The effect of vincristine on haemoglobin synthesis

Vincristine in a concentration of 0.5 and 4 X 10--(5) M causes a decrease of 16% and 73% respectively, in the synthesis of globin by peripheral blood reticulocytes. At the higher drug concentration alpha/beta ratio is significantly lower than the normal ratio of unity and is 0.83 +/- 0.09. These effects of vincristine are probably related to the ability of the vinca alkaloids to bind to ribosomes and their subunits.

A family with red cell pyrimidine 5'-nucleotidase deficiency

Congenital hemolytic anemia associated with pyrimidine 5'-nucleotidase deficiency is reported in two siblings. Both have had moderate chronic hemolytic anemia, splenomegaly, and jaundice since early infancy. The peripheral blood smear is characterized by striking red cell basophilic stippling. As this feature has been found in all previously reported cases, it should be the clue to the diagnosis.

Complement-sensitive red cells in aplastic anemia

In view of the clinical association of aplastic anemia (AA) and paroxysmal nocturnal hemoglobinuria (PNH), the complement-dependent lysis of the youngest red cells of AA patients was studied. A complement-sensitive population of young red cells was found in five of six patients with AA. These cells were rapidly cleared from the circulation and were undetectable in the oldest cell fraction. Such cells were not found in normal controls or in a variety of hematologic disorders, with the exception of PNH. This study suggests that in most patients with AA, even without any clinical manifestations of PNH, there is a population of dyserythropoietic, short-lived complement-sensitive cells.

Characterization of erythrocyte membrane-associated enzymes (glyceraldehyde-3-phosphate dehydrogenase and phosphoglyceric kinase)

The purpose of our study was to determine why several of the glycolytic enzymes of the erythrocyte have the propensity for adhering to erythrocyte membranes while others do not. Two of these membrane-associated enzymes, glyceraldehyde phosphate dehydrogenase (GAPD) and phosphoglyceric kinase (PGK), have been shown to have controlling functions on intra-erythrocytic glycolysis and sodium-potassium transport. In order to test the hypothesis that the membrane-associated fraction of these enzymes consisted of isozymes with increased capacity to become membrane associated, the enzymes from cytosol or membrane sources were partially purified and characterized. Determination of molecular weight by gel filtration chromatography, measurement of certain kinetic parameters, and the curves relating to pH optimal activity indicated that there were no measurable differences between membrane and cytosol PGK and membrane and cytosol GAPD. It was possible to raise inhibitory antibodies to GAPD in certain species of mice, and these antibodies did not distinguish between GAPD isolated from either membrane or cytosol sources. GAPD was firmly bound to membranes and the membrane-associated fraction counted for approximately 60 per cent of total erythrocytic enzyme. Membrane-associated PGK was only loosely adherent, and accounted for only 1 per cent of the total erythrocytic enzyme. The reasons for membrane association have yet to be determined, but these inward facing membrane-associated enzymes appear to function by carrying the organization of the membrane into the cell interior.

Drug-induced erythrocyte membrane internalization

In vitro erythrocyte membrane internalization, resulting in the formation of membrane-lined vacuoles, can be quantified by a radioisotopic method. A complex of (37)Co-labeled vitamin B(12) and its plasma protein binders is first adsorbed to the cell surface, and after vacuoles are formed, the noninternalized label is removed by washing and trypsin treatment. The residual radioactivity represents trapped label and can be used to measure the extent of membrane internalization. Using this method, it was found that in addition to primaquine, a group of membrane-active drugs, specifically hydrocortisone, vinblastine, and chlorpromazine can induce membrane internalization in erythrocytes. This is a metabolic process dependent on drug concentration, temperature, and pH. Vacuole formation by all agents tested can be blocked by prior depletion of endogenous substrates or by poisoning the erythrocytes with sodium fluoride and sulfhydryl blocking agents. This phenomenon resembles in some respects the previously reported membrane internalization of energized erythrocyte ghosts. It is suggested that membrane internalization is dependent on an ATP-energized state and is influenced by the balance between the concentrations of magnesium and calcium in the membrane. This study provides a basis for proposing a unifying concept of the action of some membrane-active drugs, and for considering the role of erythrocyte membrane internalization in pathophysiologic events.

Physical characteristics of nonimmunologic adherence of IgG to RBC ghost membranes

These studies were undertaken with the aim of detecting possible differences between immunologic binding of IgG antibodies to erythrocyte membranes and the well documented nonimmunologic adherence to erythrocytes of large numbers of IgG molecules. In the experiments described D⁺(Rho) erythrocyte ghosts were incubated with either ¹²⁵I labelled anti-D or ¹²⁵I IgG and then thoroughly washed. The ghosts which contained either immunologically bound anti-D or adherent IgG were then passed through a French press which converted the ghosts into microvesicles composed of membrane material. This procedure resulted in the selective removal of nonimmunologically adherent IgG from the microvesicles while leaving most of the antibody still firmly bound to the microvesicles. A series of control studies revealed that this observation was not limited to a single preparation of anti-D or IgG, and was not related to the number of IgG molecules attached to the erythrocyte membrane. Selective methods of chemical elution did not distinguish between the two forms of IgG attachment nor did another physical manipulation i.e. freezing and thawing. Separation of the sheared microvesicles into distinct classes indicated that antibody binding and nonimmunologic adherence of IgG molecules occurred equally to each of the different vesicle classes. These observations indicated that antibody binding and nonimmunologic adherence of IgG differ with regard to their physical characteristics and this difference may be a reflection of the inability of nonimmunologically adherent molecules to react with the Coombs' reagent.