Membrane fluidity changes in goat sperm induced by cholesterol depletion using beta-cyclodextrin.

Cholesterol efflux from membranes promotes acrosome reaction in goat spermatozoa. In 1 h of incubation of sperm in the presence of beta-cyclodextrin (beta CD), all the interchangeable cholesterol is desorbed from sperm membranes, although acrosome reaction is fully accomplished only after 3-4 h of incubation, as previously published. In the present paper we investigate the effect of cholesterol removal from mature goat spermatozoa on the overall membrane "fluidity" of live cell membranes and of liposomes from sperm lipid extracts.

Structural and functional implications of the instability of the ADP/ATP transporter purified from mitochondria as revealed by FTIR spectroscopy.

The ADP/ATP transporter shows a high instability when solubilized, making it difficult to obtain functional protein with sufficient purity for long-term spectroscopic studies. When solubilized in the detergent dodecyl maltoside the protein is in equilibrium between the so-called CATR and BA conformations and in a few hours it becomes nonfunctional, unable to bind either its inhibitors or its substrates. By Fourier transform infrared spectroscopy, we studied the structural changes involved in this denaturation process.

Study of amide-proton exchange of Escherichia coli melibiose permease by attenuated total reflection-Fourier transform infrared spectroscopy: evidence of structure modulation by substrate binding.

The accessibility of Escherichia coli melibiose permease to aqueous solvent was studied following hydrogen-deuterium exchange kinetics monitored by attenuated total reflection-Fourier transform infrared spectroscopy under four distinct conditions where MelB forms different complexes with its substrates (H(+), Na(+), melibiose). Analysis of the amide II band upon (2)H(2)O exposure discloses a significant sugar protection of the protein against aqueous solvent, resulting in an 8% less exchange of the corresponding H(+)*melibiose*MelB complex compared with the protein in the absence of sugar. Investigation of the amide I exchange reveals clear substrate effects on beta-sheet accessibility, with the complex H(+)*melibiose*MelB being the most protected state against exchange, followed by Na(+)*melibiose*MelB.