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Biomedical subjects

D Rubinstein

Publications and source records attributed to D Rubinstein.

At least 73 records · Page 4Linked to original sources
PubMed1975

An incubation medium for the elevation of adenosine triphosphate and 2,3-diphosphoglycerate in fresh and long-preserved human erythrocytes.

The levels of adenosine triphosphate (ATP) and 2,3-diphosphoglycerate in freshly drawn human erythrocytes can be tripled by a 2 h incubation at 37 degrees C in a medium containing 21 mM glucose, 1.8 mM adenine, 5 mM pyruvate, 10 mM inosine, and 96 mM phosphate. Similar incubation conditions will restore the levels of ATP and 2,3-diphosphoglycerate in erythrocytes from blood levels preserved for 12 and 15 weeks, respectively, to those of fresh cells. Omission of pyruvate from the incubation medium further increases the level of ATP slightly, but there is little elevation of 2,3-diphosphoglycerate. Under these conditions labelled pyruvate and lactate production from [14-C]glucose or [14-C]inosine is not diminished, but labelled fructose 1,6-diphosphate, rather than 2,3-diphosphoglycerate, accumulates. In addition, omission of pyruvate from the incubation medium, with a concomitant decrease in accumulation of 2,3-diphosphoglycerate, diminishes the concentration of inorganic phosphate required for optimal ATP elevation. A 5 h incubation in the glucose-adenine-pyruvate-inosine-phosphate medium elevates the levels of ATP and 2,3-diphosphoglycerate in erythrocytes from blood preserved in the cold for 15 weeks to twice that of fresh cells, indicating that the cells retain their metabolic potential even after prolonged storage at 2 degrees C. The medium may provide a method of rejuvenating 10-12 week cold-preserved erythrocytes for transfusion purposes, by a 1 h incubation at 37 degrees C.

Adenine↗
PubMed1974

Secretion of apolipoproteins in very low density and high density lipoproteins by perfused rat liver.

The incorporation of labeled amino acids into the peptides of very low density lipoproteins (VLDL) and high density lipoproteins (HDL) secreted by perfused rat liver was studied using a Ringer-albumin solution in the perfusate in place of serum to diminish exchange of peptides between VLDL and HDL. Among the lipoproteins, the greatest release of protein, greatest incorporation of amino acid, and highest specific activity were found in VLDL. After separation of the delipidated peptides by electrophoresis on polyacrylamide gel, the incorporation into VLDL peptides was found to be 5-10 times as great as into HDL peptides. There was virtually no incorporation into the peptides of low density lipoproteins (LDL). Approximately 25% of the radioactivity incorporated into perfusate VLDL failed to enter the 13% polyacrylamide gel. The remaining radioactivity was distributed primarily among three peptide bands; one, found in the upper portion of the gel, contained 45% of the total, most of the remainder being found in two rapidly migrating bands. These three peptides appear to approximate those of human apo-C in relative electrophoretic mobility. Most of the HDL peptide radioactivity entering the running gel was found in a band that migrates slightly faster than the main VLDL band. A portion of the radioactivity of this major HDL band did not enter the running gel unless beta-mercaptoethanol was present. Greater separation of these two bands by polyacrylamide gel electrophoresis for 24 hr confirmed that the major bands in VLDL and in HDL were different. The rapidly moving peptides of HDL were found to contain very little radioactivity. Determination of the intensity of staining of carrier-free perfusate VLDL and HDL peptides produced a pattern similar to the incorporation of labeled amino acids. It is concluded that the rapidly moving peptides, which may contain activators of lipoprotein lipase, are only secreted as part of the VLDL.

Amino Acids↗
PubMed1973

Comparison of the metabolic behavior in vitro of the apoproteins of rat serum high density lipoprotein2 and high density lipoprotein3.

Rat serum high density lipoproteins were divided into two fractions, HDL(2) (d 1.063-1.12) and HDL(3) (d 1.12-1.21). These fractions were compared on the basis of (a) the pattern of the apolipoprotein peptides obtained on polyacrylamide gel electrophoresis in 7 m urea, (b) the exchange of some of the peptides with those in very low density lipoproteins (VLDL), and (c) the incorporation by perfused rat liver of [(3)H]leucine into the peptides of the HDL(2) and HDL(3) secreted into the perfusate. Among the peptide bands of HDL(3), one is absent and another present only in trace amounts in HDL(2). After electrophoresis on polyacrylamide gel for 24 hr, a major peptide band of HDL(2) is split into three distinct areas, whereas it remains as a single area in HDL(3). Both HDL(2) and HDL(3) exchange prelabeled protein with VLDL. However, the exchange is much more limited in HDL(3), even though it contains most of the protein found in circulating rat HDL. Analysis of the individual peptides, separated by polyacrylamide gel electrophoresis after incubation with VLDL, reveals that in HDL(3) the exchange is limited to two peptides, whereas a third, although present in both subfractions of rat HDL, exchanges only when found in HDL(2). This peptide represents most of the exchange with VLDL. Perfused rat liver incorporates [(3)H]leucine into HDL of the perfusate, primarily into HDL(2). Most of the radioactivity is found in those peptides that do not take part in the exchange with VLDL. These data lead to the conclusions that there are functional and structural differences between HDL(2) and HDL(3) and that some of the peptides of HDL may be derived from exchange with, and breakdown of, VLDL. Others are secreted, at least in part, directly into the circulation by the liver.

Animals↗
PubMed1972

Interrelationship between rat serum very low density and high density lipoproteins.

An exchange of phospholipids and certain peptides among various classes of rat serum lipoproteins has been demonstrated and its nature has been investigated. [(32)P]-Phospholipid from isolated VLDL, prepared in vivo, was transferred to HDL, and to a much lesser extent to LDL, in vivo and in vitro. This difference between HDL and LDL can be abolished by ultracentrifugation of the serum at d 1.21. Unlabeled VLDL acquired [(32)P]phospholipid from HDL of serum. Phospholipid associated with the alpha-lipoprotein component of VLDL exchanged more readily than that associated with the beta-lipoprotein component of VLDL. Generally, the phospholipid species exchange in proportion to their distribution in the lipoproteins. Radioactivity from (3)H-labeled protein of VLDL was transferred to HDL while HDL (3)H-labeled protein in serum was transferred to VLDL during a 20-min incubation. LDL was not involved in the transfer of protein. Protein associated with the alpha-lipoprotein component of VLDL exchanged more readily than that associated with beta-lipoprotein component. Analysis of tritiated apoproteins of VLDL and HDL by polyacrylamide gel electrophoresis revealed that three of the six peptide bands of apo-VLDL exchanged between VLDL and HDL. The data raise the possibility that intact subunits of the VLDL and HDL are being exchanged.

Amino Acids↗