PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “modification”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed1977

Selective chemical modification of Escherichia coli elongation factor G: butanedione modification of an arginine essential for nucleotide binding.

Treatment of Escherichia coli elongation factor G with the arginine reagent, 2,3-butanedione, leads to the inactivation of the enzyme when performed in sodium borate buffers. The inhibition follows pseudo-first-order kinetics until 95% of the activity has been lost and further incubation results in complete inhibiton. Removal of the borate by exhaustive dialysis results in the restoration of approximately 85% of the original activity. The pH dependence of the reaction suggests that the ionization of a group in the protein with a pKa of approximately 8.8 facilitates the reaction with butanedione. A reaction order of 1.01 +/- 0.13 was calculated for the inhibition reaction, indicating that the incorporation of one butanedione per elongation factor G results in the inactivation of the enzyme. The kinetics of inhibition in the presence of GTP indicate that the elongation factor G-GTP complex is refractory to butanedione inhibiton. Elongation factor G which has been partially inactivated by butanedione has the same apparent Km for GTP as does the native enzyme. These results indicate that elongation factor G contains only one essential arginine residue which is reactive with butanedione and that this residue is located at its nucleotide binding site.

Butanones↗
PubMed2004

Structural modifications of plumieride isolated from Plumeria bicolor and the effect of these modifications on in vitro anticancer activity.

Plumieride was isolated as one of the major components from the biologically active methanolic extract of the bark of Plumeria bicolor (family Apocynaceae). For investigating the effect of substituents on cytotoxic activity it was modified into a series of compounds. Replacing the methyl ester functionality of plumieride with alkyl amides of variable carbon units improved the cytotoxic activity, and a correlation between overall lipophilicity and cytotoxic activity was observed. In plumieride, the glucose moiety was converted into a di- and trisaccharide by following the protection and deprotection approach, and the resulting compounds produced enhanced cytotoxicity. However, these compounds were found to be less effective than plumeiride containing a dodecyl (12 carbon units) amide group. Among all of the derivatives, the naturally occurring plumieride showed the least cytotoxicity (50% cell kill = 49.5 microg/mL), and the dodecyl amide analogue of plumieridepentaacetate produced the best efficacy (50% cell kill = 11.8 microg/mL). The di- and trisaccharide analogues were found to be slightly less effective than the dodecyl derivative (50% cell kill = 15-17 microg/mL). The in vitro cytotoxicity of the plumieride analogues was determined in radiation-induced fibrosarcoma (RIF) tumor cells.

Antineoplastic Agents↗
PubMed2001

Modification of surgical aortoatrial shunts for inaccessible bleeding in aortic surgery -- modification of the Cabrol-shunt technique.

Bleeding after complex ascending aortic, aortic root or transverse arch surgery which is inaccessible or difficult to control may present a major problem. Here, we describe a modified Cabrol-shunt technique using complete mediastinal coverage with decompression into the innominate vein where the classical technique is not suitable. The long-term fate of the classical aortoatrial and modified mediastinal to innominate shunts has been analyzed to assess their potential complications.

Aortic Aneurysm, Thoracic↗
PubMed1992

Cloning and sequence analysis of the StsI restriction-modification gene: presence of homology to FokI restriction-modification enzymes.

StsI endonuclease (R.StsI), a type IIs restriction endonuclease found in Streptococcus sanguis 54, recognizes the same sequence as FokI but cleaves at different positions. A DNA fragment that carried the genes for R.StsI and StsI methylase (M.StsI) was cloned from the chromosomal DNA of S.sanguis 54, and its nucleotide sequence was analyzed. The endonuclease gene was 1,806 bp long, corresponding to a protein of 602 amino acid residues (M(r) = 68,388), and the methylase gene was 1,959 bp long, corresponding to a protein of 653 amino acid residues (M(r) = 76,064). The assignment of the endonuclease gene was confirmed by analysis of the N-terminal amino acid sequence. Genes for the two proteins were in a tail-to-tail orientation, separated by a 131-nucleotide intercistronic region. The predicted amino acid sequences between the StsI system and the FokI system showed a 49% identity between the methylases and a 30% identity between the endonucleases. The sequence comparison of M.StsI with various methylases showed that the N-terminal half of M.StsI matches M.NIaIII, and the C-terminal half matches adenine methylases that recognize GATC and GATATC.

Amino Acid Sequence↗
PubMed1976

Studies of enzyme-catalyzed modification of proteins. I. Tyrosinase-catalyzed modification of asparaginase.

Asparaginase [EC 3.5.1.1.] of Escherichia coli, an anti-tumor enzyme, was inactivated in a time-dependent fashion by mushroom tyrosinase [EC1.14.18.1.]. The inactivation did not proceed, however, when heat-inactivated tyrosinase was used. Exculusion of the atmospheric oxygen or addition of diethyldithiocarbamate, a copper selective chelating agent, prevented the inactivation. The difference absorption spectrum of tyrosinase-inactivated asparaginase versus intact asparaginase exhibited the appearance of marked absorption peaks at 300 and 350 nm. These results indicate that the tyrosyl residue(s) of asparaginase, which is essential for the activity is enzymatically modified by tyrosianes.

Asparaginase↗
PubMed1990

Protein-polymer grafts, IV. A. Modification of amino acids: IIai. Modification of free lysine with reductive arylation.

Inability to increase the yield of reaction between 2,4 dihydroxybenzaldehyde and gelatin beyond 55 and 60% has led to an extensive investigation of reductive alkylation with free lysine. Even with free lysine, the extent of reaction was about 60%. Since this could be attributed to the electron donation by the phenolic hydroxyls, reductive alkylation was performed between o-, m-, and p-nitrobenzaldehydes and free lysine; o- and m-nitrobenzaldehyde were ineffective in increasing the yield while with p-nitrobenzaldehyde a yield of 72% was achieved. The unreacted 28% of the lysines are susceptible to epichlorohydrin. These results suggest that the slow, reversible first step in reductive alkylation, the formation of the Schiff's base, is responsible for the low yield.

Alkylation↗
PubMed1985

Spectinomycin modification. II. Spectinomycin C-3'-modification via diazoketone intermediates.

The C-3'-carbonyl group of N-protected spectinomycin is efficiently converted into a diazo group via base treatment of the corresponding tosylhydrazone. The diazo group imparts a new synthetically useful reactivity pattern on the sugar ring of the molecule. The synthesis of C-3'-deoxo-, monohalo- and dihalospectinomycins via the intermediacy of these diazo compounds is described. The reduced bioactivity of these analogs as compared to the parent and the C-3'-dihydro and aminospectinomycins established the need for hydrogen bonding groups in this region of the molecule for good activity, further refining the structure activity relationships in the spectinomycin series.

Chemical Phenomena↗