Order-disorder phase transition and lipid dynamics in rabbit small intestinal brush border membranes. Effect of proteins

Abstract

The total lipids extracted from brush border membranes form smectic lamellar phases when dispersed in water. 31P broad-band nuclear magnetic resonance (NMR) shows that between body temperature (37 degrees C) and freezing of the solvent, the extracted lipids form bilayers with the lipid molecules undergoing fast anisotropic motion. This is also true for the lipids present in the brush border membrane. The electron spin resonance (ESR) results obtained with various hydrophobic spin probes incorporated in either brush border vesicle membranes or their extracted lipids are consistent with this interpretation. By use of a variety of chemically different spin-labels, the temperature dependence of brush border membranes and their extracted lipids was probed. The temperature dependence of various ESR spectral parameters shows discontinuities that, by comparison with differential scanning calorimetry, are assigned to a lipid thermotropic phase transition. Differential scanning calorimetry shows that the lipid in brush border membranes undergoes a broad, reversible phase transition of low enthalpy between 10 and 30 degrees C, with a peak temperature of about 25 degrees C. Hence, the brush border membrane of rabbit small intestine functions in the liquid-crystalline state, well above the peak temperature and also above the upper limit of the lipid phase transition. Therefore, in itself, the thermotropic lipid phase transition is unlikely to play a physiological role. The low enthalpy of the lipid phase transition, indicative of a lack of cooperativity, is primarily attributed to the relatively high cholesterol content and to heterogeneity in the lipid composition of this membrane [Hauser, H., Howell, K., Dawson, R. M. C., & Bowyer, D. E. (1980) Biochim. Biophys. Acta 602, 567-577].(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of an Integral Protein of the Brush Border Membrane Mediating the Transport of Divalent Metal Ions

“…The value of the activation energy E a ϭ 5.1 kcal/mol derived from the straight-line portion of the Arrhenius plot above 5°C (Fig. 3 B) agrees within the error of the measurement with the activation energy reported for the Na ϩ -dependent D-glucose transporter in the rat BBMVs (Brasitus et al, 1979) but is about half of the value reported by Mütsch et al (1983) for the same protein in rabbit BBM. The metal ion transport above the second break point is characterized by an activation energy of E a ϭ 14.8 kcal/ mol.…”

“…The Arrhenius plot exhibits two break points, one at 5 Ϯ 1°C and another one at 24 Ϯ 1°C. Differential scanning calorimetry, electron spin resonance and fluorescence spectroscopy showed a broad gel-to-liquid crystal transition in both rat (Brasitus et al, 1980) and rabbit BBM (Mütsch et al, 1983). In the latter case this transition covers a temperature range from 10°C to 30°C (Hauser et al, 1982;Mütsch et al, 1983).…”

“…Differential scanning calorimetry, electron spin resonance and fluorescence spectroscopy showed a broad gel-to-liquid crystal transition in both rat (Brasitus et al, 1980) and rabbit BBM (Mütsch et al, 1983). In the latter case this transition covers a temperature range from 10°C to 30°C (Hauser et al, 1982;Mütsch et al, 1983). The two break points in the Arrhenius plot are apparently related to the temperature range of the gel-to-liquid crystal transition: the lower break point occurs 5°C below the onset and the higher one 5°C below the completion temperature of the transition (Fig.…”

“…BBManchored enzymes such as sucrase-isomaltase and lactase have active centers that are located in the aqueous phase rather than within the lipid bilayer of the membrane. Consequently, Arrhenius plots of these enzymes were shown to have no break points (Brasitus et al, 1979;Mütsch et al, 1983). In contrast, membrane-spanning enzymes such as the Ca 2ϩ /Mg 2ϩ -dependent ATPase and the D-glucose transporter exhibit break points in the Arrhenius plot within the temperature range of the thermal lipid transition of the BBM (Brasitus et al, 1979;Mütsch et al, 1983).…”

Cold Adaptation in Ectotherms: Regulation of Membrane Function and Cellular Metabolism

“…2) as detected by independent physical measurements; rates of activity in the fluid phase markedly exceed those in the gel phase (Thilo et al 1977). A few examples include adenyl cyclase activity in plasma membranes of rat hepatocytes (Livingstone and Schachter 1980), glucose transport across brush border membranes of rabbit small intestine (Mutsch et al 1983), succinate oxidation in rat liver mitochondria (Raison et al 1971), and Na+ /H+ -exchange and water transport in human placenta (Illsley et al 1987). Perhaps related to the disruption of catalytic function, freeze-fracture electron micrographs reveal that upon phase separation, smoothfaced regions of the crystallized lipid domain are formed from which integral membrane proteins are excluded.…”