In vivo lability of red cell phosphofructokinase in term infants: the possible molecular basis of the relative phosphofructokinase deficiency in neonatal red cells

Red cell enzymes and intermediates in AGA term newborns, AGA preterm newborns and SGA term newborns

Red cell enzyme activities and 2,3-diphosphoglycerate and adenosine-triphosphate levels in cord blood of three groups of newborn infants were studied. The groups were classified according to birthweight in relation to intrauterine growth and gestational age. Only phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and enolase activity values differed significantly among the groups. The activity of phosphofructokinase was lower in small-for-date term infants (TSGA) and preterm adequate for gestational age (PTAGA) in comparison to term infants adequate for gestational age (TAGA). Glyceraldehyde-3-phosphate dehydrogenase activity was higher in TAGA, in comparison to PTAGA, with no other difference among the groups. Enolase activity was found to be higher in TSGA compared to TAGA and higher in PTAGA compared to TAGA. No differences were found between PTAGA and TSGA.

Characteristics of hexokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase during adult and neonatal reticulocyte maturation

Erythrocytes from adults and newborn infants (at term and premature) were separated by Percoll density gradient centrifugation into four fractions of increasing density. Glycolytic enzymes, especially the age-dependent ones, hexokinase (EC 2.7.1.1, HK), pyruvate kinase (EC 2.7.1.40, PK), and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6PD) were studied during reticulocyte maturation and further red cell senescence. Analysis of the fraction with lowest density showed an almost linear and steep decline of HK, PK, and G6PD activity with a decreasing number of reticulocytes. In the next three fractions of increasing density, the activity decline was far less. These data are therefore illustrative for a biphasic activity decay pattern of HK, PK, and G6PD during both adult and neonatal red cell aging. The strong decline in HK activity could not be ascribed to the disappearance of a particulate (mitochondrial) bound fraction of the enzyme during reticulocyte maturation. All hexokinase activity in human reticulocytes was found to be cytosolic in contrast with rabbit reticulocytes in which 70% of HK activity was particulate.

Enzyme activities of cultured erythroblasts

The enzyme activities of cultured early erythroid progenitor cells (burst-forming unit erythroid, BFU-E) were measured and were compared with the activities of mature erythrocytes. The enzyme activity of acetylcholinesterase was not detectable in the erythroblasts. The ratios of phosphofructokinase and glutathione peroxidase were low due to low enzyme activities in both the erythroblasts and erythrocytes. The ratios of triose phosphate isomerase, phosphoglycerate kinase, and adenylate kinase were low due to high enzyme activities in both the erythroblasts and erythrocytes. The ratios of hexokinase, glucose phosphate isomerase, monophosphoglyceromutase, pyruvate kinase, and adenosine deaminase were high due to high enzyme activities in the erythroblasts. The isozyme of erythroblast hexokinase was of the prototype isozyme I, while pyruvate kinase was predominantly of the prototype M2, with two hybrid isozymes to the anodal side by electrophoresis. These facts suggest that there is a greatly different metabolic pattern during the maturation of the erythroid cells.

Alterations in phosphofructokinase isoenzymes during early human development. Establishment of adult organ-specific patterns

Human 6-phosphofructokinase (EC 2.7.1.11) exists in tetrameric isoenzymic forms composed of muscle (M), liver (L) and platelet (P) subunits, which are under separate genetic control. In the adult, the proportion of these subunits in different organs reflects the relative activity of glycolysis versus gluconeogenesis. To elucidate the developmental basis for the observed distribution, we investigated the isoenzymic transitions of phosphofructokinase in human foetuses (12-40 weeks' gestation) by using high-resolution chromatography and monoclonal antibodies. We studied skeletal muscle, heart, liver and brain because these organs show very different glycolytic fluxes and isoenzymic patterns in adult individuals. Our results demonstrate that there is no unique 'foetal' form of phosphofructokinase in humans, but all three loci are variably expressed in all foetal organs during early gestation. As development proceeds, muscle and liver isoenzyme patterns show dramatic changes, with disappearance of P and L subunits in muscle and transient reappearance of M and P subunits in liver; in contrast, phosphofructokinase isoenzymes change little in brain and heart. Most changes occur at mid-gestation and near term, and adult isoenzyme patterns are expressed at birth, indicating that organ differentiation is complete. These studies show that phosphofructokinase undergoes changes of isoenzyme patterns similar to, but not identical with, those of other multilocus isoenzyme systems of glycolysis. The observed changes probably reflect changing patterns of gene expression, with repression of some loci and activation of others.

Erythrocyte enzymes in Ovis aries. Effect of cell age

1. Activities of 20 red cell enzymes were compared in 8 normal female Ovis Aries, in a serially bled ewe followed by 243 days, and in young and old red cell populations separated by density gradient centrifugation. 2. These comparisons indicate that the erythrocyte enzymes which show significant changes with cell age are glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, hexokinase, phosphoglucose isomerase, lactate dehydrogenase, glutathione reductase, enolase and phosphoglycerate kinase. 3. The usefulness of these data in interpretation of enzyme activities from fetal Ovis Aries is discussed.