Bertram A. Lowy

The Effects of Nucleosides On the Resistance of Normal Human Erythrocytes to Osmotic lysis

The investigations reported in this paper proceeded on the hypothesis that maintenance of the structural integrity of the human erythrocyte is dependent on continued production and utilization of energy by the cell. In an attempt to test this hypothesis the susceptibility of fresh human erythrocytes to osmotic lysis was studied in terms of the influence of various compounds that might serve as substrates for energy yielding reactions within the erythrocyte. Particular attention was paid to glucose (3) and purine nucleosides (4, 7) which have been shown to prolong the viability of stored erythrocytes and to retard their progressive lysis and diminished resistance to hypotonic solutions. It may be noted, however, that the effectiveness of the purine nucleosides in the preservation of erythrocytes has recently been questioned (8).

A Role of Liver Adenosine in the Renewal of the Adenine Nucleotides of Human and Rabbit Erythrocytes

For many years the work of our laboratory has been concerned with the synthesis and metabolism of the purine nucleotides in the mature human and rabbit erythrocyte and in the rabbit reticulocyte. Our early studies (1–5) and those of Mager’s group (6,7) and others (8) have demonstrated the metabolic renewal of the purine nucleotides within the circulating erythrocyte during its lifespan. The observed turnover occurs in the absence of the capacity for the de novo biosynthetic pathway in the erythrocytes of both species, although the cells do contain purine nucleoside phosphorylase as well as adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase. However, the human erythrocyte lacks adenylosuccinate synthetase (9) and thus is unable to convert IMP to AMP, an enzymatic capacity possessed by the rabbit red cell. The erythrocytes of both species do possess adenylosuccinase and can, therefore, convert adenylosuccinate to AMP, and succinylaminoimidazolecarboxamide ribotide to aminoimidazolecarboxamide ribotide (AICAR). Formylation of AICAR and ring closure, which can occur in the erythrocyte, then leads to IMP formation. We had reported some years ago that the loss of a portion of the de novo pathway accompanies the maturation of the rabbit reticulocyte (4). More recent studies have indicated that many of the enzymes required for the early steps of the pathway are lacking in the erythrocytes of both species (10).

A STUDY OF THE SYNTHESIS AND INTERRELATIONSHIPS OF RIBONUCLEIC ACIDS IN DUCK ERYTHROCYTES.

Abstract Duck erythrocytes have served as a source for a number of RNA fractions. In addition to ribosomal and soluble RNA, five RNA fractions have been prepared from a 15 000 ×g residue, containing nuclei and cell membranes. Three of the fractions, constituting about 10 % of the total cellular RNA, exhibited a rapid uptake of labeled precursors. Studies to evaluate the possible role of the rapidly labeled fractions as cytoplasmic RNA precursors by chase and actinomycin-inhibition experiments suggest that a simple nuclear to cytoplasmic relationship may not exist in the duck erythrocyte.

Adenosine triphosphate metabolism in the rabbit erythrocyte in vivo and in vitro.

The mechanism associated with the control of the life span of the mammalian erythrocyte in zlivn presents a problem of major biological interest. Although little is known concerning the sequence of events leading to the destruction of the erythrocyte a t the end of a predictable period of time, it is probable that the initiating mechanism resides within the cell itself.2 ii s h d y of the erythrocyte with respect to certain constituents the concentrations of which may change during the aging process in cico may provide a clue to the process by which the destruction of the erythroLyte is initiated. The energy metabolism of the erythrocyte is primarily dependent upon the utilisation of glucose that enters the cell from the plasma by way of an active transport mechanism and is converted to glucose-6-phosphate. This reaction is catalyzed by hexokinase and requires adenosine triphosphate (ATP) a? a specific coenzyme. The subsequent metabolism of the glucose-6-phosphate provides a major source of energy for the maintenance of the cell. I n addition to serving as a specific coenzyme for many metabolic reactions, it is also a precurwr of a number of coenzymes and a mediator of energy transfer. During the aging of the erythrocyte in v i h o it is well knohn that the level of ATP declines progressively with a concomitant 1055 of viability of the itored erythrocyte.? A relationship of thii l o b \ of viability to the ATP level of the erythrocyte i5 implied by the finding that storage in media that maintain the ATP content for longer periods of time also results in a prolongation of the viability of the e r y t h r ~ c y t e . ~ Although ATP is multifunctional, the maintenance of the erythrocyte is probably related to the optimal functioning of the hevokinase reaction. The rapid turnover of the high-energy terminal phosphate groups of ATP in the erythrocyte has been s tu~ l i ed .~ However, a limiting factor for ATP lormation may be a diminished content of receptor molecules, that iq, adenosine monophosphate (AAlP) or adenosine diphosphate (ADP), for the attachment of one or more terminal phosphate groupi. Thii, in turn, will relate to the capacity of the circulating erythrocyte for replacement of losses of adenine nucleotides that may occur within the individual erythrocyte during the aging proceis. Jgrgensen has reported that iuch loises occur during aging iiz zlirro with the accumulation of free pur An investigation of the biosynt and metabolism of 4TP in the mature

An alternate metabolic route for the synthesis of inosine 5'-phosphate (IMP) in the Lesch-Nyhan erythrocyte.

The cells of the Lesch-Nyhan individual, which are deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity, lack the ability to convert the 6-keto purines, hypoxanthine and guanine, to the corresponding nucleotides (1). Mammalian cells, in general, lack appreciable kinase activity for the 6-keto purine nucleosides, inosine and guanosine (2,3). Thus, the major route to IMP and GMP in the Lesch- Nyhan cell is via the overall pathway of de novo purine nucleotide synthesis in which the purine ring of IMP is built up on carbon 1 of a molecule of ribose 5-phosphate (4), The IMP is readily converted to GMP in normal human and Lesch-Nyhan cells.