Glucose binding isotope effects in the ternary complex of brain hexokinase demonstrate partial relief of ground-state destabilization.
Isotope effects can yield detailed information about contacts made between a bound compound and its host receptor or enzyme. In this study, we have measured isotope effects upon the equilibrium constant for the association of glucose and human brain hexokinase [E.C.2.7.1.1] in the presence of beta,gamma-CH(2)-ATP and compared these with data for the same equilibrium in the absence of ATP-analogue. We have found isotope effects of 1.012, 0.929, 1.031, 1.052, 0.998, and 1.032 for the competitive binding of [1-(3)H]-, [2-(3)H]-, [3-(3)H]-, [4-(3)H]-, [5-(3)H]-, or [6,6-(3)H(2)]- and either [2-(14)C]- or [6-(14)C]glucose to brain hexokinase. We observed changes only at H1, H5, and H6, and we attribute these to a slight change in the position of Asn683 and Glu742 due to nucleotide binding and to partial satisfaction of activated OH6 by the terminal nucleotide phosphorus.
Lewis
Brett E
BE
Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Schramm
Vern L
VL
D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000737:chemistry; D001921:Brain / Q000201:enzymology* / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D006593:Hexokinase / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D008958:Models, Molecular; D014316:Tritium
D014316:Tritium; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006593:Hexokinase; D008274:Magnesium; D005947:Glucose