Fernando Climent

Effects of Thyroid Hormone on mRNAs of Phosphoglycerate Mutase Subunits in Rat Muscle during Development

Background: We previously showed that triiodothyronine (T3) stimulates muscle phosphoglycerate mutase (PGAM) activity and isozyme transition in rat skeletal and cardiac muscles. Methods: The effects of T3 on PGAM types B and M subunit expression in rat muscle during development are reported. Results: T3 administration during the first 21 days of rat life more than doubles type M PGAM mRNA levels, but produces minor effects on type B PGAM mRNA levels. The antihormone propylthiouracil (PTU) slightly decreases both type B and M mRNA levels, but this decrease is not statistically significant. Conclusion: Thyroid hormone influences PGAM mRNA isozyme levels differently and increases type M mRNA.

Effect of vanadate on phosphoryl transfer enzymes involved in glucose metabolism

Different types of enzymes from yeast and from rabbit muscle which catalyze phosphoryl transfer reactions involved in glucose metabolism differ in their sensitivity to vanadate. Phospho glucomutase and phosphoglycerate mutase are inhibited at the μM range. 2,3-Bisphosphoglycerate phosphatase is completely inhibited by 0.5 mM vanadate. 2,3-Bisphosphoglycerate synthase, hexokinase, phosphoglycerate kinase and fructose-1,6-P2 phosphatase are partially inhibited by mM vanadate. Phosphofructokinase and pyruvate kinase are not affected. The glycolytic enzymes which mechanism does not involves phosphoryl transfer step are not affected by vanadate.

Vanadate increases oxygen affinity and affects enzyme activities and membrane properties of erythrocytes

Abstract Incubation of blood with vanadate markedly increases the affinity of hemoglobin for oxygen, decreases the deformability of erythrocytes, reduces their osmotic fragility and alters their morphology, determining the appearance of equinocytic forms. Since vanadate is easily taken up by the erythrocytes and binds hemoglobin, these effects might result from interactions of vanadate with hemoglobin and with membrane proteins at the glycerate-2, 3-P 2 and/or ATP binding site. In addition, vanadate inhibits phosphoglycerate mutase, phosphoglucomutase and adenylate-kinase activities from hemolysates, suggesting a possible inhibitory effect on erythrocyte metabolism

Red cell glycolytic enzyme disorders caused by mutations: an update.

Glycolysis is one of the principle pathways of ATP generation in cells and is present in all cell tissues; in erythrocytes, glycolysis is the only pathway for ATP synthesis since mature red cells lack the internal structures necessary to produce the energy vital for life. Red cell deficiencies have been detected in all erythrocyte glycolytic pathways, although their frequencies differ owing to diverse causes, such as the affected enzyme and severity of clinical manifestations. The number of enzyme deficiencies known is endless. The most frequent glycolysis abnormality is pyruvate kinase deficiency, since around 500 cases are known, the first of which was reported in 1961. However, only approximately 200 cases were due to mutations. In contrast, only one case of phosphoglycerate mutase BB type mutation, described in 2003, has been detected. Most mutations are located in the coding sequences of genes, while others, missense, deletions, insertions, splice defects, premature stop codons and promoter mutations, are also frequent. Understanding of the crystal structure of enzymes permits molecular modelling studies which, in turn, reveal how mutations can affect enzyme structure and function.

2,3-Bisphosphoglycerate-independent phosphoglycerate mutase is conserved among different phylogenic kingdoms

We have previously demonstrated that maize (Zea mays) 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (PGAM-i) is not related to 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase. With the aid of specific anti-maize PGAM-i antibodies, we demonstrate here the presence of a closely related PGAM-i in other plants. We also describe the isolation and sequencing of a cDNA-encoding almond (Prunus amygdalus) PGAM-i that further demonstrates this relationship among plant PGAM-i. A search of the major databases for related sequences allowed us to identify some novel PGAM-i from different sources: plants (Arabidopsis thaliana, Oryza sativa and Antithamniom sp.), monera (Escherichia coli, Bacillus subtilis and Bacillus megaterium) and animals (Caenorhabditis elegans). All of these amino acid sequences share a high degree of homology with plant PGAM-i. These observations suggest that the PGAM-i from several biological kingdoms constitute a family of protein different from other proteins with related enzymatic function and arose from a common ancestral gene that has diverged throughout its evolution.

