Purification of glucosamine 6-phosphate deaminase from human brain

UDP-N-acetylglucosamine pyrophosphorylase, a key enzyme in encysting Giardia, is allosterically regulated

Giardia synthesizes UDP-GalNAc during cyst wall formation (encystment) via a pathway of inducible enzymes similar to that used to synthesize chitin or peptidoglycan and that includes the UTP-requiring UDP-N-acetylglucosamine pyrophosphorylase. Although it has never been reported as a regulatory enzyme in any system studied to date, kinetic data including Hill plots demonstrate clearly that UDP-N-acetylglucosamine pyrophosphorylase activity, purified from encysting Giardia, is allosterically activated anabolically by physiological levels of glucosamine 6-phosphate (3 microm). Capillary electrophoresis demonstrates that within 24 h after trophozoites are induced to encyst, the level of glucosamine 6-phosphate increases 3-fold over that of non-encysting cells and that by 48 h into encystment the level of glucosamine 6-phosphate has decreased to non-encysting levels or below. UDP-N-acetylglucosamine pyrophosphorylase protein is present constitutively in encysting as well as non-encysting cells. UDP-N-acetylglucosamine pyrophosphorylase immunoaffinity purified from encysting and non-encysting cells exhibited the same molecular weight, amino acid composition, and circular dichroism spectra. Moreover, regardless of whether the enzyme came from encysting or non-encysting cells, the change in its circular dichroism spectra and up to a 6-fold increase in its specific activity anabolically were due to its activation with glucosamine 6-phosphate. Thus, the data support the idea that UDP-N-acetylglucosamine pyrophosphorylase is a major regulatory point in amino sugar synthesis in encysting Giardia and that its allosteric anabolic activation may shift the equilibrium of this pathway toward UDP-GalNAc synthesis.

Glucosamine-6-phosphate deaminase from beef kidney is an allosteric system of the V-type

The enzyme glucosamine-6-phosphate deaminase from beef kidney has been purified to homogeneity by allosteric-site affinity chromatography. Its amino acid composition and the N-terminal sequence (1-42), were obtained. The amino acid sequence of this segment is essentially identical to the corresponding regions of the human and hamster glucosamine-6-phosphate deaminases. The beef enzyme is a hexamer of 32.5 kDa subunits; this is nearly 2.5 kDa higher than the molecular mass of the homologous enzyme from Escherichia coli. Beef kidney deaminase exhibits a notable difference from the bacterial enzyme in its allosteric activation by N-acetylglucosamine 6-phosphate This metabolite, which is also is the allosteric activator of the bacterial glucosamine-6-phosphate deaminase, activates the enzyme by increasing its kcat without any change in the Km values for glucosamine 6-phosphate, over a wide range of activator concentration. This observation places beef kidney deaminase in the class of V-type allosteric systems.

The human glucosamine-6-phosphate deaminase gene: cDNA cloning and expression, genomic organization and chromosomal localization

When mammalian eggs are fertilized by sperm, a distinct series of calcium oscillations are generated which serve as the essential trigger for egg activation and early embryo development. The identification of a soluble hamster sperm 33-kDa protein that co-migrated with calcium oscillation-inducing activity was recently described by Parrington et al. (Parrington, J., Swann, K., Shevchenko, V.I., Sesay, A.K. and Lai, F.A., 1996. Calcium oscillations in mammalian eggs triggered by a soluble sperm protein. Nature 379, 364-368). The hamster sperm 33 kDa protein was termed oscillin because it correlated with calcium oscillation-inducing activity in mammalian eggs. Sequence analysis of the hamster sperm 33 kDa protein indicated no similarity to any known cell signalling molecule, however, it displayed extensive homology with a bacterial glucosamine-6-phosphate deaminase. We have isolated the corresponding human testis homologue of the hamster sperm 33 kDa cDNA. Nucleotide sequence analysis reveals a high level of sequence identity between the hamster and human genes. The deduced protein sequence of the human gene also shares extensive amino acid identity with the bacterial glucosamine-6-phosphate deaminase enzyme. Heterologous expression of the human testis 33 kDa protein produced a glucosamine-6-phosphate deaminase activity. The genomic structure of the human glucosamine-6-phosphate deaminase has been mapped and the gene was localized by fluorescence in situ hybridization (FISH) to chromosome 5q31.

FURTHER STUDIES ON THE REGULATION OF AMINO SUGAR METABOLISM IN BACILLUS SUBTILIS

1. Glucosamine 6-phosphate deaminase [2-amino-2-deoxy-d-glucose 6-phosphate ketol-isomerase (deaminating), EC 5.3.1.10] of Bacillus subtilis has been partially purified. Its K(m) is 3.0mm. 2. Extracts of B. subtilis contain N-acetylglucosamine 6-phosphate deacetylase (K(m) 1.4mm), glucosamine 1-phosphate acetylase and amino sugar kinases (EC 2.7.1.8 and 2.7.1.9). 3. Glucosamine 6-phosphate synthetase (l-glutamine-d-fructose 6-phosphate aminotransferase, EC 2.6.1.16) is repressed by growth of B. subtilis in the presence of glucosamine, N-acetylglucosamine, N-propionylglucosamine or N-formylglucosamine. Glucosamine 6-phosphate deaminase and N-acetylglucosamine 6-phosphate deacetylase are induced by N-acetylglucosamine. Amino sugar kinases are induced by glucose, glucosamine and N-acetylglucosamine. The synthesis of glucosamine 1-phosphate acetylase is unaffected by amino sugars. 4. Glucose in the growth medium prevents the induction of glucosamine 6-phosphate deaminase and of N-acetylglucosamine 6-phosphate deacetylase caused by N-acetylglucosamine; glucose also alleviates the repression of glucosamine 6-phosphate synthetase caused by amino sugars. 5. Glucosamine 6-phosphate deaminase increases in bacteria incubated beyond the exponential phase of growth. This increase is prevented by glucose.

