Sarcoplasmic reticulum: VIII. Use of 8-anilino-1-naphthalene sulfonate as conformational probe on biological membranes

Abstract

The fluorescence of 8-anilino-1-naphthalene sulfonate (ANS) 3 3 The following abbreviation was used: ANS, 8-anilino-1-naphthalene sulfonate. is enhanced by skeletal muscle microsomes and micellar dispersions of phospholipids. The magnitude of the enhancement is a unique function of the ionic composition, rising with the concentration of cations according to a titration curve. The effect of cations might reflect the increased hydrophobic character of the membrane or the increased binding of ANS, induced by cations. The optimum pH for the ANS fluorescence in the presence of microsomes or lecithin is at pH 1–4 and at pH 7.3 a complex temperature dependence was observed with indications of a transition at 35–40 °. Treatment of microsomes or lecithin with phospholipase C causes a decrease of ANS fluorescence while trypsin digestion had little or no effect. Polymyxin B, a circular polypeptide, inhibits the ATPase activity and Ca 2+ transport of muscle microsomes accompanied by a large increase in fluorescence enhancement in the presence of ANS. Tyrocidine also inhibited the biochemical functions while gramicidin was less effective. Polyene antibiotics were generally without effect. These observations indicate that caution is required in the evalution of ANS fluorescence data in terms of conformational changes in membrane proteins alone, since the contribution of phospholipids to the fluorescence is significant.