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Biomedical subjects

J B Mudd

Publications and source records attributed to J B Mudd.

At least 37 records · Page 2Linked to original sources
PubMed1982

Phosphatidylglycerol synthesis in spinach chloroplasts: characterization of the newly synthesized molecule.

Intact chloroplasts from spinach (Spinacia oleracea L., hybrid 424) readily incorporate [(14)C]glycerol-3-phosphate and [(14)C]acetate into diacylglycerol, monoacylglycerol, diacylglycrol, free fatty acids (only when acetate is the precursor), phosphatidic acid, phosphatidylcholine, and most notably phosphatidylglycerol. The fraction of phosphatidylglycerol synthesized is greatly increased by the presence of manganese chloride in the reaction mixture. Glycerol-3-phosphate-labeled phosphatidylglycerol is equally labeled in the two glycerol moieties of the molecule. Acetate-labeled phosphatidylglycerol is equally labeled in both acyl groups. Position one contains primarily oleate, linoleate and small amounts of palmitate. Position two contains primarily palmitate. No radioactive trans-Delta(3)-hexadecenoate was detected. The labeling patterns indicate that the radioactive phosphatidylglycerol is the product of de novo chloroplast lipid biosynthesis and furthermore, phosphatidylglycerol may be a substrate for fatty acid desaturation.

Journal Article↗
PubMed1982

Localization of Filipin-Sterol Complexes in the Membranes of Beta vulgaris Roots and Spinacia oleracea Chloroplasts.

Filipin was used as a cytochemical probe for membrane sterols in the root storage tissue of the red beet Beta vulgaris L. and the chloroplasts of Spinacia oleracea L. In unfixed beet tissue, filipin lysed the cells. Freeze-fracture replicas revealed that the filipin-sterol complexes were tightly aggregated in the plasma membrane, while in thin section the complexes corrugated the plasma membrane. If the cells were fixed with glutaraldehyde prior to the filipin treatment, the cell structure was preserved. Filipin-induced lesions were dispersed or clustered loosely in the plasma membrane. A few filipin-sterol complexes were observed in the tonoplast. In spinach chloroplasts, filipin-sterol complexes were limited to the outer membrane of the envelope and were not found in the inner membrane of the envelope or in the lamellar membranes. If the filipin-sterol complexes accurately mapped the distribution of membrane sterols, then sterol was located predominantly in the plasma membrane of the red beet and in the outer membrane of the chloroplast envelope. Furthermore, the sterol may be heterogenously distributed laterally in both these membranes.

Journal Article↗
PubMed1981

Lipid phase separations and intramembranous particle movements in the yeast tonoplast.

The tonoplast of Saccharomyces cerevisiae contains regions depleted of intramembranous particles as the cells enter stationary phase. Freeze-fracture studies on intact cells from this growth stage show that a dispersed particle distribution predominates if the cell temperature is raised to 40 degrees C but that particle-depleted areas prevail at or below the cell growth temperature of 30 degrees C. Tonoplasts of isolated vacuoles also contain particle-depleted regions. Differential thermal analysis of lipids extracted from isolated vacuoles show an endothermic transition which encompasses the cell growth temperature. These results suggest that the tonoplast at this stage contains patches of gel-phase lipid and that these patches correspond to the intramembranous particle-depleted areas of the freeze-fractured tonoplast.

Cell Membrane↗
PubMed1980

Effect of steryl glycosides on the phase transition of dipalmitoyl lecithin.

The phase transition of dipalmitoyl lecithin, measured by thermal analysis, was eliminated by the plant sterol, sitosterol, and by the derivatives steryl glucoside and acylated steryl glucoside, which were isolated from soybean lipids.When digitonin was added to dipalmitoyl lecithin-sterol mixtures, in amounts equimolar to sterol, the phase transition of the phospholipid was revealed presumably because of the formation of a sterol complex. When digitonin in molar excess of sterol was added, the endothermic peak disappeared again.

Journal Article↗
PubMed1980

Inhibition of steryl glycoside biosynthesis by acyl coenzyme a and by digitonin.

ATP, GTP, CoA, Mg(2+), and Mn(2+) did not inhibit biosynthesis of steryl glycoside and acylated steryl glycoside when added singly to enzyme preparations from spinach leaves. The combination of ATP (but not GTP), CoA, and Mg(2+) or Mn(2+) caused marked inhibition, especially of steryl glycoside biosynthesis, when reaction mixture concentrations of the additions were 0.2 millimolar. Inhibition was attributed to acyl-CoA and could be reproduced by palmitoyl-CoA. The inhibition could be partially prevented by bovine serum albumin. The effects of palmitoyl-CoA were distinct at 10 micromolar, and 50% inhibition of biosynthesis was observed at 40 micromolar.Digitonin (0.6 millimolar) stopped steryl glycoside biosynthesis but permitted the conversion of steryl glycoside to acylated steryl glycoside, thus eliminating the possibility that acylated steryl glycoside is formed from sterol + an acyl-glucose donor.