Glucosamine 6-phosphate deaminase in Plasmodium falciparum

The pathways of glucose utilization for energy production in the malaria parasite, Plasmodium falciparum, have been studied extensively. Little is known, however, about the reactions by which glucose is converted into complex carbohydrates in the parasite, and knowledge of the catabolism of these substances is likewise scanty. The present investigation was undertaken to determine whether the parasites possess a key enzyme of glucosamine catabolism, i.e. glucosamine 6-phosphate deaminase (EC 5.3.1.40), which catalyses the conversion of the sugar phosphate to fructose 6-phosphate and ammonia. Lysates of Plasmodium-infected erythrocytes had substantially higher deaminase activity than control samples from normal erythrocytes, and an even higher specific activity was observed in extracts of isolated parasites, amounting to 20-40 times that of uninfected cells. Anion exchange chromatography indicated that the parasite deaminase eluted in a retarded position when compared to the elution profile of the erythrocyte enzyme. The charge difference suggested by these findings was established more directly by chromatofocusing, which indicated pI values of 6.85 and 8.55 for the parasite and erythrocyte deaminases, respectively. Other differences were also observed, notably a greater thermolability on the part of the parasite enzyme. These results indicated that the parasites synthesize a specific deaminase that is distinct from the normal erythrocyte enzyme. Studies on synchronized parasite cultures further indicated that the parasite deaminase is developmentally regulated, because a dramatic increase in activity levels occurred during the later stages of parasite development.

Glucosamine 6-phosphate deaminase in normal human erythrocytes

In the course of an investigation of hexosamine catabolism in the human malaria parasite, Plasmodium falciparum, it became apparent that a basic understanding of the relevant enzymatic reactions in the host erythrocyte is lacking. To acquire the necessary basic knowledge, we have determined the activities of several enzymes involved in hexosamine metabolism in normal human red blood cells. In the present communication we report the results of studies of glucosamine 6-phosphate deaminase (GlcN6-P) using a newly developed sensitive radiometric assay. The mean specific activity in extracts of fresh erythrocytes assayed within 4h of collection was 14.7 nmol/h/mg protein, whereas preparations from older erythrocytes that had been stored at 4 degrees C for up to 4 weeks had a mean specific activity of 6.2 nmol/h/mg. Characterization of the deaminase by chromatofocusing gave a pI of 8.55. The enzyme was optimally active at pH 9.0 and had a Km of 41 microM. The metal chelators EDTA and EGTA were non-inhibitory; however, inhibition was observed in the presence of metal ions, especially Cu2+, Ni2+ and Zn2+. In addition, the deaminase was also inhibited by several sugar phosphates including the reaction product, fructose 6-phosphate.

Purification and characterization of glucosamine-6-phosphate deaminase from dog kidney cortex

Glucosamine-6-phosphate deaminase (EC 5.3.1.10) from dog kidney cortex was purified to homogeneity, as judged by several criteria of purity. The purification procedure was based on two biospecific affinity chromatography steps, one of them using N-epsilon-amino-n-hexanoyl-D-glucosamine-6-phosphate agarose, an immobilized analog of the allosteric ligand, and the other by binding the enzyme to phosphocellulose followed by substrate elution, which behaved as an active-site affinity chromatography. The enzyme is an hexameric protein of about 180 kDa composed of subunits of 30.4 kDa; its isoelectric point was 5.7. The sedimentation coefficient was 8.3S, and its frictional ratio was 1.28, indicating that dog deaminase is a globular protein. The enzyme displays positive homotropic cooperativity toward D-glucosamine-6-phosphate (Hill coefficient = 2.1, pH 8.8). Cooperativity was completely abolished by saturating concentrations of GlcNAc6P; this allosteric modulator activated the reaction with a typical K-effect. Under hyperbolic kinetics, a Km value of 0.25 +/- 0.02 mM for D-glucosamine-6-phosphate was obtained. Assuming six catalytic sites per molecule, kcat is 42 s-1. Substrate-velocity data were fitted to the Monod's allosteric model for the exclusive-binding case for both substrate and activator, with two interacting substrate sites. The Kdis for N-acetyl-D-glucosamine-6-phosphate was estimated at 14 microM.

[Metabolism of glucosamine in the liver of Scyliorhinus canicula (selachian)]

(1) The metabolism of the glucosamine was studied in the liver of S. canicula, after injection of D-(1-14C) glucosamine into the animal. (2) The labelled acid-soluble derivatives were separated by ion exchange columns and characterized by chromatography and electrophoresis, and were identified as glucosamine, glucosamine 6-P, N-acetylglucosamine, N-acetylmannosamine, N-acetylneuraminic acid, N-acetylglucosamine 6-P, N-acetylglucosamine 1-P, N-acetylmannosamine 6-P, UDP-N-acetylglucosamine, UDP-N-acetylgalactosamine. (3) The variation with time after glucosamine injection of the radioactivity of the fractions separated on Dowex 1-X4 was investigated. This study showed a decrease of the radioactivity in the fraction 1 (glucosamine and glucosamine 6-P), an increase in the fraction II (N-acetylneuraminic acid) and the fraction IV (UDP-N-acetylhexosamines), and a stability in the fraction III (phosphorylated N-acetylhexosamines). (4) The absence of label in neutral hexoses and their phosphorylated derivatives was interpretated as due to the weak activity of the glucosamine 6-P isomerase, which is positively modulated by the N-acetylglucosamine 6-P.