Stereospecific features of the conformative response of L-asparaginase

Clinical impacts of the concomitant use of L-asparaginase and total parenteral nutrition containing L-aspartic acid in patients with acute lymphoblastic leukemia

Introduction

L-asparaginase (ASNase) depletes L-asparagine and causes the death of leukemic cells, making it a mainstay for the treatment of acute lymphoblastic leukemia (ALL). However, ASNase's activity can be inhibited by L-aspartic acid (Asp), which competes for the same substrate and reduces the drug's efficacy. While many commercially used total parenteral nutrition (TPN) products contain Asp, it is unclear how the concomitant use of TPNs containing Asp (Asp-TPN) affects ALL patients treated with ASNase. This propensity-matched retrospective cohort study evaluated the clinical effects of the interaction between ASNase and Asp-TPN.

Methods

The study population included newly diagnosed adult Korean ALL patients who received VPDL induction therapy consisting of vincristine, prednisolone, daunorubicin, and Escherichia coli L-asparaginase between 2004 and 2021. Patients were divided into two groups based on their exposure to Asp-TPN: (1) Asp-TPN group and (2) control group. Data, including baseline characteristics, disease information, medication information, and laboratory data, were collected retrospectively. The primary outcomes for the effectiveness were overall and complete response rates. Relapse-free survival at six months and one year of treatment were also evaluated. The safety of both TPN and ASNase was evaluated by comparing liver function test levels between groups. A 1:1 propensity score matching analysis was conducted to minimize potential selection bias.

Results

The analysis included a total of 112 ALL patients, and 34 of whom received Asp-TPN and ASNase concomitantly. After propensity score matching, 30 patients remained in each group. The concomitant use of Asp-TPN and ASNase did not affect the overall response rate (odds ratio [OR] 0.53; 95% confidence interval [CI] = 0.17–1.62) or the complete response rate (OR 0.86; 95% CI = 0.29–2.59) of the ASNase-including induction therapy. The concomitant use of Asp-TPN and ASNase also did not impact relapse-free survival (RFS) at six months and one year of treatment (OR 1.00; 95% CI = 0.36–2.78 and OR 1.24; 95% CI, 0.50–3.12, respectively). The peak levels of each liver function test (LFT) and the frequency of LFT elevations were evaluated during induction therapy and showed no difference between the two groups.

Conclusion

There is no clear rationale for avoiding Asp-TPN in ASNase-treated patients.

Biotransformation of benzaldehyde by Saccharomyces cerevisiae: characterization of the fermentation and toxicity effects of substrates and products

Although higher initial rates of phenylacetyl carbinol formation were observed in fermentations containing a high starting benzaldehyde level, a massive reduction in yeast viability was observed resulting in early cessation of production formation. Pulse feeding to maintain lower benzaldehyde concentrations resulted in a lower initial reaction rate, but prolonged yeast viability and the biotransformation. This resulted in higher overall product tilers. As benzaldehyde concentration was increased, yeast growth rate was reduced (0.5 g/L), inhibited (1-2 g/L), or cell viability reduced (3 g/L). Benzaldehyde appeared to alter the cell permeability barrier to substrates and products. Reductions in yeast biomass levels and especially protein and lipid content were observed during the biotransformation. The effects of benzaldehyde and reaction products on yeast pyruvate decarboxylase and alcohol dehydrogenase stability were determined. Homogenized yeast cells produced similar phenylacetyl carbinol levels to whole yeast only if supplemented with thiamine pyrophosphate and magnesium.

States and functions of tyrosine residues in Escherichia coli asparaginase II

The importance of five tyrosine residues of Escherichia coli asparaginase II (EcA2) for catalysis and protein stability was examined by site-directed mutagenesis, chemical modification of wild-type and variant enzymes, and by thermodynamic studies of protein denaturation. While the tyrosine residue Y25 is directly involved in catalysis, the hydroxyl groups of residues Y181, Y250, Y289 and Y326 are not necessary for EcA2 activity. However, residues Y181 and Y326 are crucial for stabilization of the native EcA2 tetramer. pH titration curves showed that the active-site residue Y25 has a normal pKa while the C-terminal Y326 is unusually acidic. 1H-NMR signals of a peculiar ligand-sensitive tyrosine residue were assigned to Y25. These and other data suggest that a peptide loop (residues 14-27) which shields the active site during catalysis is highly flexible in the free enzyme.

