Karl-Heinz Buchel

The Modification of the Trapping Properties within the Photosynthetic Watersplitting Enzyme System Y

SummaryThe modification of the trapping properties for oxidizing equivalents (holes) within the watersplitting enzyme system Y by chemicals (ADRY agents) has been investigated. It is shown:(1)The ADRY agents decrease significantly the storage life time of the higher trapped hole accumulation states.(2)The acidic NH-or OH-group is a functional indispensable element for substances to be able to act as ADRY agents.(3)The trapping efficiency of the watersplitting enzyme system Y for holes is not correlated with the transmembrane electrochemical gradient.(4)As electron donor for the discharge of the trapped holes acts an andogeneous carrier of the electron transport chain located either between the photosystems I and II respectively or on the reducing side of system I. A special electron donor is not required for the ADRY effect. Based on these properties of the ADRY effect the nature of the traps for the storage of holes within the watersplitting enzyme system Y is discussed.

Sterol Biosynthesis Inhibitors

Sterol biosynthesis inhibitors such as the imidazoles and 1,2,4-triazoles are generally regarded as inhibitors of sterol C-14 demethylation. Neither the MIC values nor the data for direct interaction with the cytochrome P-450 responsible for oxidative C-14 methyl removal, however, fully explain the observed in vivo efficacy. The first generation of azoles, which includes clotrimazole and miconazole, has been supplemented by a second generation, and azoles of the new generation are capable of additional effects on sterol biosynthesis. With the new azoles, for example, delta 5 sterols may accumulate, the accumulation being due to additional sites of inhibition in sterol biosynthesis or to direct membrane-azole interactions. Ketoconazole, itraconazole, and vibunazole are representative of the azoles of the second generation. Finally, a third generation of azoles has been discovered. Azoles of this generation, which include fluconazole, show almost negligible in vitro potency against saprophytically grown fungi but excellent in vivo efficacy. These compounds specifically affect parasitic forms of fungi, thus blocking invasion processes, and interfere directly with the plasma membrane, as shown in leakage experiments. Such secondary effects obviously enhance in vivo potency.