Feedback inhibition of glutamine synthetase from green pea seeds

Reduced Liver Lipid Peroxidation in Subcellular Fractions Is Associated with a Hypometabolic State in Rats with Portacaval Anastomosis

A surgical connection between portal and inferior cava veins was performed to generate an experimental model of high circulating ammonium and hepatic hypofunctioning. After 13 weeks of portacaval anastomosis (PCA), hyperammonemia and shrinkage in the liver were observed. Low glycemic levels accompanied by elevated levels of serum alanine aminotransferase were recorded. However, the activity of serum aspartate aminotransferase was reduced, without change in circulating urea. Histological and ultrastructural observations revealed ongoing vascularization and alterations in the hepatocyte nucleus (reduced diameter with indentations), fewer mitochondria, and numerous ribosomes in the endoplasmic reticulum. High activity of hepatic caspase-3 suggested apoptosis. PCA promoted a marked reduction in lipid peroxidation determined by TBARs in liver homogenate but specially in the mitochondrial and microsomal fractions. The reduced lipoperoxidative activity was also detected in assays supplemented with Fe²⁺. Only discreet changes were observed in conjugated dienes. Fluorescent probes showed significant attenuation in mitochondrial membrane potential, reactive oxygen species (ROS), and calcium content. Rats with PCA also showed reduced food intake and decreased energy expenditure through indirect calorimetry by measuring oxygen consumption with an open-flow respirometric system. We conclude that experimental PCA promotes an angiogenic state in the liver to confront the altered blood flow by reducing the prooxidant reactions associated with lower metabolic rate, along with significant reduction of mitochondrial content, but without a clear hepatic dysfunction.

Development and evaluation of pneumococcal conjugate vaccines: clinical trials and control tests

Streptococcus pneumoniae is a major cause of pneumonia, meningitis, and otitis media and is responsible for disease in young children, the elderly, and immunocompromised individuals. Emerging high-level resistance to penicillin, multiple antibiotics, and tolerance to vancomycin emphasizes the importance of preventing pneumococcal infection by alternative methods such as immunization. The development of pneumococcal conjugate vaccines using the same carrier proteins as those used in Hemophilus influenzae type b vaccines has enhanced the immune response in infants and children compared with polysaccharide vaccines and has significantly improved the ability to prevent pneumococcal disease in this population worldwide. Here we review the clinical trials of multivalent pneumococcal conjugate vaccines under evaluation, identify potential carrier proteins considered for development of future pneumococcal conjugate vaccines, discuss issues regarding licensure of new candidate vaccines from a clinical trial and quality control perspective, and alternative vaccine strategies for the prevention of pneumococcal disease.

Effects of amino acids, adenine nucleotides and inorganic pyrophosphate on glutamine synthetase from Anabaena cylindrica

Glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2) from Anabaena cylindrica was inhibited by alanine, glycine, serine and aspartate. The effects of alanine and serine were uncompetitive with respect to glutamate, while those of glycine and asparatate were uncompetitive with respect to glutamate, while those of glycine and aspartate were non-competitive and mixed type respectively. Different pairs of amino acids and their various combinations caused a cumulative inhibition of the enzyme activity. Glutamine synthetase was also inhibited by ADP and AMP and both nucleotides affected the enzyme competitively with respect to ATP and non-competitively for glutamate. Inorganic pyrophosphate, between 2 and 3 mM, produced a very pronounced inhibiton of enzyme activity. The inhibition by PPi was uncompetitive for ATP. Various combinations of the adenine nucleotides, PPi and Pi exerted a cumulative inhibitory effect on the enzyme activity, as did the amino acids, in different combinations with either adenine nucleotides, PPi or Pi. The effects of the adenine nucleotides and the amino acids were more pronounced at higher concentrations of ammonia. Except for serine similar responses of these effectors were obtained with increasing concentrations of Mg2+. It is proposed that changes in the free concentrations of Mg2+ are important in energy-dependent regulation of the enzyme activity in this alga.

The control of glutamine synthetase level in Lemna minor L

The specific activity of glutamine synthetase (E.C. 6.3.1.2) of Lemna minor L. is markedly reduced when either ammonium ions or glutamine are present in the growth medium. Combinations of 5 mM ammonia and 5 mM glutamic acid or 5 mM ammonia and 5 mM glutamine as nitrogen source, lead to a 4-5 fold reduction of the maximum activity measurable on 5 mM γ-aminobutyric acid. Analyses of the soluble pool of nitrogen indicate that the reduction in enzyme level is associated with an increase in the pool of glutamine. There is an inverse correlation between the apparent rate of synthesis of glutamine synthetase and the intracellular concentration of glutamine, and this relationship suggests that the glutamine synthetase of Lemna minor is subject to end product repression by the endogenous pool of glutamine.