The mechanism of action of β-galactosidase Effect of aglycone nature and α-deuterium substitution on the hydrolysis of aryl galactosides

1975 ◽  
Vol 145 (3) ◽  
pp. 417.b1-417.b1
Author(s):  
M. L. Sinnott ◽  
I. J. L. Souchard
Keyword(s):  
Mechanism Of Action ◽  
Deuterium Substitution ◽  
Hydrolysis Of

Insights into chaperonin function from studies on archaeal thermosomes

2011 ◽  
Vol 39 (1) ◽  
pp. 94-98 ◽  
Author(s):  
Peter Lund
Keyword(s):  
Cell Death ◽  
Protein Folding ◽  
Recent Work ◽  
Mechanism Of Action ◽  
Molecular Chaperones ◽  
Short Review ◽  
Living Cells ◽  
Living Organisms ◽  
Opening And Closing ◽  
Hydrolysis Of

It is now well understood that, although proteins fold spontaneously (in a thermodynamic sense), many nevertheless require the assistance of helpers called molecular chaperones to reach their correct and active folded state in living cells. This is because the pathways of protein folding are full of traps for the unwary: the forces that drive proteins into their folded states can also drive them into insoluble aggregates, and, particularly when cells are stressed, this can lead, without prevention or correction, to cell death. The chaperonins are a family of molecular chaperones, practically ubiquitous in all living organisms, which possess a remarkable structure and mechanism of action. They act as nanoboxes in which proteins can fold, isolated from their environment and from other partners with which they might, with potentially deleterious consequences, interact. The opening and closing of these boxes is timed by the binding and hydrolysis of ATP. The chaperonins which are found in bacteria are extremely well characterized, and, although those found in archaea (also known as thermosomes) and eukaryotes have received less attention, our understanding of these proteins is constantly improving. This short review will summarize what we know about chaperonin function in the cell from studies on the archaeal chaperonins, and show how recent work is improving our understanding of this essential class of molecular chaperones.

Jack bean urease (EC 3.5.1.5). V. On the mechanism of action of urease on urea, formamide, acetamide, N-methylurea, and related compounds

1980 ◽  
Vol 58 (12) ◽  
pp. 1335-1344 ◽  
Author(s):  
Nicholas E. Dixon ◽  
Peter W. Riddles ◽  
Carlo Gazzola ◽  
Robert L. Blakeley ◽  
Burt Zerner
Keyword(s):  
Enzymatic Hydrolysis ◽  
Mechanism Of Action ◽  
Active Site ◽  
Ph Dependence ◽  
Jack Bean Urease ◽  
Nickel Ion ◽  
Jack Bean ◽  
First Time ◽  
Hydrolysis Of ◽  
Hydrolysis Of Urea

Acetamide and N-methylurea have been shown for the first time to be substrates for jack bean urease. In the enzymatic hydrolysis of urea, formamide, acetamide, and N-methylurea at pH 7.0 and 38 °C, kcat has the values 5870, 85, 0.55, and 0.075 s−1, respectively. The urease-catalyzed hydrolysis of all these substrates involves the active-site nickel ion(s). Enzymatic hydrolysis of the following compounds could not be detected: phenyl formate, p-nitroformanilide, trifluoroacetamide, p-nitrophenyl carbamate, thiourea, and O-methylisouronium ion. In the enzymatic hydrolysis of urea, the pH dependence of kcat between pH 3.4 and 7.8 indicates that at least two prototropic forms are active. Enzymatic hydrolysis of urea in the presence of methanol gave no detectable methyl carbamate. A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently an O-bonded carbamato–enzyme intermediate.

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