Increased stability and catalytic efficiency of yeast hexokinase upon interaction with zwitterionic micelles. Kinetics and conformational studies.
The effect of ligands (glucose, ATP and Mg2+) and zwitterionic micelles of lysophosphatidylcholine (LPC) or N-hexadecyl-N,N-dimethyl-3-ammonium propanesulfonate (HPS) in the yeast hexokinase (HK) stability was studied at 35 degrees C. The thermal inactivation kinetics followed one-exponential decay. The effect of ligands on protecting the enzyme against inactivation followed the order: glucose > glucose/Mg2+ >ATP/Mg2+ approximately or approximately equal to Mg2+l approximately or approximately equal to buffer only. Both LPC and HPS micelles increased the enzyme stability only when the incubation medium contained glucose or glucose/Mg2+, suggesting that the protein conformation is a key prerequisite for the enzyme-micelle interaction to take place. This enzyme-micelle interaction resulted in an increased catalytic efficiency (with a decrease in Km for ATP and increase in Vmax as well as in changes on the tertiary (intrinsic fluorescence) structure of the yeast hexokinase.
Guerra
R
R
Departamento de Bioquímica Médica, ICB/CCS, Universidade Federal do Rio de Janeiro, CEP, Brazil.
Bianconi
M L
ML
D000255:Adenosine Triphosphate / Q000737:chemistry; D002384:Catalysis; D005947:Glucose / Q000737:chemistry; D006593:Hexokinase / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008274:Magnesium / Q000737:chemistry; D008823:Micelles; D011485:Protein Binding; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors; D015003:Yeasts / Q000201:enzymology*
D008024:Ligands; D008244:Lysophosphatidylcholines; D008823:Micelles; C094641:N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D000255:Adenosine Triphosphate; D006593:Hexokinase; D008274:Magnesium; D005947:Glucose