlorophyll-protein complex (Reproduced by permission from Nature, 1975, 253, 536)...

The ability of MPO to catalyze the nitration of tyrosine and tyrosyl residues in proteins has been shown in several studies [241-243]. However, nitrite is a relatively poor nitrating agent, as evident from kinetic studies. Burner et al. [244] measured the rate constants for Reactions (24) and (25) (Table 22.2) and found out that although the oxidation of nitrite by Compound I (Reaction (24)) is a relatively rapid process at physiological pH, the oxidation by Compound II is too slow. Nitrite is a poor substrate for MPO, at the same time, is an efficient inhibitor of its chlorination activity by reducing MPO to inactive Complex II [245]. However, the efficiency of MPO-catalyzing nitration sharply increases in the presence of free tyrosine. It has been suggested [245] that in this case the relatively slow Reaction (26) (k26 = 3.2 x 105 1 mol-1 s 1 [246]) is replaced by rapid reactions of Compounds I and II with tyrosine, which accompanied by the rapid recombination of tyrosyl and N02 radicals with a k2i equal to 3 x 1091 mol-1 s-1 [246]. 

The highly complex chlorinated pyrrole-containing macrolide colubricidin A (1626) is produced in cultures of an unidentified Streptomyces species (1595). This metabolite displays excellent activity against Gram-positive bacteria. The Dominican sponge Spirastrella coccinea produces spirastrellolide A (1627), which is a potent and selective inhibitor of protein phosphatase 2A (1596) (revised later (1597)). 

It is my pleasure to introduce Volume 73 of Annual Reports on NMR. In common with previous volumes, it contains reports from a few of the many areas of NMR active research. The first contribution is by T. W. T. Tsai and J. C. C. Chan on Recent Progress in the Solid-State NMR Studies of Biomineralization the topic Recent Advances in the NMR Spectroscopy of Chlorine, Bromine and Iodine is covered by B. J. Butler, J. M. Hook and J. B. Harper M. D. Lingwood and S. Han report on Solution-State Dynamic Nuclear Polarization the topic of Solid-State NMR of Membrane Proteins Moving Towards Greater Complexity is covered by L. K. Thompson Chromatographic NMR is the topic chosen by S. Caldarelli the final contribution on Kinetic Monte Carlo Simulation of DNMR Spectra is by Z. Szalay and J. Rohonczy. My grateful thanks are due to all of these reporters for their interesting and timely contributions. 

Proteins, due to the complexity of their chemical structures, undergo oxidative modifications in subsequent stages which depend both on the presence of oxidation-susceptible groups and on steric availability of these groups for oxidant attacks (S25). Some oxidative structural modifications produced in proteins are common in various oxidants. Some modifications, such as chlorinated and nitrated protein derivatives produced in reactions with hypochlorite, peroxynitrite, and nitric dioxide, are specific for the oxidants employed. Certain oxidative protein modifications, such as interchain or intrachain disulfide bond formation or thiolation, are reversible and may be reduced back to the protein native form when oxidative stress is over (Dl). Other changes, such as sulfone formation, chlorination, and nitration, are irreversible and effect protein denaturation and promote its subsequent degradation. 

PS II and PS I, and the 28 kDa protein of LHC II, show a number of possible a-helical regions in each case (see Chapter 11). Given the size of the chlorin ring (= 15 X 15 A) and the fact that each apoprotein binds many pigment molecules, it is not surprising that these apoproteins are associated with the membrane o-helical regions, since protease digestions of intact thylakoids or vesicles do not release any of the chlorophyll of the PS II complex [27], the PS I complex [28,29] or LHC II [27,28], Moreover, as neither the chlorophyll or xanthophyll molecules of LHC II are accessible to proton attack, they are likely to be located within the hydrophobic interior of the membrane [30],... 

---