| Autor: |
Bishop, David G., Op Den Kamp, Jos A.F., Van Deenen, Laurens L.M. |
| Předmět: |
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| Zdroj: |
European Journal of Biochemistry; 11/1/77, Vol. 80 Issue 2, p381-391, 11p |
| Abstrakt: |
The distribution of phospholipids in the protoplast membrane of Bacillus subtilis has been studied by comparing the effects of treatment with phospholipase C or trinitrobenzenesulphonic acid on intact protoplasts or membranes derived from them. After 2 h treatment of protoplasts at 37 °C with phospholipase C (B. cereus), 45-50% of the membrane phospholipid has been hydrolyzed, including 90% of the phosphatidylethanolamine and 70-80% of the lysylphosphatidylglycerol, but no lysis of the protoplasts can be detected. Complete hydrolysis of phosphatidylethanolamine and lysylphosphatidylglycerol by phospholipase C is obtained in isolated membranes at a rate greater than in intact protoplasts. The rate and extent of hydrolysis by phospholipase C in both protoplasts and membranes is strongly temperature-dependent and part of this effect is ascribed to phase separations in the membrane lipid reducing accessibility of the substrates. About 60% of the aminophospholipids in intact protoplasts are labelled by exposure to trinitrobenzenesulphonic acid and this level increases to only 70% in isolated membranes. It is concluded that the introduction of the bulky head group into both protein and lipid during trinitrobenzenesulphonic acid labelling precludes the reaction proceeding to completion. The results do not permit an unequivocal distribution of the phospholipids between the inner and outer halves of the bilayer. It appears however that at least 60% of the phosphatidylethanolamine is located in the outer monolayer, and under conditions where lysylphosphatidylglycerol is accumulated, that at least 60% of this lipid is also in the outer monolayer. Furthermore, the membrane appears to contain the capacity for transbilayer movement (flip-flop) of at least the aminophospholipids and this capacity is expressed when the composition of the outer half of the bilayer is modified by treatment with phospholipase C. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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