284 - H. Halobium : I. In vitro studies

Abstract

1. Purple membrane fragments (PM) from H. halobium were incorporated into lipid membranes either directly or via liposomes. A photoresponse was detected when liposomes containing PM were fused with lipid membranes. Low—resistance membranes or membranes shunted with an external resistor of 10 9 ohms showed decay of the initial light response to some equilibrium value in the light in both presence and absence of octadecylamine. The light response could be abolished by the addition of a sufficient amount of triethylamine to either side of the membrane. 2. The photovoltage action spectra of bilayer lipid membranes containing PM either directly or via liposomes were measured, and found to follow the absorption spectrum of bacteriorhodopsin. 3. Liposomes containing bacteriorhodopsin (BR) in PM extract of H. halobium were fused to one side of planar lipid membranes. The photopotential resulting from flash excitation rose and fell as the sum of three exponentials with time constants for the leading edge of 30 ± 10 μs and 35 ± 10 ms. The decay time constant of the photopotential was 840 ms, a value consistent with the membrane time constant given by the membrane dark resistance and capacitance.