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91.
Mouse hybridoma cells cultured on the verge of starvation-induced apoptosis, i.e. in a medium diluted with saline, proved to serve as a sensitive screening system for apoptosis-suppressing activity of nutrient medium components. Conventional amino acid mixtures were found to suppress the starvation-induced apoptosis, whereas a vitamin mixture was ineffective. (Frank F (1995) Biotechnol. Bioeng. 45: 86–90). Recent experiments showed that suppression of apoptosis, and concurrent resumption of growth, could be achieved by addition of single substances at millimolar concentrations. The set of active substances included certain coded L-amino acids (glycine, alanine, serine, threonine, proline, asparagine, glutamine, histidine), non-coded amino acids (-alanine, taurine, 4-aminobutyric acid), and a non-metabolizable analogue (2-aminoisobutyric acid). This finding shows that some amino acids do not act solely as nutrients, but also as specific signal molecules. The specificity of the effect points to the involvement of adaptively regulated amino acid transport systems A and N in maintaining the balance between triggering and suppression of starvation-induced apoptosis. 相似文献
92.
D. Vandák M. Tomáška J. Zigová E. Šturdík 《World journal of microbiology & biotechnology》1995,11(3):363-363
Improved production of butyrate (up to 19 g/l) from whey by Clostridium butyricum was achieved by adding either yeast extract (5 g/l) or biotin (50 g/l). Hydrolysed lactose and proteolysed whey were less effective even with added biotin.The authors are with the Department of Biochemical Technology, Faculty of Chemical Technology, Slovak Technical University, Radlinského 9, Bratislava 812 37, Slovakia 相似文献
93.
94.
95.
The effect of ten derivatives of carbonylcyanide phenylhydrazone on growth of bacteria, yeast and different species of filamentous
fungi was investigated. In yeast and mitochondria isolated from rat liver the effect of these derivatives on the respiratory
activity was also followed. The relative efficiency of the individual derivatives of earbonylcyanide phenylhydrazone was determined
on the basis of the results obtained. It was shown that derivatives, in which the substituent on the benzene ring causes simultaneously
an increase of acidity and lipophilicity of the derivative as compared with the non-substituted carbonylcyanide phenylhydrazone
(4-trifluoromethoxy-, 3-chloro-, 4-chloro and 3,4-dichloroderivatives) were most effective. 相似文献
96.
M. Šlosárek 《Folia microbiologica》1977,22(4):262-268
It was the aim of the present communication to find a simple test for a reliable discrimination ofMycobacterium bovis BCG fromMycobacterium tuberculosis. A total of 26 BCG strains, out of them 10 Czechoslovak strains (2 lyophilized cultures of BCG of different batch, 6 strains
isolated from abscesses of children after BCG-vaccination and 2 strains from fatal cases after BCG-vaccination) and 16 strains
obtained from foreign laboratories, were used. Of the tested characteristics a combination of 3 tests, sensitivity to 1 μg
of 2-thiophene carbonylhydrazide (TCH), activity of 3 acylamidases (urease, nicotinamidase and pyrazinamidase) and a quantitative
nitrate test, was found to be most advantageous. The Czechoslovak strains ofMycobacterium bovis BCG were fully sensitive to TCH, of the 3 acylamidases mentioned above only urease was positive and nitrate was reduced only
little or not at all. On the other hand, strains ofMycobacterium tuberculosis were always resistant to TCH, had positive urease, nicotinamidase and pyrazinamidase and reduced nitrate very intensively. 相似文献
97.
An auxotrophic strain ofEscherichia coli with therecB recC sbcB genotype was transformed by chromosomal DNA of the prototrophic strain and by plasmid DNA carrying genes for antibiotic resistance
(R1drd 19). The donor plasmid DNA obtained by cell lysis in the presence of Triton X-100 and subsequent centrifugation in a caesium
chloride-ethidium bromide gradient was shown to have a circulaf molecule and to retain its completeness after penetration
into the recipient. Experiments with mixtures or plasmid and chromosomal DNA indicate a competition between these two DNA
types during the transformation reaction in the given system. 相似文献
98.
