Rate Of Phospholipid Turnover Research Articles

High turnover rate of free phospholipids in soil confirms the classic hypothesis of PLFA methodology

Phospholipid fatty acid (PLFA) analysis has been widely used to study soil microbial community structure. Soil PLFAs are taken to be indicative of living organisms since phospholipids are assumed to rapidly degrade after cell death. However, the turnover rate of phospholipids has never been accurately quantified. For this purpose, a short incubation experiment was conducted by amending paddy soil with extracted phospholipids, using the 13C labeling technique and PLFA analysis to quantify phospholipid degradation. Both bacterial (Methylocystis sp. and Escherichia coli) and fungal (Simplicillium subtropicum) phospholipids had high turnover rates. The half-life (t½) for different phospholipids ranged from 14 to 27 h and the average t½ for total phospholipids was about 20 h at 25 °C but nearly double that at 15 °C. However, phospholipids had a similar turnover rate in a soil with lower microbial biomass (84 mg C kg−1) compared to a soil with higher microbial biomass (305 mg C kg−1). Assimilation of 13C into other phospholipids was very low but followed the same timescale. Overall, this provides for the first time direct evidence for high turnover rates in soil through the analysis of specific 13C-labelled PLFAs and confirms the classic hypothesis that intact phospholipids represent living cells, necessary for the validity of the established PLFA methodology.

Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra: possible implications for Parkinson's disease

To determine whether increased oxidative stress in substantia nigra of patients with idiopathic Parkinson's disease might be related to decreased ability of nigral cells to detoxify oxidized membrane phospholipids, we compared levels of the major phospholipid metabolizing enzymes in autopsied substantia nigra with those in non-nigral ( n=11) brain areas of the normal human brain. Whereas most enzymes possessed a relatively homogeneous distribution, the activity of the major phospholipid catabolizing enzyme phospholipase A 2, assayed in the presence of calcium ions, varied amongst different regions, with substantia nigra possessing the lowest activity. Similarly, calcium-independent phospholipase A 2 activity, although possessing a relatively homogeneous regional distribution, was also low in the substantia nigra. This, coupled with low activity of phosphoethanolamine- and phosphocholine-cytidylyltransferases, major regulatory enzymes of phospholipid synthesis, in this brain region, suggest that the rate of phospholipid turnover is low in the substantia nigra. Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra might result in reduced ability to repair oxidative membrane damage, as may occur in Parkinson's disease.

In vivo turnover of phospholipids in rabbit erythrocytes

The rate of phospholipid turnover in erythrocyte membranes in vivo has been studied using a recently developed procedure (Kuypers F.A., Easton E.W., van den Hoven R., Wensing T., Roelofsen B., Op den Kamp J.A.F. and van Deenen L.L.M. (1985) Biochim. Biophys. Acta 819, 170–178). The technique is based on the application of phospholipid transfer proteins in order to introduce trace amounts of radiolabelled phospholipids in the membrane of isolated erythrocytes, followed by re-injection of the erythrocytes into the bloodstream of the animal. The most abundant species of the phosphatidylcholine (PC) class, l-palmitoyl,2-linoleoyl PC, has, on the basis of loss of the radioactivity in its fatty acyl part, a relatively high turnover with a half-time value of 1.5 days. Other PC species studied exhibit more moderate turnover rates of about 5 days for l-palmitoyl,2-oleoyl PC and l-stearoyl,2-arachidonoyl PC. Dipalmitoyl PC, labelled in the polar headgroup, turns over at a slow rate with a half-time value of 9 days. From these data and the relative abundance of the various species, it can be calculated that, on a daily basis in vivo, about one third of the total PC pool in rabbit erythrocyte membranes is replaced and/or modified by de-/reacylation. The only phosphatidylethanolamine (PE) species studied so far, 1-palmitoyl,2-arachidonoyl PE, appeared to be renewed at a relatively low rate with a half-time value of 12 days. The data demonstrate that the in vivo turnover values of phospholipids in the erythrocyte membrane may depend on their polar head group structure, their localization in the membrane and, to a large extent, on their fatty acid composition.

