L-a- lecithin

Fig. 4. A, Histogram of single channel conductances, y, of Gramicidin A in diphytanoyl L-a-lecithin/n-decane membranes for 1 M KC1, 130 mV potential and 40 °C. Note that single channel conductance is simply the single channel current, i , divided by the applied potential. Reproduced from reference 12) with permission.

B, Histogram of channel lifetimes for Gramicidin A in diphytanoyl L-a-lecithin/n-decane membranes for 1 M KC1, 130 mV applied potential and 15 °C. 

Dimyristoyl-sn-glycero-3-phosphocholine monohydrate (dimyristoyl-L-a-lecithin)... 

Dimyristoyl-sn-glycero-3-phosphochoIine monohydrate (dimyristoyl>L a>lecithin)... 

Baer (1953) has recorded the spectra of pure dimyristoyl, dipalmitoyl, and distearoyl L-a-lecithins. Baer et al. (1952) have also recorded spectra of L- -cephalins, namely, the same kinds of fatty acid derivatives. The spectra have differences, although this is not true for the corresponding straight-chain fatty acids. In the region from 870 to 714 cm" several large differences occur. 

PhosphoHpase A, which is inactive towards lysolecithin (Fairbairn 1945), is capable of removing both saturated and unsaturated fatty acids from lecithins, but at different rates (Hanahan, Rodbell and Turner 1954, Long and Penny 1957). Long and Penny (1957) showed that the enzyme can remove fatty acid from both natural and synthetic L-a-lecithins, but not from D-a-lecithins. The effect of the enzyme on a series of synthetic substrates was investigated by van Deenen and de Haas (1963). 

The technique used for kinetic characterization of lipase activity across a range of pH and temperature values has been described [3-5], The activity was measured in a sodium caseinate (6.0 mg/ml)/L-a-lecithin (0.5 mg/ml) emulsion base using pH-stat. The emulsion base (40 ml) was added to the lipid which had been weighed into a dry, plastic titrator cup and the mixture was sonicated until it became homogeneous. The enzyme solution (50-100 pi, 5 mg/ml) was added and the release of carboxylic acid was determined by titration with 0.01 M NaOH which had been standardized against potassium hydrogen pthalate. 

Horse heart cytochrome , L-a-lecithin from soybean and valinomycin were from Sigma Chemicals, St. Louis, MO 2,3-dimethoxy-5-methyl-l,4-benzo-quinone (UQq) from Trans World Chemicals, Washington and lauryldimethyl-ammonium-N-oxide (LDAO) from Onyx Chemical Comp., Jersey City, NJ. 

RC s from Rhodopseudomonas sphaeroides R-26 were isolated and stored as described previously (Feher, Okamura, 1978). These will be referred to as LDAO-containing RC s. Part of the RC s were treated with Bio-Beads SM-2 (25°C, 3 h, 10% w/v). This treatment removes 66% of the LDAO, originally present in the suspension (as measured with [ C]LDAO) of which more than 90% was bound to the RC s. These RC s were stored in 200 mM KCl and will be referred to as LDAO-depleted RC s. Asolectin was isolated from L-a-lecithin from soybean and stored in an inert atmosphere at -40°C. 

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