scholarly journals The role of histidine residues in glutamate dehydrogenase

1972 ◽  
Vol 129 (2) ◽  
pp. 419-425 ◽  
Author(s):  
N. Tudball ◽  
R. Bailey-Wood ◽  
P. Thomas
Keyword(s):  
Enzyme Activity ◽  
Glutamate Dehydrogenase ◽  
Rose Bengal ◽  
Marked Decrease ◽  
Total Loss ◽  
Appreciable Effect ◽  
Normal Response ◽  
Original Activity ◽  
Histidine Residues

1. Glutamate dehydrogenase was subject to rapid inactivation when irradiated in the presence of Rose Bengal or incubated in the presence of ethoxyformic anhydride. 2. Inactivation in the presence of Rose Bengal led to the photo-oxidation of four histidine residues. Oxidation of three histidine residues had little effect on enzyme activity, but oxidation of the fourth residue led to the almost total loss of activity. 3. Acylation of glutamate dehydrogenase with ethoxyformic anhydride at pH6.1 led to the modification of three histidine residues with a corresponding loss of half the original activity. Acylation at pH7.5 led to the modification of two histidine residues and a total loss of enzyme activity. 4. One of the histidine residues undergoing reaction at pH6.1 also undergoes reaction at pH7.5. 5. The presence of either glutamate or NAD+in the reaction mixtures at pH6.1 had no appreciable effect. At pH7.5 glutamate caused a marked decrease in both the degree of alkylation and degree of inactivation. NAD+had no effect on the degree of inactivation at pH7.5 but did modify the extent of acylation. 6. The normal response of the enzyme towards ADP was unaffected by acylation at pH6.1 or 7.5. 7. The normal response of the enzyme towards GTP was altered by treatment at both pH6.1 and 7.5.

Stabilization of papain from papaya peels / Estabilización de la papaína de la cáscara de papaya

1998 ◽  
Vol 4 (3) ◽  
pp. 179-187 ◽  
Author(s):  
N. Espin ◽  
M.N. Islam
Keyword(s):  
Ascorbic Acid ◽  
Enzyme Activity ◽  
Protective Effect ◽  
Total Concentration ◽  
Sodium Ascorbate ◽  
Sodium Metabisulfite ◽  
Appreciable Effect ◽  
Original Activity ◽  
Before And After ◽  
Erythorbic Acid

Crude papain in papaya peels was stabilized before drying by the addition of various chemicals (ascorbic acid, sodium ascorbate, erythorbic acid, sodium erythorbate, sodium metabisulfite, sodium tetrathionate, 4-hexylresorcinol, t-butyl hydroquinone [TBHQ], rutin, α-tocopherol, trehalose, and sucrose). Chemicals were added to the ground papaya peels at 0, 0.12, 0.25, 0.5, 0.75, 1, 1.25, and 1.5% (w /w). Drying temperatures were 40, 55 and 60 °C. Enzyme activity was measured before and after drying by the casein digestion method. Percentage of enzyme activity retained (% EAR) was calculated by assigning a value of 100% EAR to fresh peels. Possible synergism between chemicals was also studied for a 1:1 ratio chemical/chemical at 1% total concentration. The highest % EAR was obtained at 55 °C for all chemicals except for sucrose and trehalose which showed their best effect at 40 °C. TBHQ rutin, α-tocopherol and 4-hexylresorcinol showed a destabilizing effect. Maximum protective effect occurred at 1% concentration. At this concentration sodium tetrathionate showed the best protective effect (90% EAR) followed by sodium metabisulfite (85% EAR), while both sodium ascorbate and sodium erythorbate retained 75% of the original activity. Ascorbic acid and erythorbic acid were 10% less effective than their corresponding sodium salts, possibly due to lower pH. Trehalose showed only 57 % EAR while sucrose failed to produce any appreciable effect. No synergistic effect was shown by any combination of chemicals.

scholarly journals Mutations within a highly conserved sequence present in the X region of phosphoinositide-specific phospholipase C-δ1

1995 ◽  
Vol 307 (1) ◽  
pp. 69-75 ◽  
Author(s):  
M V Ellis ◽  
U Sally ◽  
M Katan
Keyword(s):  
Enzyme Activity ◽  
Phospholipase C ◽  
Limited Proteolysis ◽  
Structural Similarity ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Histidine Residues ◽  
Conserved Sequence ◽  
Hydrolysis Of

Phosphoinositide-specific phospholipase C (PI-PLC) enzymes have considerable structural similarity within limited regions (X and Y) implicated in catalysis. The role of residues contained within a highly conserved sequence present in the X region was investigated by site-directed mutagenesis of PLC-delta 1 isoenzyme. Seven residues (Ser-308, Ser-309, Ser-310, His-311, Thr-313, Tyr-314, and Gln-319) were individually replaced by alanine or glutamine (His-311). Replacement of two residues, His-311 and Tyr-314, resulted in a dramatic reduction of enzyme activity. The kcat of hydrolysis of phosphatidylinositol 4,5-bisphosphate by H311A and Y314A mutants was reduced 1000- and 10-fold respectively, with little effect on Km. Further analysis of H311A and Y314A mutants, using limited proteolysis and circular dichroism, had shown that no major structural alterations had occurred. Since site-directed mutagenesis demonstrated the importance of histidine residues, their role in enzyme function was also analysed by chemical modification with diethyl pyrocarbonate. This modification of histidine residues resulted in the reduction of enzyme activity and also indicated that more than one residue could be important.

A possible role of arginase in the regulation of polyamine biosynthesis in the rat thyroid

1981 ◽  
Vol 98 (1) ◽  
pp. 57-61 ◽  
Author(s):  
Shigeru Matsuzaki ◽  
Mitsuo Suzuki ◽  
Koei Hamana
Keyword(s):  
Amino Acids ◽  
Enzyme Activity ◽  
Arginase Activity ◽  
Polyamine Biosynthesis ◽  
Rat Thyroid ◽  
Arginine Concentration

Abstract. Effect of chronic methylthiouracil (MTU) treatment on the thyroid arginase activity and thyroidal concentration of arginine, ornithine and other amino acids was studied in the rat. The activity of thyroid arginase increased significantly at 15 days of MTU treatment and the elevated enzyme activity was reduced to normal by l-thyroxine (T4) injection. The thyroidal concentration of polyamines was increased by MTU and decreased by T4 with the exception of spermine. The thyroidal concentration of arginine and lysine, a substrate and an inhibitor for arginase respectively decreased significantly, while that of ornithine remained unchanged after MTU treatment. T4 injected to MTU-pretreated rats restored the decreased arginine concentration to normal. These results suggest that ornithine supply for polyamine biosynthesis is regulated by the level of both arginase and lysine in the thyroid.

Protective role of Bacopa monniera on morphine-induced brain mitochondrial enzyme activity in rats

Fitoterapia ◽  
2002 ◽  
Vol 73 (5) ◽  
pp. 381-385 ◽  
Author(s):  
T. Sumathy ◽  
S. Govindasamy ◽  
K. Balakrishna ◽  
G. Veluchamy
Keyword(s):  
Enzyme Activity ◽  
Protective Role ◽  
Mitochondrial Enzyme ◽  
Bacopa Monniera
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