Sequence of rat skeletal muscle phosphoglycerate mutase cDNA

A cDNA clone coding rat skeletal muscle phosphoglycerate mutase was isolated from a rat muscle lambda gt10 cDNA library and its sequence was determined. The deduced protein possesses 252 amino acids and is 94% homologous with respect to human muscle phosphoglycerate mutase. No amino acids changes occur at the active site and structural predictions suggest strong conformational homologies with other enzymes of the mutase family.

Effect of vanadate on the formation and stability of the phosphoenzyme forms of 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase and of phosphoglucomutase

2,3-Bisphosphoglycerate-dependent phosphoglycerate mutase (2,3-bisphospho-D-glycerate:2-phospho-D-glycerate phosphotransferase, EC 2.7.5.3) and phosphoglucomutase (alpha-D-glucose-1,6-bisphosphate:alpha -D-glucose-1-phosphate phosphotransferase, EC 2.7.5.1), which are markedly inhibited by vanadate, possess a ping-pong mechanism involving an intermediate phosphoenzyme. The formation and the stability of these phosphoenzymes have been examined spectrophotometrically in the absence of vanadate. Vanadate does not inhibit the phosphorylation of either mutase by its cofactor. The instability of the phosphoenzyme form of phosphoglycerate mutase increases in the presence of vanadate, but the stability of the phosphorylated phosphoglucomutase is not affected.

Inhibition of phosphoglucomutase by fructose 2,6-bisphosphate

Fructose 2,6-bisphosphate inhibits phosphoglucomutase. The inhibition is mixed with respect to glucose 1,6-bisphosphate and non-competitive with respect to glucose 1-phosphate. In contrast with fructose 1,6-bisphosphate and glycerate 1,3-bisphosphate, which also possess inhibitory effect, fructose 2,6-bisphosphate does not phosphorylate phosphoglucomutase. Fructose 2,6-bisphosphate preparations contain contaminants which can explain artefactual results previously reported.

Immunological properties of rat phosphoglycerate mutase isozymes

In mammalian tissues three phosphoglycerate mutase (D-phosphoglycerate 2,3-phosphomutase, EC 5.4.2.1) isozymes result from the homo-dimeric and hetero-dimeric combinations of two subunits (types M and B). Whereas rabbit antisera against type M subunit (purified from rat muscle) and against type BB isozyme (purified from rat brain) possessed a high degree of specificity, both antisera reacted with type BB and MM isozymes, as demonstrated by immunoneutralization and ELISA. Both the M subunit and B subunit were more immunoreactive than their respective dimeric isozymes. Subunits type M and B may possess common antigenic determinants, and some of these determinants may be sterically hindered in their dimeric structures.

Effects of hypoxia and thyroid hormone on mRNA levels and activity of phosphoglycerate mutase in rabbit tissues.

Aim: In the present work, we studied the effects of hypoxia and triiodothyronine (T3) on phosphoglycerate mutase (PGAM) activity and expression in rabbit liver, brain, and skeletal muscle under in vivo conditions. Methods: Hypoxia was induced in a methacrylate cage with a mixture of 90% nitrogen and 10% oxygen. Hyperthyroidism was induced daily by T3 injection (250 µg/kg). Results: Hypoxia increases the PGAM activity in liver and brain, tissues which possess type PGAM-BB isozyme, but does not affect the PGAM activity in muscle which possesses type PGAM-MM isozyme. T3 administration increases the PGAM activity in muscle and liver, but does not affect the enzyme activity in the brain. In all cases, the activity changes in parallel with those of PGAM mRNA levels. Conclusion: The tissue-specific effects of hypoxia and T3 could be explained by the tissue-specific distribution of both PGAM isozyme and T3 receptors.