[Enzymatic synthesis of 3,4-dihydroxyphenyl-L-alanine by free and immobilized Citrobacter freundii cells]. / Fermentativnyi sintez 3,4-dioksifenil-L-alanina svobodnymi i immobilizovannymi kletkami Citrobacter freundii.

The Citrobacter freundii 62 cells immobilized in PAAG and possessing the tyrosine-phenol-lyase (TPL) activity catalyse the synthesis of 3,4-dihydroxyphenyl-L-alanine (DOPA) from pyrocatechol and ammonium pyruvate. The synthesis of DOPA was studied using both free and immobilized bacterial cells. When the concentration of pyrocatechol is over 0.1 M the TPL activity of the cells is inhibited. The concentration of pyrocatechol can be increased up to 0.3 M by using an equimolar mixture of pyrocatechol and boric acid. The addition of ascorbic acid as an antioxidant results in a lower TPL activity of both free and immobilized bacterial cells.

[Study methods for localizing enzymes in the cells of gram-negative bacteria (a review)]. / Metody issledovaniia lokalizatsii fermentov v kletkakh gramotritsatel'nykh bakterii (obzor).

The present review systematizes the literature data on localization of enzymes in cells of Gram-negative bacteria. It centres round the methods used for studying the enzyme localization. The criteria according to which one can locate an enzyme in bacterial cells are discussed.

[Immobilization of Citrobacter freundii cells with tyrosine phenol-lyase activity by entrapment in natural gels]. / Immobilizatsiia kletok Citrobacter freundii s tiroz-infenol-liaznoi aktivnost'iu metodom vkliucheniia v prirodnye geli.

A comparative study on immobilization of Citrobacter freundii cells by entrapment in carrageenan, agar, agar-agar, and gelatin gels (5, 10, and 15%) was carried out. Gelatin gels were treated with glutaraldehyde to make them more rigid. As a result, the tyrosine phenol-lyase activity of these samples was less than that of free cells (about 40%). The yield of TP-lyase activity was 40--60% when cells were immobilized in 5% and 7% agar and agar-agar gels. The cells entrapped in carrageenan gels, the concentration of which was varied from 2 to 10%, possessed the highest tyrosine phenol-lyase activity (up to 90%). The efficiency of cell entrapment was high for all the carrier and equal to 70--90%. The plastic strength and swelling of the above gels, as well as the phenol adsorption on the carriers and the release of the bacterial cells from them were studied under the conditions of tyrosine phenol-lyase reaction.

[Isolation, purification and some properties of tyrosine-phenol-lyase from Citrobacter freundii cells]. / Vydelenie, ochistka i nekotorye svoistva tirozin-fenol-liazy iz kletok Citrobacter freundii.

A new procedure for isolation of tyrosine-phenol-lyase from the cells of C. freundii strain 62 allowing to obtain a highly purified enzyme with a high yield at a reduced time expenditure has been developed. The procedure described differs from the well-known method for isolation of the enzyme from the cells of Escherichia intermedia and Erwinia herbicola. Some properties of the enzyme from C. freundii 62, e.g. stability, dependence of the enzyme activity on some mono- and bivalent cations and pH- and temperature dependences of the enzyme have been studied. It was shown that the enzyme is activated by NH4+, K+, Na+ and is inhibited by Ca2+, Cu2+ and Mg2+. The enzyme loses up to 50% of its activity upon storage in glycerol with 2-mercaptoethanol during 1,5 months at -18 degrees.