Mn-porphyrins in a four-helix bundle participate in photo-induced electron transfer with a bacterial reaction center.

Hybrid complexes incorporating synthetic Mn-porphyrins into an artificial four-helix bundle domain of bacterial reaction centers created a system to investigate new electron transfer pathways. The reactions were initiated by illumination of the bacterial reaction centers, whose primary photochemistry involves electron transfer from the bacteriochlorophyll dimer through a series of electron acceptors to the quinone electron acceptors. Porphyrins with diphenyl, dimesityl, or fluorinated substituents were synthesized containing either Mn or Zn. Electrochemical measurements revealed potentials for Mn(III)/Mn(II) transitions that are ~ 0.4 V higher for the fluorinated Mn-porphyrins than the diphenyl and dimesityl Mn-porphyrins. The synthetic porphyrins were introduced into the proteins by binding to a four-helix bundle domain that was genetically fused to the reaction center. Light excitation of the bacteriochlorophyll dimer of the reaction center resulted in new derivative signals, in the 400 to 450 nm region of light-minus-dark spectra, that are consistent with oxidation of the fluorinated Mn(II) porphyrins and reduction of the diphenyl and dimesityl Mn(III) porphyrins. These features recovered in the dark and were not observed in the Zn(II) porphyrins. The amplitudes of the signals were dependent upon the oxidation/reduction midpoint potentials of the bacteriochlorophyll dimer. These results are interpreted as photo-induced charge-separation processes resulting in redox changes of the Mn-porphyrins, demonstrating the utility of the hybrid artificial reaction center system to establish design guidelines for novel electron transfer reactions.

[Effect of nifedipine on fetal heart rate in pre-eclamptic patients]. / Efecto de la nifedipina sobre la frecuencia cardiaca fetal en pacientes preeclámpticas.

From March 1st to October 31, 1989, we studied 23 women with diagnosis of severe preeclampsia, the gestational age in all of them was at least 34 weeks. A tococardiograph registry was obtained during 20 minutes prior to any management, after that a standardized management was started; nifedipine 10 mg sublingual was administered, and 20 minutes later, a new registry was obtained. In spite of a significative descent of arterial pressure, we did not find any significative change in the fetal heart rate, accelerations, variability, or in the fetal motility.