ISSN:
1573-899X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract The chief phospholipids of the outer segments are phosphatidyl-ethanol-amine, lecithin, and phosphatidyl-serine. The conditions of extraction (temp-erature, solvent) have a substantial effect on the yield and qualitative composition of the extracted phospholipids. After low-temperature (−35C) extraction with a mixture of N-hexane and chloroform (1∶2) 60–80% of the phospholipids of the outer segments were extracted (phosphatidyl-ethanolamine was extracted almost completely, phosphatidyl-serine about 80%, and lecithin about 60%). The Na+ concentration in these extracts was much higher than that of K+, and the Na+/K+ ratio for them was 4. 0, compared with 0. 6 for the initial fractions of the outer segments. Daylight illumination (500 lx, 5–10 min) of a suspension of outer segments in isotonic sucrose solution caused their K+concentration to fall because the cation escaped into the incubation medium. The Na+ concentration in the residue of outer segments was unchanged. Meanwhile the concentration of this cation in low-temperature lipid extracts from outer-segments illuminated earlier was 40% higher than in extracts from darkadapted fractions. Binding of Na+ by lipids of the outer segments during illumination was more marked at OC than at 20C. The concentration of K+, like the total content of phospholipids, in the extracts was unchanged by illumination of the fraction. It is postulated that binding of Na+ by lipids of the outer segments may be directly related to the primary mechanisms of photoreception. A change in active concentrations of cations in individual parts of the structure of the outer segment can take place not only by their migration from one intracellular space into another, but also by a change in the relative proportions of their free and bound forms.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01184804
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