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Biochemistry
Published in Ronald Fayer, Lihua Xiao, Cryptosporidium and Cryptosporidiosis, 2007
Although amino acids are the basic building blocks of proteins, Cryptosporidium apparently cannot synthesize any of them de novo. All amino acid synthetic genes are missing from the C. parvum genome. Instead, this parasite possesses at least 11 amino acid transporters for scavenging amino acids from host cells (and the intestinal lumen), in contrast to P. falciparum, which only possesses one amino acid transporter (Abrahamsen et al., 2004). However, C. parvum retains the capacity of interconverting a limited number of amino acids. Glutamate produced by GMP synthetase can be recycled back to glutamine (Gln) by glutamine synthetase (GS) (Figure 3.1). Serine (Ser) and glycine (Gly) may be interconverted by serine hydroxymethyl transferase (SHMT) within the folate metabolic pathway (Figure 3.1). Asparagine (Asn) can be made from aspartate (Asp) by asparagine synthetase, which might be important in the recycling of NH3 released by AMP deaminase. Other conversions include methionine (Met) and S-adenosylmethionine (SAM) by SAM synthetase, and homocysteine and S-adenosyl homocysteine (SAH) by SAH synthase. One small surprise is the presence of a single tryptophan synthase that may synthesize tryptophan (Trp) from indole or indoleglycerol phosphate within the Trp synthetic pathway.
A Review on L-Asparaginase
Published in Se-Kwon Kim, Marine Biochemistry, 2023
Asparagine synthetase is a large enzyme composed of two similar subunits. The given structure (Figure 9.1) has been referred to be the enzyme isolated from bacteria. This enzyme is solely responsible for the production of asparagine by combining with ammonia molecule directly to aspartic acid. The enzyme uses glutamine in the case of humans to give the amine instead of ammonia. L-asparaginase (Figure 9.2) is obtained in the purified form from the bacterial cells and is used in chemotherapy. It is composed of four identical subunits. Grip asparagine, which is the active site of the enzyme (red), makes use of a well-placed amino acid threonine (green) to perform the reaction of cleavage. L-asparaginase tetramer can be termed as a dimer of dimers because of the presence of each of the four active sites located in between the N- and C-terminal domains of two adjacent monomers. In spite of the existence of structural elements and functional groups to form a complete active site environment, the active L-asparaginase enzyme is regarded to be a tetramer with each domain containing one active center and catalysis of the hydrolysis of L-asparagine to L-aspartic acid and ammonia (Khushoo et al., 2004). Conserved residues strictly inhabit the formation of the active site. A flexible loop that is a part of the active site (between 10–40 residues) contains the residues threonine-12 and tyrosine-25 that are important. Threnine-12 is the nucleophile actively involved in the acylation reaction (Aung et al., 2000). It is this flexible loop that controls the access to the active site cavity that opens and closes in a ligand-dependent fashion (Aung et al., 2000; Kozak et al., 2002).
Enzymatic Amino Acid Deprivation Therapies Targeting Cancer
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Carla S. S. Teixeira, Henrique S. Fernandes, Sérgio F. Sousa, Nuno M. F. S. A. Cerqueira
l-Asparagine (l-ASN) is a non-essential amino acid that is synthesized in humans by the asparagine synthetase enzyme (Lomelino et al., 2017). However, l-ASN is indispensable for the synthesis of several proteins, in particular, the ones that are glycosylated through N-glycosylation (Cherepanova and Gilmore, 2016) Moreover, this amino acid is involved in the control of some cell functions in the nervous system, and also in the metabolism of ammonia to enable the elimination of this toxic metabolic by-product (Erecinska et al., 1991; Chen and Chen, 1992).
Synthesis and characterization of new bis(fluoroalkyl) phosphoramidates bearing sulfoximine groups
Published in Journal of Sulfur Chemistry, 2021
Hanen Mechi, M.A.K. Sanhoury, F. Laribi, M. T. Ben Dhia
Sulfoximines are considered as the monoaza analogs of sulfones and their stability has led to versatile chemistry [17,18]. In synthetic organic chemistry [19,20], the acidic α-hydrogen is one of the properties they share but the nitrogen atom offers the possibility for functionalization of molecules through nucleophilic reactions [21]. The widespread interest in the chemistry of sulfoximines is mainly due to the versatility of their applications in stereochemical studies [22–24]; they have been explored as building blocks in bioactive molecules [25,26] and often have very high efficiency in asymmetric metal catalysis [27]. In the literature some patents can be found on substituted sulfoximines for use as agrochemicals [28], detergents, additives, bacterial, antifungal compounds and auspicious bioisosteres in medicinal chemistry [29]. Some sulfoximine phosphoramidates are known for their important biological role [30–34]. For example, the active form of methionine sulfoximine, which efficiently inhibits glutamine synthetase, is methionine sulfoximine phosphate [30]. In addition, two nucleoside sulfoximine-containing phosphoramidates were shown to be potent inhibitors of human asparagine synthetase (hASNS) [31–33]. However, research studies on N-phosphorylated sulfoximines are still relatively rare and limited to a few examples [34,35–37]. As far as we are aware and despite the above mentioned interest in sulfoximine derived phosphoramidates and the versatile influence of inclusion of fluorine atoms on molecule properties [38–40], no reports on fluoroalkyl analogs have been yet described.
Optimisation of physical parameters pH and temperature for maximised activity and stability of Vibrio cholerae L-asparaginase by statistical experimental design
Published in Indian Chemical Engineer, 2021
Remya Radha, Sathyanarayana N. Gummadi
L-asparaginase (E.C.3.5.1.1) is an enzyme favours the hydrolytic breakdown of L-asparagine releasing its products L-aspartatic acid and ammonia. It is preferred in food processing industries to prevent Maillard’s browning reaction and there have been various reports monitoring the decline of acrylamide level by asparaginase usage [1]. In addition, asparaginases now become a cornerstone of the valuable treatment protocols for acute lymphoblastic leukaemia (ALL) and lymph sarcoma [2,3]. The antitumor activity of this protein is attributed to the depletion of L-asparagine patients. Since tumour cells lack the ability to synthesise L-asparagine synthetase, a key amino acid responsible for intracellular L-asparagine synthesis and thus they are effectively killed by L-asparagine deprivation [4,5].
Toxicity, metabolism, and mitigation strategies of acrylamide: a comprehensive review
Published in International Journal of Environmental Health Research, 2022
Leila Peivasteh-Roudsari, Marziyeh Karami, Raziyeh Barzegar-Bafrouei, Samane Samiee, Hadis Karami, Behrouz Tajdar-Oranj, Vahideh Mahdavi, Adel Mirza Alizadeh, Parisa Sadighara, Gea Oliveri Conti, Amin Mousavi Khaneghah
Asparagine synthetase catalyzes the ATP-dependent transfer of the amino group of glutamine to a molecule of aspartate to generate glutamate and asparagine (Halford 2018). Low AA genetically modified (GM) potato varieties have been developed by suppressing the expression of asparagine synthetase and starch phosphorylase genes of potato via genome modification and DNA transformation, which significantly decline synthesis of free asparagine and slow down starch breakdown during storage, consequently lowering the potential to form AA during cooking. A new generation of GM potatoes was produced by reduced expression of a vacuolar invertase gene, being less prone to cold sweetening (Halford et al. 2022)