Phosphorylation Mechanism of N-Acetyl-l-glutamate Kinase, a QM/MM Study

In microorganisms and plants, N-acetyl-l-glutamate kinase (NAGK) catalyzes the second step in l-arginine synthesis, the phosphorylation of N-Acetyl-l-glutamate (NAG) to give N-acetyl-l-glutamate-5-phosphate. NAGK is only present in microorganisms and plants but absent in mammals, which makes it an attractive target for antimicrobial or biocidal development. Understanding the substrate binding mode and reaction mechanism of NAGK is crucial for targeting the kinase to develop potential therapies. Here, the substrate binding mode was studied by comparing the conformational change of NAGK in the presence and in the absence of the NAG substrate based on molecular dynamics simulations. We revealed that with substrate binding, the catalytic site of the kinase involving three loops in NAGK exhibits a closed conformation, which is predominantly controlled by an interaction between Arg98 and the α-COO^- of NAG. Lys41 is found to guide phosphate transfer through the interactions with the β-,γ-, and γ-phosphate oxygen atoms of adenosine 5'-triphosphate surrounded by two highly conserved glycine residues (Gly44 and Gly76), while Arg98 helps to position the NAG substrate in the catalytic site, which facilitates the phosphate transfer. Furthermore, we elucidated phosphate-transfer reaction mechanism using hybrid density functional theory-based quantum mechanics/molecular mechanics calculations (B97D/AMBER99) and found that the catalysis follows a dissociative mechanism.

Current and emerging pharmacotherapy for emergency management of preeclampsia

INTRODUCTION

Preeclampsia is a disease specific to pregnancy characterised by new onset hypertension with maternal organ dysfunction and/or fetal growth restriction. It remains a major cause of maternal and perinatal morbidity and mortality. For fifty years, antihypertensives have been the mainstay of treating preeclampsia, reducing maternal morbidity and mortality. With increased knowledge of the mechanisms underlying the disease has come opportunities for novel therapies that complement antihypertensives by protecting the maternal vasculature. Areas covered: In this review, the authors consider, in detail, the antihypertensives commonly used today in the emergency care of women with severe preeclampsia. They also review less common anti-hypertensive agents and discuss the role of magnesium sulphate in the management of preeclampsia and the prevention of eclampsia. Finally, they explore novel therapeutics for the acute management of preeclampsia. Expert opinion: The rapid control of maternal hypertension will, and must, remain the mainstay of emergency treatment for women with severe preeclampsia. The role of magnesium sulphate as a primary prevention for eclampsia is context dependant and should not displace a focus on correcting blood pressure safely. The exploration of novel adjuvant therapies will likely allow us to prolong pregnancy longer and improve perinatal outcomes safely for the mother.

Effects of acute L-arginine infusion on non-stress test in hypertensive pregnant women

OBJECTIVE

The present report evaluates the effect of acute L-arginine administration on fetal heart variables by a computerized non-stress test (NST) analysis.

METHODS

Fifteen pregnant women at 30-34 weeks of gestational age affected by mild to moderate gestational hypertension were enrolled in the study. The study was performed in the second and third days of hospitalization. Each woman received both active (Arg) or placebo treatment (Placebo), in a double-blind, randomized, cross-over design. Women received saline infusion for 40 min, then they were infused with either placebo (saline infusion prepared by Damor Pharmaceutics and labeled as Arg-B) or Arg (L-Arg 20 g/500 ml labeled as Arg-A).

RESULTS

Multiple analysis of variance (MANOVA) indicated that both placebo and Arg infusion were unable to affect cardiac variables and fetal movements. As far as maternal blood pressure changes were concerned, MANOVA indicated that active treatment showed an acute hypotensive effect on both systolic (F=8.98, p<0.001) and diastolic values (F=15.78, p>0.001). Conversely, placebo infusion does not seems to have induced any change. Considering each time of infusion we observed that Arg treatment was able to lower systolic and diastolic blood pressure after the 40 min of infusion, with this effect persisting for 20 min.

CONCLUSIONS

These data indicate that the acute, intravenous administration of high-dose L-arginine does not induce significant changes in fetal heart rate (FHR), whereas it lowers maternal blood pressure. Such conclusions are reinforced by the observation that saline administration in the same pregnant women was neutral for both FHR and maternal blood pressure values. According to previous studies, it seems conceivable that maternal L-arginine treatment enters the fetal circulation by crossing the placenta. The lack of changes in FHR, however, suggests that no significant hemodynamic changes were induced by the treatment. Contrary to what happens in the mother, this may possibly be due to a low, if any, conversion of L-arginine to nitric oxide in the fetus.