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Biomedical subjects

M Waite

Publications and source records attributed to M Waite.

At least 91 records · Page 5Linked to original sources
PubMed1980

The effect of mouse serum on lipid metabolism in embryonic chick limb-bud cells.

Dissociated embryonic chick limb cells will undergo terminal differentiation in culture. The addition of whole or delipidated mouse serum to the cultures will, however, inhibit the chondrogenic potential of the cells. The inhibitory serum readily stimulates increased incorporation of arachidonic acid and palmitic acid into triacylglycerol in the treated cells, while the incorporation of arachidonate into various phospholipids is significantly lowered. In contrast mouse serum has no effect on the incorporation of inorganic [32P]phosphate into phospholipid. We interpret the patterns of incorporation of these lipid substrates as indicating that mouse serum modulates the deacylation-reacylation cycle of phospholipids (Lands' cycle), which is primarily responsible for the incorporation of arachidonic acid. This finding suggests that there may be a decrease in membrane fluidity which might play a key role in cellular regulation and differentiation.

Animals↗
PubMed1979

Metabolism of lipoprotein acylglycerols by liver parenchymal cells.

We investigated the metabolism by hepatocyte suspensions of the acylglycerols in lipoprotein remnants as well as those associated with albumin and low or high density lipoproteins. Remnants, albumin and plasma lipoproteins, rich in monoacylglycerol were prepared by short-term incubations of radio-labeled chylomicra or very low density lipoproteins with extrahepatic lipoprotein lipase in the presence of albumin and low and high density lipoproteins. We demonstrated that liver parenchymal cells contain an active monoacylglycerol acyltransferase that is located on the extracellular surface of the cell plasma membrane. Further, the enzyme is capable of degrading the monoacylglycerol in all the above forms. Triacylglycerol in intact chylomicra and very low density lipoproteins were not metabolized by the cells to any appreciable degree. The degradation of the remnant triacylglycerol appeared to depend solely on the activity of the lipoprotein lipase bound to the lipoprotein remnants. Little uptake of intact lipoprotein acylglycerols by the hepatocytes was observed; instead, hydrolysis of the substrates in the medium always preceded the uptake of the products. The products were then utilized for the synthesis of triacylglycerol and phospholipid within the cells.

Animals↗
PubMed1978

A comparison of the lipolytic activities in liver perfusates and liver plasma membranes from rats.

We have undertaken a study to resolve the conflicting reports on the substrate specificity of the lipolytic enzyme(s) released by heparin from liver and report the following: (1) Heparin perfusates from liver contain an enzyme(s) capable of degrading triacylglycerol, diacylglycerophosphorylethanolamine and monoacylglycerol, whereas a heparin-solubilized fraction from liver plasma membranes hydrolyzes diacylglycerophosphorylethanolamine and monoacylglycerol only; (2) The lipolytic activities for the two sources behave differently on gel filtration but have the same behavior on heparin-Sepharose affinity chromatography; (3) Treatment of the preparation from the plasma membrane with Triton X-100 followed by heparin-Sepharose affinity chromatography produces forms of the enzyme(s) that now have activity on triacylglycerol This study suggests that the enzyme(s) from the two sources may be the same and that some change occurs when the enzyme is released from the intact liver.

Acyltransferases↗
PubMed1978

Disintegration of phosphatidylcholine liposomes in plasma as a result of interaction with high-density lipoproteins.

1. During in vitro incubation of liposomes or unilamellar vesicles prepared from egg-yolk or rat-liver phosphatidylcholine with human, monkey or rat plasma the phospholipid becomes associated with a high molecular weight protein-containing component. 2. The phosphatidylcholine . protein complex thus formed co-chromatographs with high-density lipoprotein on Ultrogel AcA34 and has the same immunoelectrophoretic properties as this lipoprotein. 3. Release of the phosphatidylcholine from liposomes was also observed when liposomes were incubated with pure monkey high-density lipoproteins. Under those conditions some transfer of protein from the lipoprotein to the liposomes was observed as well. 4. The observed release of phospholipid from the liposomes is a one-way process, as the specific radioactivity of liposome-associated phosphatidylcholine remained constant during incubation with plasma. 5. It is concluded that either the lipoprotein particle takes up additional phospholipid or that a new complex is formed from protein constituents of the lipoprotein and the liposomal phosphatidylcholine. 6. Massive release of entrapped 125I-labeled albumin from the liposome during incubation with plasma suggests that the observed release of phosphatidylcholine from the liposomes has a highly destructive influence on the liposomal structure. 7. Our results are discussed with special reference to the use of liposomes as intravenous carriers of drugs and enzymes.

Animals↗
PubMed1978

Mitochondrial phospholipase A2 activity and mitochondrial aging.

The changes in mitochondrial phospholipid metabolism and energy-linked functions have been followed as coupled mitochondria are allowed to age in isotonic sucrose at 18 degrees C. Analysis of the aging process has provided an approach for studying the structure--function relationships within the mitochondrion without adding external agents to perturb the membrane structure. The initial event observed in this process of deterioration is a loss of respiratory control which is paralleled by diminishing levels of ATP. As ATP levels decline, so do the rates of reacylation of monoacyglycerophosphorylethanolamine and fatty acid oxidation. In most cases the previously inactive phospholipase A2 (EC 3.1.1.4, phosphatide-2-acyl-hydrolase) begins rapid hydrolysis of membrane phosphatidylethanolamine as ATP levels approach zero. The final energy-linked phenomenon observed to decline is the anilinonaphthalenesulfonic acid fluorescence response. Evidence is presented which suggests strongly that the activity of the mitochondrial phospholipase A2 on endogenous phospholipids is suppressed in tightly coupled mitochondria. This suppression is temporally linked to ATP levels in the mitochondria. Furthermore, this study demonstrates that mitochondria which are only slightly damaged have the potential to effect membrane repair through reacylation of monoacyl phospholipids.

