Enzymatic synthesis of cefazolin using immobilized recombinant cephalosporin-acid synthetase as the biocatalyst.

A method for the synthesis of ß-lactam antibiotic cefazolin (CEZ) by enzymatic acylation of 7-amino-3-(5-methyl-l,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylic acid (TDA) using immobilized cephalosporin-acid synthetase (IECASA) from recombinant E. coli strain VKPM B-12316 has been developed. A stepwise pH gradient designed on the basis of investigations on the solubility of components was applied for synthesis. This helped in avoiding the precipitation of TDA in the reaction when its initial concentration was high (150-200 mM). Thus, under optimal conditions a high yield of CEZ (relative to TDA) of 92-95% was obtained. Where the final reaction mixture contained 65-85 mg/mL of CEZ, 4-5 mg/mL of unreacted TDA, and 40-60 mg/mL of the by-product, 1(H)-tetrazolylacetic acid (TzAA). Testing of optimized CEZ synthesis using IECASA in a batch reactor has proved sufficiently high operational stability of the biocatalyst, with its residual activity after the 25th cycle accounting for about 83 ± 2% of its starting value. The half-inactivation period of IECASA was estimated as 85 cycles of CEZ synthesis.

[Recombinant cephalosporin-acid synthesase: optimisation of expression in E.coli cells, immobilisation and application for biocatalytic cefazolin synthesis].

Cephalosporin acid synthetase (CASA) is responsible for specific to synthesis of cephalosporin-acids, its expression in Escherichia coli cells is accompanied by accumulation of unprocessed insoluble precursor. In order to optimize conditions of recombinant CASA production we have studied the effects of several parameters of strain cultivation, including growth media composition, temperature, and inoculation dose. Also plasmids for production of CASA variants with the signal sequence of Erwinia carotovora L-asparaginase (ansCASA) and "leaderless" CASA were created in search of more efficient expression constructs. Removal of the N-terminal secretion signal sequence reduced the production of functionally active CASA more than 10-fold and inhibited strain growth. Insertion of the L-asparaginase signal sequence increased the specific enzyme activity in the resultant recombinant strain. The ansCASA producing strain was used to develop the method of immobilization of the recombinant enzyme on an epoxy-activated macroporous acrylic support. The resultant biocatalyst performed effective synthesis of cefazolin from 3-[(5-methyl-1,3,4-thiadiazol-2-il)-thiomethyl]-7- aminocephalosporanic acid (MMTD-7-ACA) and methyl ester of 1(H)-tetrazolilacetic acid (МETzAA), under mild conditions a transformation level of MMTD-7-ACA to cefazolin of 95% is reached.

[Morphofunctional changes in the heart, liver and skeletal muscles during temporary occlusion of the abdominal aorta]. / Morfofunktsional'nye izmeneniia serdtsa, pecheni i skeletnykh myshts pri vremennoi okkliuzii briushnoi aorty.

Experimental abdominal aorta ligation at the bifurcation site was performed in anesthetized mongrel dogs (body mass 12-17 kg) under controlled respiration. Aortic ligation produced a significant effect on the physiological indices of cardiac function, ultrastructure of the myocardium, liver and musculus quadriceps femoris, as well as on the content of macroergic compounds in these organs. One-hour aortic occlusion caused mainly reversible dystrophic changes in the tissues studied; 2-8-hour aortic ligation led to much more severe changes in the skeletal musculature, liver, and heart, while reperfusion, as a rule, impaired the cardiac and hepatic status. The latter may be attributed to the release of neuromediators and intermediate metabolism products from the ischemic skeletal muscles.

Venus: detailed mapping of maxwell montes region.

From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled.