1064 NM FT-RAMAN SPECTRA OF HOG KIDNEY MITOCHONDRIAL OUTER MEMBRANES - EFFECTS OF NACL AND TEMPERATURE ON 1100 CM(-1) REGION SPECTRA

In order to obtain the experimental basis for the cause of the previou sly reported intensity decrease of the 1080 cm(-1) band in the presenc e of NaCl, FT-Raman spectra were measured with 1064 nm excitation for aqueous dispersions of hog kidney mitochondrial outer membrane prepara tions in phosphate and Tris-HCl buffer (pH 7.5) in the absence and pre sence of NaCl. It was found that the relative intensity of the similar to 1084 cm(-1) Raman band with respect to the similar to 1064 cm(-1) band decreased considerably in the presence of NaCl in phosphate buffe r and that the intensity decrease in the presence of NaCl was not appr eciable in the spectrum in Tris-HCl buffer, It was also found that the presence of NaCl decreased the relative intensities of the similar to 1126 cm(-1) band with respect to the similar to 1064 and similar to 1 134 cm(-1) bands in both phosphate and Tris-HCl buffer. The spectral c hanges in the same region due to the temperature increase were studied for the membrane preparation of ultracentrifuged pellets for the eluc idation of the vibrational assignments, It was found that the intensit y ratio of the 1084 cm(-1) band with respect to the similar to 1064 cm (-1) band was increased with a temperature increase from 8 to 20 degre es C. An unexpected increase was observed in the relative intensity of the similar to 1126 cm(-1) band with respect to the similar to 1064 c m(-1) band with temperature elevation. It was concluded that the decre ase in I-1084/I-1064 in phosphate buffer (pH 7.5) in the presence of N aCl could be attributed to the decrease in the gauche conformation of phospholipid acyl chains as predicted previously, The NaCl-caused decr ease of the gauche conformation was found to be small in Tris-HCl buff er (pH 7.5), The increase in I-similar to 1126/I-similar to 1064 in th e temperature increase experiment was interpreted in terms of a fairly large contribution of another chain conformation containing gauche bo nds, the so-called almost fully extended form against the fully extend ed form, i.e. all-trans conformation, to the similar to 1126 cm(-1) Ra man band in the fluid state, in which the usual natural biomembranes e xist. The observed decrease in I-similar to 1126/I-similar to 1064 and I-similar to 1126/I-similar to 1134 in the presence of NaCl in both p hosphate and Tris-HCl buffers could result from a decrease in this con formation in the acyl chains due to the interchain tighter packing ind uced by the non-specific screening effect on the membrane surface char ges in the presence of NaCl. (C) 1997 John Wiley & Sons, Ltd.