scholarly journals Chemical modification of barley malt α-amylase 2: Involvement of tryptophan and tyrosine residues in enzyme activity

1986 ◽  
Vol 51 (5) ◽  
pp. 295-308 ◽  
Author(s):  
Richard M. Gibson ◽  
Birte Svensson
Keyword(s):  
Enzyme Activity ◽  
Chemical Modification ◽  
Barley Malt ◽  
Tyrosine Residues

Chemical Modification of Human Lysozyme. Acetylation and Nitration of Tyrosine

1971 ◽  
Vol 49 (7) ◽  
pp. 816-821 ◽  
Author(s):  
R. L. Fawcett ◽  
T. J. Limbird ◽  
Sandra L. Oliver ◽  
C. L. Borders Jr.
Keyword(s):  
Enzyme Activity ◽  
Chemical Modification ◽  
Gel Filtration ◽  
Degree Of Polymerization ◽  
Tyrosine Residue ◽  
Amino Groups ◽  
Human Lysozyme ◽  
Tyrosine Residues ◽  
Typical Experiment ◽  
High Degree

When human lysozyme is reacted with a 60 M excess of N-acetylimidazole, only one of six tyrosine residues and two amino groups are acetylated. The acetylated lysozyme is 1.2 times as active towards M. lysodeikticus as the unmodified enzyme. When human lysozyme is reacted with a 4 M excess of tetranitromethane, approximately one tyrosine is nitrated. The tetranitromethane also simultaneously induces a high degree of polymerization of the lysozyme. In a typical experiment, nitration leads to a polymerized product that has only 25% of the activity of unmodified enzyme towards M. lysodeikticus. The polymerized lysozyme can be separated into several components by gel filtration on Sephadex G-75. Enzyme activity analyses of the chromatographed lysozyme oligomers indicate that tetranitromethane reduces the activity of human lysozyme primarily by polymerization, since the lysozyme monomer, which contains one nitrotyrosine per molecule, has 65% activity while the trimer has only 5% activity. N-Acetylglucosamine, N,N′-diacetylchitobiose, and N,N',N″-triacetylchitotriose, all inhibitors or substrates of human lysozyme, prevent neither the nitration of the single tyrosine residue nor the polymerization due to tetranitromethane action.

Site-Selective Protein Chemical Modification of Exposed Tyrosine Residues Using Tyrosine Click Reaction

2020 ◽  
Vol 31 (5) ◽  
pp. 1417-1424 ◽  
Author(s):  
Shinichi Sato ◽  
Masaki Matsumura ◽  
Tetsuya Kadonosono ◽  
Satoshi Abe ◽  
Takafumi Ueno ◽  
...  
Keyword(s):  
Chemical Modification ◽  
Click Reaction ◽  
Tyrosine Residues ◽  
Site Selective

Effect Of pH On The Stability And Conformation Of α-Thrombin

1981 ◽  
Author(s):  
German B Villanueva
Keyword(s):  
Chemical Modification ◽  
Structural Changes ◽  
Low Ph ◽  
Tryptophan Residue ◽  
Difference Spectroscopy ◽  
Compact Structure ◽  
Tyrosine Residues ◽  
Charge Interaction ◽  
The Stability ◽  
Peptide Region

It is known that storage at pH 6 stabilizes thrombin against inactivation. In order to determine whether structural changes accompany this stabilization, the conformation of human α-thrombin at pH 6.0 and 7.5 was investigated by chemical modification, solvent perturbation, UV difference spectroscopy and circular dichroism. It was shown that the CD spectra of α-thrombin at 230-200 nm peptide region were indistinguishable at two pH values indicating no difference in the secondary structure. However, differences were observed in the 320-250 nm aromatic region suggesting some changes in the microenvironment of the aromatic chromophores. Solvent perturbation in 20% ethylene glycol indicated 3.7 ± 0.5 Trp and 7.8 ± 0.5 Tyr were exposed to the solvent at pH 6.0 while 4.3 ± 0.4 Trp and 8.4 ± 0.5 Tyr were exposed at pH 7.5. Chemical modification of tryptophan residue by dimethyl(2-hydroxy- 5-nitrobenzyl)sulfonium bromide in a 100-fold molar excess of the reagent showed 3 reactive residues at pH 6.0 and 6 at pH 7.5. These results suggest that when thrombin is exposed to low pH, structural changes occur that decrease the relative degree of exposure of tryptophan and tyrosine residues. Furthermore, UV difference spectroscopy showed the development of a positive differential spectrum when thrombin at pH 6.0 was exposed to pH 7.5. From this study, it is concluded that the stability of thrombin at pH 6.0 is due to a more compact structure of the enzyme which is probably a result of reduced charge interaction at low pH.

Essential Arginine Residues in Lactate Dehydrogenase from Germinating Soybean

1994 ◽  
Vol 59 (2) ◽  
pp. 467-472 ◽  
Author(s):  
Jana Barthová ◽  
Irena Hulová ◽  
Miroslava Birčáková
Keyword(s):  
Enzyme Activity ◽  
Glycine Max ◽  
Lactate Dehydrogenase ◽  
Chemical Modification ◽  
Active Site ◽  
Enzyme Modification ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Arginine Residues ◽  
Blue Sepharose

The lactate dehydrogenase was isolated from soybean (Glycine max. L.) by a procedure that employed biospecific chromatography on a column of Blue-Sepharose CL-6B. The participation of the guanidine group of arginine residues in the mechanism of enzyme action was determined through kinetic and chemical modification studies. The dependence of enzyme activity on pH was followed in the alkaline region (pH 8.6 - 12.8). The pK values found were 12.4 for the enzyme substrate complex and 11.1 for the free enzyme. The enzyme was inactivated by phenylglyoxal, 2,3-butanedione, 1,2-cyclohexanedione and p-hydroxyphenylglyoxal reagents used in modification experiments. Kinetic analysis of the modification indicated that one arginine residue is modified when inactivation occurs. No effect was observed on the rate of inactivation upon addition of coenzyme. The extent of enzyme modification by p-hydroxyphenylglyoxal was determined. It appears there are at least two arginine residues in the active site of the enzyme.

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