Identification of the rate-limiting step in the chymotrypsin-catalyzed hydrolysis of N-acetyl-L-tryptophanamide

1970 ◽  
Vol 92 (20) ◽  
pp. 6089-6090 ◽  
Author(s):  
Marion H. O'Leary ◽  
Michael D. Kluetz
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Hydrolysis Of

Biological treatability of a corn wet mill effluent

2002 ◽  
Vol 45 (12) ◽  
pp. 339-346 ◽  
Author(s):  
G. Eremektar ◽  
O. Karahan-Gul ◽  
F. Germirli-Babuna ◽  
S. Ovez ◽  
H. Uner ◽  
...  
Keyword(s):  
Biological Treatment ◽  
Rate Coefficient ◽  
Activated Sludge Process ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Metabolic Products ◽  
High Level ◽  
Biological Treatability ◽  
Rate Limiting ◽  
Hydrolysis Of

Corn wet mill effluents are studied in terms of their characteristics relevant for biological treatment. They have a high COD of mainly soluble and biodegradable nature, with practically no soluble inert components. They generate a relatively high level of soluble residual metabolic products, which affects the choice of the appropriate biological treatment and favors aerobic activated sludge process. Experimental assessment of process kinetics yields typical values. Hydrolysis of the slowly biodegradable COD, the rate limiting step for the utilization of substrate, is characterized by an overall rate coefficient, which is within the range commonly associated for the hydrolysis of starch.

Evidence for a solvent-induced change in rate-limiting step in the hydrolysis of benzaldehyde dimethyl acetal

1980 ◽  
Vol 102 (20) ◽  
pp. 6268-6271 ◽  
Author(s):  
Paul R. Young ◽  
Roy C. Bogseth ◽  
Edward G. Rietz
Keyword(s):  
Dimethyl Acetal ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Hydrolysis Of

scholarly journals Role of Asp104 in the SHV β-Lactamase

2006 ◽  
Vol 50 (12) ◽  
pp. 4124-4131 ◽  
Author(s):  
Christopher R. Bethel ◽  
Andrea M. Hujer ◽  
Kristine M. Hujer ◽  
Jodi M. Thomson ◽  
Mark W. Ruszczycky ◽  
...  
Keyword(s):  
Amino Acid ◽  
Catalytic Efficiency ◽  
Saturation Mutagenesis ◽  
Amino Acid Residues ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Threefold Increase ◽  
Rate Limiting ◽  
Hydrolysis Of

ABSTRACT Among the TEM-type extended-spectrum β-lactamases (ESBLs), an amino acid change at Ambler position 104 (Glu to Lys) results in increased resistance to ceftazidime and cefotaxime when found with other substitutions (e.g., Gly238Ser and Arg164Ser). To examine the role of Asp104 in SHV β-lactamases, site saturation mutagenesis was performed. Our goal was to investigate the properties of amino acid residues at this position that affect resistance to penicillins and oxyimino-cephalosporins. Unexpectedly, 58% of amino acid variants at position 104 in SHV expressed in Escherichia coli DH10B resulted in β-lactamases with lowered resistance to ampicillin. In contrast, increased resistance to cefotaxime was demonstrated only for the Asp104Arg and Asp104Lys β-lactamases. When all 19 substitutions were introduced into the SHV-2 (Gly238Ser) ESBL, the most significant increases in cefotaxime and ceftazidime resistance were noted for both the doubly substituted Asp104Lys Gly238Ser and the doubly substituted Asp104Arg Gly238Ser β-lactamases. Correspondingly, the overall catalytic efficiency (k cat/Km ) of hydrolysis for cefotaxime was increased from 0.60 ± 0.07 μM−1 s−1 (mean ± standard deviation) for Gly238Ser to 1.70 ± 0.01 μM−1 s−1 for the Asp104Lys and Gly238Ser β-lactamase (threefold increase). We also showed that (i) k 3 was the rate-limiting step for the hydrolysis of cefotaxime by Asp104Lys, (ii) the Km for cefotaxime of the doubly substituted Asp104Lys Gly238Ser variant approached that of the Gly238Ser β-lactamase as pH increased, and (iii) Lys at position 104 functions in an energetically additive manner with the Gly238Ser substitution to enhance catalysis of cephalothin. Based on this analysis, we propose that the amino acid at Ambler position 104 in SHV-1 β-lactamase plays a major role in substrate binding and recognition of oxyimino-cephalosporins and influences the interactions of Tyr105 with penicillins.

The Meyer Reaction of Phenylnitromethane in Acid. III. The Tautomerization to the aci-Form

1971 ◽  
Vol 49 (21) ◽  
pp. 3493-3501 ◽  
Author(s):  
J. T. Edward ◽  
P. H. Tremaine
Keyword(s):  
Rate Increase ◽  
Isotope Effects ◽  
Dilute Acid ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Deuterium Isotope Effects ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Competing Reactions

The rate-acidity profiles for the Meyer rearrangement–hydrolysis of phenylnitromethane in sulfuric, perchloric, and hydrochloric acid show a maximum near 3 M acid. Ring-substituted phenylnitromethanes also show a maximum in their rate profiles, at slightly different acid concentrations. These maxima arise because the slow formation of the aci-form is followed by two competing reactions: fast tautomerization back to the nitro-form, and fast rearrangement–hydrolysis to the Meyer products. The rearrangement is rate-limiting in dilute acid and is acid-catalyzed, causing the rate increase. In more concentrated acid, the rate-limiting step is the nitro to aci tautomerization, which is not acid-catalyzed, and which goes more slowly as the activity of water decreases.The tautomerization was studied by means of primary and solvent deuterium isotope effects, and was found to occur through proton abstraction by water, through a transition state closely resembling the products.

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