Red Cell Enzyme Activities Research Articles

Erythrocyte acetylcholinesterase and glucose-6-phosphate dehydrogenase in newborn infants of low birth weight

Red cell acetylcholinesterase (EC 3.1.1.7) activity is subnormal in ABO hemolytic disease of the newborn. Since this disorder also occurs in infants of low birth weight and inasmuch as the specific activity of several red cell enzymes is lower in these infants than in fullterm babies, acetylcholinesterase activity was determined within the second day of life in 120 newborn infants of low birth weight. Enzyme activity was lower in these infants than in normal full-term newborns, but significantly higher than in infants affected with ABO hemolytic disease of the newborn. The measurement of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), a sexlinked enzyme of importance in drug-induced hemolytic anemias and implicated in neonatal jaundice in certain populations, showed no differences in activity between infants of low birth weight and full-term infants.

The effect of copper on red cell enzyme activities.

Previous studies have shown a marked effect of very high levels of copper on red cell glucose-6-phosphate dehydrogenase and glutathione. When the effect of more nearly physiological levels of copper were studied, red cell hexokinase, phosphofructokinase, phosphoglyceric kinase, pyruvate kinase, and 6-phosphogluconate dehydrogenase were found to be inhibited. Inhibition was observed both when copper was added directly to hemolysates or when hemolysates were prepared from red cells from whole blood which had been incubated with copper and washed. The inhibition of red cell enzymes by copper was completely reversed by the addition of EDTA.

The effect of normal red cell constituents on the activities of red cell enzymes

The effect of 2,3-DPG, pyridoxal-5′- P, pyridoxal, pyridoxine creatine and bicarbonate was studied on the activity of red cell glycolytic and pentose phosphate shunt enzymes at saturating and limiting substrate concentrations. 2,3-DPG strongly inhibits the activity of hexokinase, phosphoglucomutase, phosphofructokinase, aldolase and glyceraldehyde phosphate dehydrogenase. In the case of the first four enzymes, 2,3-DPG competes with the substrate and glyceraldehyde phosphate dehydrogenase is inhibited in a noncompetitive fashion. Pyridoxal-5′- P inhibits some of the enzymes inhibited by 2,3-DPG, including hexokinase, phosphoglucomutase, phosphofructokinase and aldolase; in addition, it also inhibits the activity of phosphoglucose isomerase, pyruvate kinase, glucose-6- P dehydrogenase and 6-phosphogluconate dehydrogenase. In some cases, the inhibition was competitive; in others, it was noncompetitive. Creatine and bicarbonate do not significantly inhibit any of the enzymes studied. The studies reported in this report indicate possible roles of 2,3-DPG and pyridoxal-5′- P in the regulation of glucose metabolism in red cells.

Liver galactose-1-phosphate uridyl transferase: activity in normal and galactosemic subjects.

The kinetic characteristics of galactose-l-phosphate uridyl transferase have been determined in homogenates of human liver biopsies obtained from control subjects and in 50-fold purified enzyme preparations from liver obtained at autopsy. A standardized assay procedure employing linear kinetics was used to assess the enzyme activity in homogenates of liver biopsy specimens from five control subjects and four patients with congential galactosemia with demonstrated absence of the enzyme activity in red blood cells. Activity of control specimens ranged from 11.8 to 17.2 mmumoles of UDPgalactose formed per min mg of protein. Liver of two galactosemic patients, both Caucasian, possessed no detectable enzyme activity (less than 1-2% of normal). The tissue of two others, both Negro, who are known to be capable of metabolizing intravenously administered galactose, contained easily detectable enzyme at approximately 10% of the controls. No alternate enzymatic activity for formation of UDPgalactose was found in the liver of Negroes with galactosemia that was as active as the residual galactose-l-phosphate uridyl transferase. The data suggest that the residual liver enzyme activity accounts for the ability of Negroes with galactosemia to metabolize limited but significantly large quantities of galactose.

A Philippino Glucose-6-Phosphate Dehydrogenase Variant (G6PD Union) With Enzyme Deficiency and Altered Substrate Specificity

Abstract A variant of glucose-6-phosphate dehydrogenase (G6PD) associated with altered substrate specificity and severe deficiency of red cell enzyme activity was found in a Philippino male and in his relatives. The genetic pattern was consistent with X-linked inheritance. α-Thalassemia was found in the propositus and in several family members, but there was no interaction between G6PD deficiency and α-thalassemia. This G6PD variant has two pH optima, at pH 5.5 and pH 9.0, while the normal enzyme is inactive at pH 5.5. The substrate specificity of the variant enzyme is different from any known G6PD variant: 2-deoxyglucose-6-phosphate and galactose-6-phosphate are good substrates and deamino-NADP is a better coenzyme than NADP. Although G6PD activity in the variant red cells was only three per cent of normal, quantitative immunologic neutralization suggested that the specific activity of the variant enzyme might be at least ten per cent of that of the normal enzyme. This variant is named after the place of origin, Gd Union.

The uptake of plasma fatty acids into human red cells and its relationship to cell age

The uptake of labelled linoleate and palmitate from plasma into human red cells and red cell ghosts has been investigated, after fractionation of the cells according to age, by ultracentrifugation over a discontinuous density gradient of isotonic albumin solutions. Uptake into phosphatidylcholine, phosphatidylethanolamine, components identified as phosphatidic acid and diglyceride, and an unidentified nonpolar lipid have been observed. Both total fatty acid uptake, and the distribution of the incorporated acid in the cell lipids, varied considerably for different normal populations of red cells. It is suggested that variations in plasma concentrations of the substrates for the incorporation reactions could have been the cause of the diverse behaviour. No clear-cut relationship between red cell age and the rate of uptake of plasma fatty acids was apparent. In some cases, uptake into all lipid components was essentially constant, but in others, uptakes into specific components showed definite trends with age. Most noteworthy were either a marked increase in uptake into phosphatidylethanolamine, or a decrease in uptake into phosphatidylcholine. To account for these findings, it is postulated that activities of the relevant red cell enzymes are age-dependent, but that the differences between young and old cells are only evident under some plasma conditions.

In vitro hybridization of normal and variant human glucose-6-phosphate dehydrogenase.

NORMAL human glucose-6-phosphate dehydrogenase (D-glucose 6-phosphate: nicotinamide adenine dinucleotide phosphate oxidoreductase, EC 1.1.1.49) (G-6-PD) can be dissociated into smaller sub-units under certain conditions1–4, which suggests that normal and variant human G-6-PD may be hybridized in vitro. Studies of such hybridization may provide information on the polypeptide chains in which mutation occurred. Hybridization between human and rat G-6-PD has been observed5, but despite the attempts made6, no successful hybridization has so far been reported between the normal and variant human G-6-PD. We report here in vitro hybridization of the normal (B +), the common Negro variant with normal red cell enzyme activity (A +) and the Seattle variant7.

Some red cell enzyme activities in paroxysmal nocturnal haemoglobinuria.

Some red cell enzyme activities in paroxysmal nocturnal haemoglobinuria.