THE EFFECT OF LECTINS ON GERMINATING POLLEN OF LILIUM LONGIFLORUM II. EFFECT OF CONCANAVALIN A ON PHOSPHOLIPID TURNOVER AND ON BIOSYNTHESIS OF PECTIC POLYSACCHARIDES

SUMMARY The present study describes the effect of Concanavalin A (Con A, 200 μg/ml) on phospholipid turnover and on the biosynthesis of pectic polysaccharides in germinating pollen of Lilium longiflorum. Both phenomena are directly involved in pollen tube growth. The turnover rate of phospholipids was reduced with about 50% by the presence of Con A during the first 4 hours of germination. When Con A was added after 4 hours of incubation in the absence of lectin, a sudden shift of tritium label was observed from phospholipids to 1,2-diacylglycerol. This shift is probably due to inhibition of phospholipid synthesis during the turnover process, while degradation continues. The biosynthesis of pectic polysacharides was also inhibited with about 50% upon addition of Con A either at the onset of germination or to actively growing pollen tubes which were preincubated for 4 hours in the absence of lectin.

Investigation of phospholipid changes in actively metabolizing cells by high-performance liquid chromatoraphy of 32P-labelled phospholipids

A high-performance liquid chromatographic system was employed to study turnover rates of phospholipids in various types of cells, such as leukocytes, erythrocytes and yeast cells. In the extracts obtained from 32P-labelled cells ten to twelve different phospholipids could be identified. Phosphatidyl glycerol and other minor phospholipids show a high specific activity, so that the lipids may be readily detected. The reproducibility and sensitivity of the method permits the determination of lipid changes during nutrient uptake, phagocytosis, or other cellular activities.

Drug-induced phospholipidosis. II. Alterations in the phospholipid pattern of organs from mice, rats and guinea-pigs after chronic treatment with chlorphentermine.

In three species chronic treatment with the anorectic drug chlorphentermine causes a profound alteration of the phospholipid/lipid metabolism in the organism, resulting in an increase of the fractions of phospholipids and lipids, e.g. in lungs, livers and adrenals. The results are interpreted as drug-induced generalized phospholipidosis, which is caused by amphiphilic drugs, like chlorphentermine and others. Its extent depends on several factors, like content, pattern and turnover rate of phospholipids in different organs, and on the species.

An effect of ethylene on the endoplasmic reticulum of expanding cells of etiolated shoots of Pisum sativum L.

Within 6 h of supplying ethylene to intact etiolated seedlings of Pisum sativum L. increasingly long profiles of rough and smooth endoplasmic reticulum (ER) appear in sections of epidermal and cortical cells from the hook region. By 24 h some profiles exceed 10 μm in length, more than 10 times the length of the longest commonly observed in control tissue. These profiles are not artifacts of the different preparations, for similar extended profiles occur in sections of pellets of rough ER which have been prepared from subapical internodes of treated seedlings by extraction and separation of the membranes on sucrose gradients. It is proposed that the changes in rough ER result from a 'stabilisation' of the membranes brought about by a reduced rate of phospholipid turnover in the presence of ethylene.

Phospholipid synthesis in rat liver endoplasmic reticulum after the administration of phenobarbitone and 20-methylcholanthrene.

1. Phenobarbitone injection did not affect the concentration of phospholipids in the liver endoplasmic reticulum, but it increased the rate of incorporation of [(32)P]orthophosphate into the phospholipids. 20-Methylcholanthrene caused a transient increase in total phospholipid but a decrease in the turnover rate of the phospholipids. 2. Incorporation of [(32)P]orthophosphate into phosphatidylcholine, compared with that into phosphatidylethanolamine, was increased by phenobarbitone injection but decreased by 20-methylcholanthrene injection. 3. The activity of S-adenosylmethionine-phosphatidylethanolamine methyltransferase increased 12h after phenobarbitone injection, when incorporation of [(32)P]orthophosphate into phosphatidylcholine was a maximum, but at other times, and after 20-methylcholanthrene injection, the activity of the enzyme did not correlate with the rate of phosphatidylcholine synthesis. 4. [(14)C]Glycerol was incorporated more rapidly into phosphatidylcholine than into phosphatidylethanolamine, whereas [(32)P]orthophosphate and [(14)C]ethanolamine were incorporated more rapidly into phosphatidylethanolamine than into phosphatidylcholine. 5. Incorporation of [(32)P]orthophosphate into phosphatidylethanolamine of liver slices incubated in vitro was much more rapid than into phosphatidylcholine, and incorporation into phosphatidylcholine was markedly stimulated by addition of methionine to the medium. Changes in the incorporation of [(32)P]orthophosphate into phospholipids observed in vivo after injection of phenobarbitone or methylcholanthrene could not be reproduced in slices incubated in vitro. 6. It is concluded that phenobarbitone injection causes an increased rate of turnover of total phospholipids in the endoplasmic reticulum and an increased conversion of phosphatidylethanolamine into phosphatidylcholine, whereas 20-methylcholanthrene injection depresses both the turnover rate of total phospholipids and the formation of phosphatidylcholine.