Journal Article↗
PubMed1979

Linoleate and alpha-linolenate synthesis by isolated spinach (Spinacia oleracea) chloroplasts.

Diacylgalactosylglycerol synthesis was a prerequisite for the incorporation of [1-14C]-acetate into linoleate and alpha-linolenate of isolated spinach (Spinacia oleracea) chloroplasts. Oleate at position 1 of diacylgalactosylglycerol was desaturated to linoleate and alpha-linolenate both in the light and in the dark. Some desaturation of palmitate was also observed after prolonged incubations.

Acetates↗
PubMed1979

Comparison of the membrane composition of Spiroplasma citri and the corn stunt Spiroplasma.

Components of membranes isolated from Spiroplasma citri and corn stunt spiroplasma grown at 28 degrees C were analyzed. On a protein basis, lipid phosphorus was lower and cholesterol was higher in S. citri. Only minor differences between the two species were found in fatty acid composition, reduced nicotinamide adenine dinucleotide diaphorase, and adenosine triphosphatase.

Bacterial Proteins↗
PubMed1978

Partial characterization of steryl ester biosynthesis in spinach leaves.

Acetone powders of a 20,000g pellet fraction from spinach leaves (Spinacia oleracea L.) synthesized [4-(14)C]cholesteryl esters when incubated with [4-(14)C]cholesterol. The reaction was inhibited by digitonin. There was a reciprocal relationship between the decline of label in cholesterol and its incorporation into cholesteryl ester, indicating that free cholesterol was the direct precursor for cholesteryl ester biosynthesis. The hydrolysis of cholesteryl [1-(14)C]palmitate into free cholesterol and [1-(14)C]palmitate was not detected in these acetone powder preparations. Exogenous cholesteryl palmitate had no effect on the esterification of [4-(14)C]cholesterol. The data indicate that an esterase-type mechanism was not involved in the biosynthesis of these steryl esters. Label from [1-(14)C]palmitoyl-CoA was incorporated into steryl esters when incubated with spinach leaf acetone powder preparations. The optimal buffer for steryl ester biosynthesis was 2-(N-morpholino)ethanesulfonate and the optimal pH was 6. Iodoacetamide, N-ethylmaleimide, and dithiothreitol had no effect on the esterification reaction. Ethylenediaminetetraacetate, MgCl(2), CaCl(2), MnCl(2), and ZnSO(4) inhibited at concentrations of 10 to 30 mm.

Journal Article↗
PubMed1978

Subcellular distribution of steryl ester biosynthesis in spinach leaves.

Higher steryl ester biosynthetic activities were obtained with Triton X-100-phosphatidylcholine-cholesterol mixed micelles than with Tween 80-phosphatidylcholine-cholesterol mixed micelles when incubated with spinach leaf (Spinacia oleracea L.) acetone powder preparations. The best incorporation of [4-(14)C]cholesterol into [4-(14)C]cholesteryl ester was obtained with a Triton X-100-phosphatidylcholine-cholesterol (10:1:1, w/w) mixed micelle system. This mixed micelle system, however, required 1,2-dipalmitin and fatty acid-free bovine albumin for optimal activity. The reaction exhibited a diglyceride specificity since the dipalmitin requirement could be replaced with neither 1-monopalmitin nor tripalmitin. Significant amounts of steryl ester biosynthetic activity were detected in the chloroplast (1,000g pellet), mitochondrial (3,000g pellet), and microsomal (20,000g and 88,000g pellet) fractions. Little activity was detected in the water-soluble (88,000g supernatant) fraction. The highest specific activity occurred in the 88,000g pellet. The 88,000g supernatant contained a heatstable, water-soluble substance that was required for optimal steryl ester biosynthesis in all of the pellet fractions. This factor was not lost during extensive dialysis but was destroyed by ashing, indicating that it was large and organic. Silver nitrate thin layer chromatography indicated that 60% of the biosynthesized steryl esters contained saturated fatty acids in the absence of 1,2-dipalmitin and that 83% contained saturated fatty acids in the presence of 1,2-dipalmitin.

Journal Article↗