Structural characterization of Pseudomonas 7A glutaminase-asparaginase

The amino acid sequence and a 2-A-resolution crystallographic structure of Pseudomonas 7A glutaminase-asparaginase (PGA) have been determined. PGA, which belongs to the family of tetrameric bacterial amidohydrolases, deamidates glutamine and asparagine. The amino acid sequence of PGA has a high degree of similarity to the sequences of other members of the family. PGA has the same fold as other bacterial amidohydrolases, with the exception of the position of a 20-residue loop that forms part of the active site. In the PGA structure presented here, the active site loop is observed clearly in only one monomer, in an open position, with a conformation different from that observed for other amidohydrolases. In the other three monomers the loop is disordered and cannot be traced. This phenomenon is probably a direct consequence of a very low occupancy of product(s) of the enzymatic reaction bound in the active sites of PGA in these crystals. The active sites are composed of a rigid part and the flexible loop. The rigid part consists of the residues directly involved in the catalytic reaction as well as residues that assist in orienting the substrate. Two residues that are important for activity residue on the flexible loop. We suggest that the flexible loops actively participate in the transport of substrate and product molecules through the amidohydrolase active sites and participate in orienting the substrate molecules properly in relation to the catalytic residues.

On the role of histidine and tyrosine residues in E. coli asparaginase. Chemical modification and 1H-nuclear magnetic resonance studies

The relative importance of tyrosine and histidine residues for the catalytic action of Escherichia coli asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) was studied by chemical modification and 1H-NMR spectroscopy. We show that, under appropriate reaction conditions, N-bromosuccinimide (NBS) as well as diazonium-1H-tetrazole (DHT) inactivate by selectively modifying two tyrosine residues per asparaginase subunit without affecting histidyl moieties. We further show that diethyl pyrocarbonate (DEP), a reagent considered specific for histidine, also modifies tyrosine residues in asparaginase. Thus, inactivation of the enzyme by DEP is not indicative of histidine residues being involved in catalysis. In 1H-nuclear magnetic resonance (NMR) spectra of asparaginase signals from all three histidine residues were identified. By measuring the pH dependencies of these resonances, pKa values of 7.0 and 5.8 were derived for two of the histidines. Titration with aspartate which tightly binds to the enzyme at low pH strongly reduced the signal amplitude of the pKa 7 histidyl moiety as well as those of resonances of one or more tyrosine residues. This suggests that tyrosine and histidine are indeed constituents of the active site.

The 18O isotope effect in 13C nuclear magnetic resonance spectroscopy: mechanistic studies on asparaginase from Escherichia coli

The mechanism of the enzyme asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) from Escherichia coli was examined using 13C NMR spectroscopy. The pH-dependent oxygen exchange reactions between water and aspartic acid were followed by use of the 18O isotope-induced shift of the resonance positions of directly bonded 13C nuclei. Both L-1- and L-1,4-[13C]aspartic acid were used in experiments with previously 18O-labeled aspartic acid, or in experiments involving the use of 18O-labeled solvent water. Asparaginase catalyzes a relatively efficient exchange between the oxygens of water and those on one carboxyl group of aspartic acid. Exchange at C-4 occurs rapidly but, within experimental error, no exchange at C-1 could be detected. These and related experiments involving the position of 18O incorporation during hydrolysis of aspartic acid beta-methyl ester are all consistent with possible acyl-enzyme mechanisms involving C-4, but do not support a free aspartic acid anhydride mechanism.

Interaction between L-aspartic acid and L-asparaginase from Escherichia coli: binding and inhibition studies

Experiments using equilibrium dialysis and fluorescence quenching provided direct evidence that approximately four moles of L-aspartic acid were bound per mole of tetrameric L-asparaginase from Escherichia coli, with a dissociation constant on the order of 60-160 microM. In addition, a set of weaker binding sites with a dissociation constant in the millimolar range were detected. Kinetic studies also revealed that L-aspartic acid inhibited L-asparaginase competitively, with an inhibition constant of 80 microM at micromolar concentrations of L-asparagine; at millimolar concentrations of the amide, an increase in maximal velocity but a decrease in affinity for L-asparagine were observed. L-Aspartic acid at millimolar levels again displayed competitive inhibition. These and other observations suggest that L-aspartic acid binds not only to the active site but also a second site with lower intrinsic affinity for it. The observed "substrate activation" is most likely attributable to the binding of a second molecule of L-asparagine rather than negative cooperativity among the tight sites of the subunits of this tetrameric enzyme. Further support for L-aspartic acid binding to the active site comes from experiments in which the enzyme, when exposed to various group-specific reagents suffered parallel loss of catalytic activity and in its ability to bind L-aspartic acid. Different commercial preparations of Escherichia coli L-asparaginase were found to contain approximately 2-4 moles of L-aspartic acid; these were incompletely removed by dialysis, but could be removed by transamination or decarboxylation. Efficiency of dialysis increased with increasing pH. Taken together, this set of results is consistent with the existence of a covalent beta-aspartyl enzyme intermediate.

Determination of the binding constant of ligand to protein by thermal inactivation tehnique. Effect of two binding sites

Theoretical considerations on the determining the binding constants (eta) of ligands to proteins were carried out. Whereas for a one-subunit protein the relationship between thermal inactivation rates and ligand concentration there is a simple linear function, for a protein with two subunits, a second-order relationship is derived. If the theory for one-subunit proteins is applied to multi-subunit proteins, the derived values of eta tend to be lower than the real binding constants. A method of determining the ligand binding constant for a two-subunit protein is described.