ECAR-LANS, the recombinant L-asparaginase fromErwinia carotovora, is a prospective therapeutic enzyme for leukaemia treatment. An efficient and economical scheme was developed for the purification, cloning and expression in Eschericha coli of ECAR-LANS. More than 90 % purity, complemented with 72 % active enzyme recovery, was achieved with a single chromatographic purification step. The activity of purified L-asparaginase was 630 i.u./mg. The ECAR-LANS K m value was 98 × 10 −6 M for the main physiological substrate L-Asn and 3400 × 10 −6 M for L-Gln. ECAR-LANS was found to have low relative glutaminase activity (1.2 %) at physiological concentrations of L-Asn and L-Gln in blood. Kinetic studies of ECAR-LANS showed that the recombinant asparaginase combined the main advantages of Erw. chrysanthemi and E. coli L-asparaginases II, currently used in the treatment of acute lymphoblastic leukaemia.

Information accumulated over the past decades on the physiological functions and metabolic pathways of biosynthesis and degradation of D-amino acids has led to a renewed interest in their study. These isomers are known to form both in nature and during the chemical synthesis of L-amino acids for feeding and pharmacological purposes, as well as in the industrial processing of some raw materials. This article discusses the positive and negative effects of D-amino acids on the human body, animals and the environment. In addition, the scientific data concerning the mechanisms of cytotoxic action of D-amino acids and their industrial and biomedical potential are summarized. ARTICLE HISTORY

Site-directed mutagenesis of Rhodospirillum rubrum L-asparaginase (RrA) was performed in order to identify sites of the protein molecule important for its therapeutic and physico-chemical properties. Ten multipoint mutant genes were obtained, and five recombinant RrA variants were expressed in E. coli BL21(DE3) cells and isolated as functionally active highly purified proteins. Protein purification was performed using Q-Sepharose and DEAE-Toyopearl chromatography. Overall yield of the active enzymes was 70-80 %, their specific activity at pH 7.4 and 37 °C varied of 140-210 U/mg. L-Glutaminase activity did not exceed 0.01 % of L-asparaginase activity. All RrA mutants showed maximum enzyme activity at pH 9.3-9.5 and 53-58 °C. Km and Vmax values for L-asparagine were evaluated for all mutants. Mutations G86P, D88H, M90K (RrAH), G121L, D123A (RrАI) caused the loss of enzyme activity and confirmed the importance of these sites in the implementation of catalytic functions. Removal of four residues from C-terminal area of the enzyme (RrAK) resulted in the enzyme instability. Mutations D60K, F61L(RrАD), and R118H, G120R(RrАJ) led to the improvement of kinetic parameters and enzyme stabilization. Substitutions E149R, V150P (RrАB) improved antineoplastic and cytotoxic activity of the RrA. A64V, E67K substitutions, especially in combination with E149R, V150P (RrАE), considerably destabilized recombinant enzyme.

Bacterial l‐asparaginases are enzymes that catalyze the hydrolysis of l‐asparagine to aspartic acid. For the past 30 years, these enzymes have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. Their intrinsic low‐rate glutaminase activity, however, causes serious side‐effects, including neurotoxicity, hepatitis, coagulopathy, and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side‐effects in leukemia therapy. To gain detailed insights into the properties of E. carotovora asparaginase, combined crystallographic, thermal stability and cytotoxic experiments were performed. The crystal structure of E. carotovoral‐asparaginase in the presence of l‐Asp was determined at 2.5 Å resolution and refined to an Rcryst of 19.2 (Rfree = 26.6%) with good stereochemistry. Cytotoxicity measurements revealed that E. carotovora asparaginase is 30 times less toxic than the Escherichia coli enzyme against human leukemia cell lines. Moreover, denaturing experiments showed that E. carotovora asparaginase has decreased thermodynamic stability as compared to the E. coli enzyme and is rapidly inactivated in the presence of urea. On the basis of these results, we propose that E. carotovora asparaginase has limited potential as an antileukemic drug, despite its promising low glutaminase activity. Our analysis may be applicable to the therapeutic evaluation of other asparaginases as well.

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The recombinant producer strain expressing Rhodospirillum rubrum L asparaginase (RrA) has been obtained and a purification procedure of RrA has been developed. The purified enzyme, RrA, has the following biochemical and catalytic characteristics: K m for L Asn of 0.22 mM, pH optimum at 9.2; temper ature optimum at 54°C, pI = 5.1. RrA exhibited a significant cytotoxic effect towards the following cell lines: K562 (IC 50 = 1.80 U/mL), DU145 (IC 50 = 9.19 U/mL), and MDA MB 231 (IC 50 = 34.62 U/mL). Com parative analysis employing E. coli L asparaginase II type (EcA) and Erwinia carotovora L asparaginase (EwA) has shown that the enzyme cytotoxicity towards these cell lines decreased in the following order: EcA > RrA > EwA. Daily administration of RrA (4000 U/kg) to L5178y bearing mice for 10 days (total dose of 40000 U/kg) showed T/C = 172. Data obtained suggest that RrA may be referred to intracellular L aspar aginases with low L glutaminase activity and marked antiproliferative effect.

The recombinant producer of Rhodospirillum rubrum L-asparaginase (RrA) was received and purification procedure of RrA was developed. It was shown that RrA has following biochemical and catalytic characteristics: K for L-asn 0,22 мM, pH optimum 9,2; temperature optimum 54°С; pI=5,1±0,3; L-gln activity seems to be low-to-negligible. К562, DU145 and MDA-MB-231 cellular lines displayed significant sensitivity towards the enzyme (IC50=1,80; 9,19 and 34,62 ME/ml, respectively. In comparison with L-asparaginases from E . coli II type (EcA) and Erwinia carotovora (EwA) cytotoxicity of RrA seems to be higher than EwA, but lower than EcA. 10-fold i.p. RrA administration (4000 ME/kg per day) in L5178y bearing mice showed Т/С=172%. The received results show that RrA belongs to I type cellular L-asparaginases with low L-gln activity and the high antiproliferative effect.

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