Winter rape ( Brassica napus L., var. olifera cv. Górczanski) seedlings were exposed to hardening conditions and the content and composition of free sterols as well as the ratio of free sterols to total phospholipids were determined. There was a reduction in free sterol content in the leaves at the most advanced stage of hardening. The ratio of free sterol to total phospholipids was significantly reduced by hardening due to a decrease in the level of the former and an increase in that of the latter compounds. There was a negative correlation between this ratio and the temperature at which half of the seedlings died. Thus, adaptation of membranes to temperature takes place also at the level of sterol-phospholipid interactions. Exposing seedlings already hardened to freezing temperatures caused injury higher than 50%, and brought about a drastic increase in the level of free sterols and an elevation in the ratio of free sterols to phospholipids. The results are discussed in terms of a possible role of the molecular architecture of membranes in surviving at subzero temperatures. 相似文献
99.
Two new recombinant haplotypes of the rat major histocompatibility system,RT1, have been detected in [LEW.1A (RT1
a
) ×LEW.1W (RT1
u
)] × LEW 1N(RT1
n
) segregating hybrids. Recombinantr3 carries theRTL1. A region (determining classical transplantation antigens) and theRT1.B region (determining strong mixed lymphocyte reactivity and genetic control of antipolypeptide immune responsiveness) of the RT1a parent, bur rejects RT1a skin grafts. Recombinantr4 carries theA andB regions of the RT1u parent, but rejects RT1u skin grafts. The two histocompatibility genes detected are allelic to each other. The relevant locus, designated asH-C, maps to theB-region side of theRT1 system and appears to mark a thirdRT1 gene region,RT1.C. Availability of haplotypes r3 andr4 allowed the definition of a histocompatibility locus in theB region,H-B. The products ofH-C, H-B and of the previously describedH-A gene vary in antigenic strength. 相似文献
100.
Vytas K. Švedas Alexei L. Margolin Ilya V. Berezin 《Enzyme and microbial technology》1980,2(2):138-144
The equilibrium constants and the respective standard Gibbs energy changes for hydrolysis of some β-lactam antibiotics have been determined. Native and immobilized penicillin amidase (EC 3.5.1.11) from Escherichia coli has been used as a catalyst. The values of standard Gibbs energy changes corresponding to the pH-independent product of equilibrium concentrations (ΔG0c = ? RT ln Kc) have been calculated. The differences in the structure of the antibiotics nucleus hardly ever affect the value of the pH-independent component of the standard Gibbs energy change (ΔG0c) and value of apparent standard Gibbs energy change at a fixed pH (ΔG0′c). At the same time, the value of ΔG0c is more sensitive to the structure of the acyl moiety of the antibiotic; when ampicillin is used instead of benzylpenicillin, ΔG0c increases by ~6.3 kJ mol?1 (1.5 kcal mol?1). pH-dependences of the apparent standard Gibbs energy changes for hydrolysis of β-lactam antibiotics have been calculated. The pH-dependences of ΔG0′c for hydrolysis of all β-lactam antibiotics have a similar pattern. The thermodynamic pH optimum of the synthesis of these compounds is in the acid pH range (pH < 5.0). The breakage of the β-lactam ring leads to a sharp decrease in the ΔG0′c value and a change in the pattern of the pH-dependence. For example, at pH 5.0 ΔG0′c decreases from 14.4 kJ mol?1 for benzylpenicillin to ?1.45 kJ mol?1 for benzylpenicilloic acid. The reason for these changes is mainly a considerable increase in the pK of the amino group of the nucleus of the antibiotic and, as a consequence, a decrease in the component of standard Gibbs energy change, corresponding to the ionization of the system. The thermodynamic potentials of the enzymatic synthesis of semisynthetic penicillins and cephalosporins on the basis of both free acids and their derivatives (N-acylated amino acids, esters) are discussed. It is shown that with esters of the acids, a high yield of the antibiotic can, in principle, be achieved at higher pH values. 相似文献