Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
3
pubmed:dateCreated
1972-12-26
pubmed:abstractText
alpha-Isopropylmalate synthase, the first specific enzyme in leucine biosynthesis, was purified approximately 100-fold from extracts of Saccharomyces sp. (strain 60615), the most effective step being specific elution with the feedback inhibitor leucine from a hydroxyapatite column. In the early steps of purification, special care was taken to protect the synthase against proteolytic activities. The apparent molecular weight of the enzyme as determined from gel filtration on a calibrated column was 137,000 in the absence and 121,000 in the presence of leucine. Inhibition by leucine was specific and strongly pH-dependent, with the leucine concentration necessary for half-maximal inhibition increasing about 10-fold as the pH increased from 7.5 to 8.5. Within this pH range, catalytic activity remained almost unchanged. The apparent K(m) values for the two substrates were found to be 16 mum for alpha-ketoisovalerate and 9 mum for acetyl-coenzyme A. K(+) was required for full activity, the apparent K(a) value being 2 mm. Leucine inhibition was of the mixed type, resulting in decreased V(max) and increased apparent K(m) values forboth substrates. Whereas no cooperative effects were observed with either substrate, positive cooperativity was seen with leucine in the presence of saturating substrate concentrations. Leucine and, to a lesser extent, alpha-ketoisovalerate stabilized the purified enzyme against heat-inactivation. The presence of acetyl-coenzyme A, on the other hand, accelerated the inactivation. In subsequent experiments, coenzyme A was recognized as the actual inactivating ligand, being effective even at lower temperatures and in concentrations which were estimated to be in the range of the enzyme concentration.
pubmed:commentsCorrections
http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-13522725, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-14087358, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-4912200, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-4935285, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-4943789, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-4947783, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-4976555, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5484465, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5500946, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5724969, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5724970, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5783835, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5784215, http://linkedlifedata.com/resource/pubmed/commentcorrection/5079061-5966527
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
0021-9193
pubmed:author
pubmed:issnType
Print
pubmed:volume
110
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1118-26
pubmed:dateRevised
2009-11-19
pubmed:meshHeading
pubmed-meshheading:5079061-Acyltransferases, pubmed-meshheading:5079061-Cell Fractionation, pubmed-meshheading:5079061-Chemical Precipitation, pubmed-meshheading:5079061-Chromatography, pubmed-meshheading:5079061-Chromatography, Gel, pubmed-meshheading:5079061-Coenzyme A, pubmed-meshheading:5079061-Dicarboxylic Acids, pubmed-meshheading:5079061-Enzyme Activation, pubmed-meshheading:5079061-Feedback, pubmed-meshheading:5079061-Glycols, pubmed-meshheading:5079061-Hot Temperature, pubmed-meshheading:5079061-Hydrogen-Ion Concentration, pubmed-meshheading:5079061-Hydroxyapatites, pubmed-meshheading:5079061-Keto Acids, pubmed-meshheading:5079061-Kinetics, pubmed-meshheading:5079061-Leucine, pubmed-meshheading:5079061-Molecular Weight, pubmed-meshheading:5079061-Saccharomyces, pubmed-meshheading:5079061-Streptomycin, pubmed-meshheading:5079061-Sulfates, pubmed-meshheading:5079061-Valerates
pubmed:year
1972
pubmed:articleTitle
Alpha-isopropylmalate synthase from yeast: purification, kinetic studies, and effect of ligands on stability.
pubmed:publicationType
Journal Article