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Coproheme decarboxylase (ChdC) catalyzes the last step in the heme biosynthesis pathway of monoderm bacteria with coproheme acting both as redox cofactor and substrate. Hydrogen peroxide mediates the stepwise decarboxylation of propionates 2 and 4 of coproheme. Here we present the crystal structures of coproheme-loaded ChdC from Listeria monocytogenes (LmChdC) and the three-propionate intermediate, for which the propionate at position 2 (p2) has been converted to a vinyl group and is rotated by 90° compared to the coproheme complex structure. Single, double, and triple mutants of LmChdC, in which H-bonding interactions to propionates 2, 4, 6, and 7 were eliminated, allowed us to obtain the assignment of the coproheme propionates by resonance Raman spectroscopy and to follow the H2O2-mediated conversion of coproheme to heme b. Substitution of H2O2 by chlorite allowed us to monitor compound I formation in the inactive Y147H variant which lacks the catalytically essential Y147. This residue was demonstrated to be oxidized during turnover by using the spin-trap 2-methyl-2-nitrosopropane. Based on these findings and the data derived from molecular dynamics simulations of cofactor structures in distinct poses, we propose a reaction mechanism for the stepwise decarboxylation of coproheme that includes a 90° rotation of the intermediate three-propionate redox cofactor.

Nonlinear optical waveguide elements have to be operated at wavelengths where the waveguide material exhibits minimum linear alpha and higher-order alpha2 is as large as possible. The dispersion of these two quantities has been measured in the wavelength range between 780 and 990 nm. A stable semiintegrated Mach-Zehnder interferometer as well as a spectral broadening set-up were used. The light source was a Ar-pumped tunable Ti:sapphire laser, generating picosecond light pulses. The measurement have been performed on one class of conjugated polymers, substituted poly(phenylenevinylene) (PPV), which are promising candidates for the demonstration of nonlinear switching in waveguide elements. Low-loss waveguides (< 1 dB cm-1) with extreme stability against pulsed optical intensity (up to 16 GW cm-1), allowing for a nonlinear induced phase shift of more than 3 pi have been demonstrated. The nonresonant n2 values are several times 10(exp-14) cm2 W-1 for the two PPV derivates measured. Spati al solutions have been observed the first time in a polymer waveguide.

In a polyconjugated main chain polymer strip waveguide the nonlinear, nonresonant refractive index n2 was measured by monitoring the signal spectrum broadening due to self-phase modulation. The two photon absorption coefficient alpha 2 was obtained by calibrating the inverse transmission measurement. The nonlinear coefficients were determined to be n2=0.85*10-14 cm-2/W and alpha 2=0.08 cm/GW at a wavelength lambda =885.6 nm. The used polymer was poly[1,4-phenylene-1,2-di(phenoxyphenyl)vinylene]. The result is in good agreement with interferometer measurements. The material is suitable for all-optical switching.

In this contribution we report on the generation of 830 W of compressed average power at 78 MHz pulse repetition frequency from an ultrashort pulse fiber chirped pulse amplification system. The pulses are as short as 640 fs.