Linked Life Data

9398172

Source:http://linkedlifedata.com/resource/pubmed/id/9398172

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
47
pubmed:dateCreated
1998-1-8
pubmed:abstractText
p-Nitrophenyl N-alkylcarbamates with different alkyl chains were used as substrates to determine separately the carbamylation and decarbamylation rates of the lipases from Staphylococcus hyicus and S. aureus. Both enzymes are reversibly inhibited by these compounds due to a rapid carbamylation of their active site serines followed by a slow decarbamylation. The carbamylation reaction is strongly pH-dependent and the pH profile suggests that an unprotonated histidine is required for this reaction. In contrast, the decarbamylation is pH-independent suggesting the presence of a hydrogen bond between the active site histidine and the carbamyl moiety. S. hyicus lipase preferably reacts with medium to long chain carbamates with an optimum for eight carbon atoms. In contrast, S. aureus lipase is highly specific for short chain carbamates. These results are in agreement with the respective substrate preferences of both lipases toward natural lipids. The decarbamylation rates of both enzymes hardly depend on the alkyl chain length, and from this it is concluded that chain length selectivity is expressed in the first step of catalysis. Both the carbamylation and decarbamylation reaction rates of S. hyicus lipase are enhanced in the presence of micelles, the activation effect being most pronounced in the first step. For the S. aureus lipase only a small influence of interfaces on both reaction steps was observed. These results are discussed in view of a possible role of a lid covering the active site. Kinetic experiments in the presence and absence of calcium strongly suggest that calcium ions are important for the structural stabilization of the unmodified as well as of the carbamylated enzymes. This structural function of calcium was supported by urea unfolding experiments, from which it appeared that for both enzymes the free energy for unfolding is significantly lower in the absence of calcium. In conclusion our results show that kinetic differences between both lipases reside in the acylation step, and that calcium is important for the structural stabilization of the unmodified, and moreover, the acylated enzymes.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
25
pubmed:volume
36
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
14539-50
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1997
pubmed:articleTitle
Dissecting the catalytic mechanism of staphylococcal lipases using carbamate substrates: chain length selectivity, interfacial activation, and cofactor dependence.
pubmed:affiliation
Department of Enzymology and Protein Engineering, CBLE, Utrecht University, The Netherlands.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't