Linked Life Data

9985

Source:http://linkedlifedata.com/resource/pubmed/id/9985

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
21
pubmed:dateCreated
1976-12-30
pubmed:abstractText
The binding of reduced nicotinamide adenine dinucleotide phosphate (NADPH) to nicotinamide adenine dinucleotide phosphate (NADP) dependent isocitrate dehydrogenase from beef liver cytoplasm was studied by several equilibrium techniques (ultracentrifugation, molecular sieving, ultrafiltration, fluorescence). Two binding sites (per dimeric enzyme molecule) were found with slightly different dissociation constants (0.5 and 0.12 muM) and fluorescence yields (7.7 and 6.3). A ternary complex was formed between enzyme, isocitrate, and NADPH, in which NADPH dissociation constant was 5 muM. On the contrary, no binding of NADPH to the enzyme took place in the presence of magnesium isocitrate. Dialysis experiments showed the existence of 1 NADP binding site/dimer, with a dissociation constant of 26 muM. When NADPH was present with the enzyme in the proportion of 1 molecule/dimer, the dissociation constant of NADP was decreased fourfold, reaching a value quantitatively comparable to the Michaelis constant. The kinetics of coenzyme binding was followed using the stopped-flow technique with fluorescence detection. NADPH binding to the enzyme occurred through one fast reaction (k1 = 20 muM-1 s-1). Dissociation of NADPH took place upon NADP binding; however, equilibrium as well as kinetic data were incompatible with a simple competition scheme. Dissociation of NADPH from the enzyme upon magnesium isocitrate binding was preceded by the formation of a transitory ternary complex in which the fluorescence of NADPH was only about 30% of that in the enzyme-NADPH complex. Then interaction between the conenzymes and the involvement of ternary complexes in the catalytic mechanism are discussed in relation with what is known about the regulatory role of the coenzyme (Carlier, M. F., and Pantaloni, D. (1976), Biochemistry, 15, 1761-1766).
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Oct
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
19
pubmed:volume
15
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
4703-12
pubmed:dateRevised
2009-10-27
pubmed:meshHeading
pubmed:year
1976
pubmed:articleTitle
Coenzyme binding by triphosphopyridine nucleotide dependent isocitrate dehydrogenase from beef liver. Equilibrium and kinetics studies.
pubmed:publicationType
Journal Article