Adenosine Triphosphate↗
PubMed1977

Membrane lipid metabolism of Bacillus Calmette-Guerin-induced rabbit alveolar macrophages.

We examined the uptake of radiolabeled lysophospholipids and oleic acid by Bacillus Calmette-Guerin-induced rabbit alveolar macrophages either in the presence or absence of challenge particles. There was no difference in the uptake and metabolism of lysophospholipids by control or challenged cells for incubation periods up to 5 h. When incubated with [3H]oleic acid, challenged cells consistently exhibited a slightly greater uptake of radioactivity. Extraction of the whole cells revealed that the greater amount of radioactivity found in the challenged cells primarily was in triacylglycerol. There was no marked difference in the amount of radioactivity associated with the phospholipids in the whole cell extracts from control and challenged cells. When the macrophages were pre-labeled for 15 min with [3H]oleic acid and then reincubated in fresh medium in the presence or absence of autoclaved Escherichia coli B, more radioactivity was retained by the challenged cells, again in the form of triacylglycerol. Only in isolated plasma membrane fractions did we observe a difference in the amount of radioactivity associated with phospholipids from control and challenged cells. Plasma membranes isolated from Bacillus Calmette-Guerin-induced rabbit alveolar macrophages that had been incubated for 6 h with [3]oleic acid in the presence of E. coli B contained significantly higher level of radioactivity in all lipids than plasma membranes from control cells. Since the greatest and the most consistent difference between control and challenged cells is associated with the triacylglycerol molecule, it is postulated that this molecule may serve as a precursor in the synthesis of alveolar macrophage phospholipids, both by the reacylation pathway and the de novo pathway. It is possible that the high level of radiolabeled phospholipid found in the plasma membrane arose via the de novo pathway following the cleavage of an acyl group as we have found cytidine diphosphocholine phosphotransferase in the plasma membrane fraction (Wang, P., DeChatelet, L.R., and Waite, M. (1977) Biochim. Biophys. Acta 450, 311--321).

Animals↗
PubMed1977

Lipid synthesis in cultured human embryonic fibroblasts.

We describe here the pathways by which human embryonic fibroblasts synthesize lipids. In these studies, we quantitated the phospholipds by their phosphorus content and by their acyl components. These determinations defined both the chemical composition of the cellular membranes as well as their metabolic turnover. Using radiolabeled precursors, we have shown (a) synthesis of the glycerol moiety via glycolysis and the action of glycerokinase, (b) utilization of both exogenously added and endogenously synthesized fatty acids, (c) synthesis de novo of phosphatidyl choline and phsphatidyl ethanolamine from their base precursors, and (d) the methylation of phosphatidyl ethanolamine yielding phosphatidyl choline. Dividing cells synthesized phosphoglyceride more rapidly than cells in the stationary phase. However, considerable turnover of cellular lipid did occur in the stationary phase.

Acetates↗
PubMed1976

Utilization of serum lipoprotein lipids by the monoacylglycerol acyltransferase.

The plasma membrane of rat liver contains an enzyme which is stimulated by heparin and hydrolyzes liposomes composed of phosphoglycerides as well as mono-and diacylglycerol (Waite, M. and Sisson, P (1973) J.Biol, Chem. 248, 7985-7902). Further, in liposomes this enzyme catalyzes a transacylation in which the acyl group is removed from position 1 of an acyl glyceride donor, and combined with the hydroxy group of a variety of acyl acceptors. To investigate the possible role of this enzyme in lipoprotein metabolism, we have incorporated specific labeled glycerides into lipoproteins. The high density, low and very low lipoproteins were then separated by molecular sieving and characterized by their physical and chemical properties. Using the labeled substrates as model lipoproteins, we found the following: 1)The enzyme is capable of hydrolyzing monoacylglycerol, diacylglycerophosphoethanolamine and diacylglycerophosphocholine; monoacylglycerol however is the preferred substrate in all three lipoprotein fractions. 2)Relative to the activity found on liposomes, the transacylation activity is low. 3)The specific radioactivity of the substrates in fraction B (low density lipoprotein) did not change during the reaction, which indicates that the labeled lipid is not a pool separate from the endogenous lipid of the lipoprotein.

Acyltransferases↗
PubMed1976

Enzymes of phospholipid synthesis in Bacillus Calmette-Guerin induced rabbit alveolar macrophage. Characterization and localization of cytidine diphosphocholine phosphotransferase and monoacylphospholipid acyltransferase.

The rabbit alveolar macrophage is capable of renewing its plasma membrane by at least two metabolic pathways. It contains (1) a monoacylphospholipid acyltransferase, which catalyzes the synthesis of diacylphospholipids by recycling monoacylphospholipids produced by the action of phospholipases and (2) a cytidine diphosphocholine phosphotransferase (CDPcholine phosphotransferase), which catalyzes the last step in the synthesis de novo of diacylglycerophosphocholine. These activities have been characterized in the cell homogenate with respect to time, protein, pH optimum (for CDPcholine phosphotransferase), substrate specificity (for monoacylphospholipid acyltransferase) and cation requirement ( for CDPcholine phosphotransferase). Monoacylphospholipid acyltransferase activity is localized solely in the endoplasmic reticulum. On the other hand, the CDPcholine phosphotransferase activity can be measured in the endoplasmic reticulum and in the plasma membrane, characterized by both differential and gradient sedimentation techniques. In addition to the normal route of phospholipid synthesis in the endoplasmic reticulum, the rabbit alveolar macrophage may thus possess the capacity for in situ synthesis of phospholipids of plasma membrane as a mechanism for membrane renewal following phagocytosis.

Acyltransferases↗