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Biomedical subjects

A A Spector

Publications and source records attributed to A A Spector.

At least 235 records · Page 13Linked to original sources
PubMed1970

Utilization of long-chain free fatty acids by human platelets.

There was a rapid net uptake of free fatty acid (FFA) by human platelets when long-chain FFA, bound to human serum albumin, were incubated with platelet suspensions. Results from experiments in which both palmitate and albumin were labeled indicated that the fatty acid dissociated from the protein during uptake. Much of the FFA taken up by the platelet in short-term incubations remained in unesterified form, i.e., it was recovered as platelet FFA. As the incubation continued, increasing amounts of FFA were oxidized to CO(2) and incorporated into platelet lipid esters, particularly lecithin. Essentially all of the fatty acid that was incorporated into the platelet FFA fraction was released rapidly from the cells when they were exposed to a medium containing FFA-free albumin. The magnitude of uptake into the platelet FFA fraction was similiar at 0 degrees and 37 degrees C. Likewise, the rate and magnitude of FFA release from the platelet were similar at 0 degrees and 37 degrees C. Therefore, it is likely that both FFA uptake and FFA release occur by energy-independent mechanisms. The major effect of increasing the FFA concentration of the incubation medium was increased fatty acid uptake into the platelet FFA fraction. Similar results occurred when platelets were incubated in human plasma containing increasing amounts of added palmitate. At a given extracellular FFA concentration, considerably more of the saturated fatty acids, palmitate and stearate, were taken up as platelet FFA than either oleate or linoleate.

Blood Platelets↗
PubMed1970

Uptake of long-chain fatty acid methyl esters by mammalian cells.

Albumin-bound long-chain fatty acid methyl esters (ME) were taken up and utilized by Ehrlich ascites tumor cells and slices of rat heart, liver, and kidney. Much more ME than albumin was taken up by the tumor cells, indicating that ME dissociated from the carrier protein during their uptake. 70-80% of the radioactivity associated with the cells after 1 min of incubation at 37 degrees C remained as ME. The results of studies with metabolic inhibitors and glucose suggest that uptake of ME is an energy-independent process. Changes in incubation medium pH between 7.8 and 6.5 did not markedly alter uptake of ME. Cells incubated with FFA and methanol did not synthesize ME. These findings indicate that ME are taken up intact, and they suggest that the presence of an anionic carboxyl group is not essential for the binding of a long-chain aliphatic hydrocarbon to a mammalian cell. When incubation with labeled ME was continued for 1 hr, increasing amounts of radioactivity were recovered in FFA, phospholipids, neutral lipid esters, and CO(2). ME radioactivity associated with the cells after a brief initial incubation was released in the form of ME and FFA when the cells were incubated subsequently in a medium containing albumin. If the second incubation medium contained no albumin, most of the ME radioactivity initially associated with the cells was incorporated into phospholipids, neutral lipid esters, and CO(2). These results suggest that much of the ME which is taken up, is hydrolyzed to FFA, and that the fatty acids derived from ME are available for further metabolism.

Albumins↗
PubMed1969

Binding of long-chain fatty acids to bovine serum albumin.

We have studied the binding of long-chain free fatty acids (FFA) to crystalline bovine serum albumin (BSA) that had been extracted with charcoal to remove endogenous fatty acids. The data were analyzed in terms of a model consisting of six high-energy binding sites and a large number of weak binding sites. The high-energy sites were resolved into two distinct classes, each containing three sites. At 37 degrees C and pH 7.4, k'(1) (the apparent association constant of a class of binding sites) was about 10(6) m(-1) for binding to the three primary sites, and k'(2) was about 10(5) m(-1) for binding to the three secondary sites. The number of weak (tertiary) sites was estimated to be 63 with a k'(3) of 10(3) m(-1). In general, palmitate and palmitoleate were bound more tightly than oleate, linoleate, stearate, or myristate, and much more tightly than laurate. The association of palmitate with human and rabbit albumin also was analyzed in terms of this model. Palmitate was bound less firmly by human or rabbit albumin than by BSA. Palmitate binding to BSA was dependent upon the pH and temperature of the incubation medium. Long-chain hydrocarbons that did not contain a free carboxyl group (methyl palmitate, cetyl alcohol, and hexadecane) were bound to a limited extent and weakly. The presence of positively charged protein sites and native protein tertiary structure were required for maximal binding of palmitate to BSA. Of nine other proteins tested, only -lactoglobulin exhibited a significant capacity to bind palmitate.

Animals↗
PubMed1969

Influence of pH of the medium on free fatty acid utilization by isolated mammalian cells.

Studies with Ehrlich ascites tumor cells showed that small decreases in the pH of the incubation medium from 7.4 increase the magnitude of incorporation of free fatty acid (FFA) into the cells from an albumin solution. A similar effect occurred when rabbit erythrocytes, rat heart slices, or rat liver slices were incubated with FFA-bovine albumin solutions and when tumor cells were incubated with FFA in media containing human albumin, -lactoglobulin, or rat plasma. The effect was not seen when the medium contained no protein. When the pH of the albumin-containing medium was lowered from 7.4 to 6.6, oxidation of FFA to CO(2) by the tumor cells increased, esterification of the FFA (mostly into phospholipids and triglycerides) increased, and less esterified radio-active fatty acid was depleted from the cells. Hence, more fatty acid accumulated in the cells in more acid media. These findings suggest that small changes in extracellular pH might regulate FFA utilization and lipid accumulation in mammalian tissues.

Albumins↗
PubMed1966

Release of free fatty acids from Ehrlich ascites tumor cells.

Ehrlich ascites tumor cells release free fatty acids (FFA) during in vitro incubation in media that contain albumin. The released FFA are derived by lipolysis from endogenous lipid esters. Addition of glucose to the incubation medium greatly decreases the quantity of fatty acid released by the cells. Cyanide, which inhibits endogenous lipid oxidation but not lipolysis, increases the quantity of fatty acid released to media containing albumin and causes free fatty acid to accumulate in the cells in the absence of exogenous albumin. The release of fatty acid, either preformed or derived by lipolysis during prolonged incubations, occurs under conditions of net fatty acid uptake from the incubation medium. Net release of fatty acid from the cell occurs only when fatty acid-extracted albumin is present in the extracellular medium; extrapolation of the data suggests that net release will not occur under physiological conditions. It is postulated that free fatty acid uptake and release are independent processes, the direction of net fatty acid movement being determined by the relationship between cellular free fatty acid concentration (regulating efflux) and the molar ratio of free fatty acid to albumin in the extracellular medium (regulating uptake).

Animals↗