C E Whitman | PubMed Health

PubMed1987

Temperature-induced protein conformational changes in barley root plasma membrane-enriched microsomes: I. Effect of temperature on membrane protein and lipid mobility.

A protein spin label and lipid spin probes were used to study the temperature-dependent motion of protein and lipid, respectively, in barley (Hordeum vulgare L. cv Conquest) root plasma membrane-enriched microsomes. Using membranes from seedlings grown at 20 degrees C, the temperature-dependence of the relative motion of membrane surface spin probes and a spin label covalently attached to membrane proteins suggested abrupt changes in the lipid and protein mobilities at about 12 degrees C. Spin probe spin-spin exchange broadening and fluorescent probe eximer formation indicated apparent temperature-induced alterations in probe lateral diffusion within the membrane at about 12 to 14 degrees C. The results suggest the presence of temperature-induced quasicrystalline lipid clusters which may influence the activity of membrane-bound enzymes.

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PubMed1985

Phospholipid composition of a plasma membrane-enriched fraction from developing soybean roots.

Phospholipid polar head group and fatty acid composition were determined for plasma membrane enriched fractions from developing soybean root (Glycine max [L.] Merr. cult. Wells II). Plasma membrane vesicles were isolated from meristematic and mature sections of four-day-old dark grown soybean roots at pH 7.8 and in the presence of 5 millimolar ethylenediaminetetraacetate, 5 millimolar ethyleneglycol-bis (beta-aminoethyl ether)N,N tetraacetic acid, and 10 millimolar NaF. Lipid extracts analyzed for phospholipid composition revealed two major phospholipid components: phosphatidylcholine and phosphatidylethanolmine. Minor phospholipid components identified were phosphatidylinositol, phosphatidylserine, phosphatidylglycerol, and diphosphatidylglycerol. Lipid degradation by endogenous phospholipase D during membrane isolation at pH 6.5 and in the absence of chelating agents and NaF resulted in the recovery of large amounts of phosphatidic acid. Phosphatidylcholine was the principal substrate for phospholipase D.Fatty acid composition was determined for plasma membrane phosphatidylcholine and phosphatidylethanolamine from meristematic and mature root tissue. The fatty acids identified were 16:0, 18:0, 18:1, 18:2, and 18:3. Fatty acid composition varied with both phospholipid class and the developmental stage of the root. Results suggest that differences in the composition of the major phospholipids of plasma membrane from meristemaic and mature root sections occur in the fatty acids and not in the polar head groups. These differences and those found in the composition of the polar head groups of the minor phospholipid components, e.g. phosphatidylglycerol, may be significant for structure-function relationships within the membrane.

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