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| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
19
|
| pubmed:dateCreated |
1980-11-24
|
| pubmed:abstractText |
When beta-glucosidase from sweet almonds reacts with p-nitrophenyl-beta-D-glucoside at subzero temperatures, a rapid release of p-nitrophenol, stoichiometric with enzyme concentration, occurs prior to turnover. This observation is interpreted as reflecting rapid formation of a glucose-enzyme intermediate, followed by rate-limiting breakdown. The energies of activation for the formation and breakdown of the intermediate were 6.0 +/- 2 and 19.0 +/- 2 kcal mol-1, respectively. Extrapolation of the reaction rates to higher temperatures suggests an isokinetic temperature circa 24 degrees C. Measurement of kcat in aqueous solution as a function of temperature yields a breakpoint in the Arrhenius plot at 20 degrees C and activation energies above and below this point which correspond to the values at subzero temperatures (6.7 and 17.0 kcal mol-1, respectively). This breakpoint thus reflects a change in the rate-determining step from formation of the intermediate at higher temperatures to breakdown at lower values, and explains why a "burst" of p-nitrophenol is observed at low, but not high, temperatures with this substrate. The significance of this finding to other glycohydrolases, and enzyme catalysis in general, is considered.
|
| pubmed:grant | |
| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:citationSubset |
IM
|
| pubmed:chemical | |
| pubmed:status |
MEDLINE
|
| pubmed:month |
Oct
|
| pubmed:issn |
0021-9258
|
| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:day |
10
|
| pubmed:volume |
255
|
| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
9030-2
|
| pubmed:dateRevised |
2007-11-14
|
| pubmed:meshHeading | |
| pubmed:year |
1980
|
| pubmed:articleTitle |
Temperature-dependent change in the rate-limiting step of beta-glucosidase catalysis.
|
| pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, P.H.S.
|