(ATP:D-hexose 6-phosphotransferase; EC 18.104.22.168)
Hexokinase (HK) catalyzes the phosphorylation of glucose. In
mammals, four distinct enzymes-types I to IV hexokinases-have
been identified. The enzyme is found in most cells, but there
is tissue specificity for the particular type of
hexokinase. Thus skeletal muscle has type II, adipose tissue
has both types I and II, and the liver has all four types of
hexokinases. However, the type IV hexokinase (glucokinase) is
the one that predominates in the liver (Human Biochemistry;
Orten, J.M. and Neuhaus, O.W.; 10th edition, p. 226, 1982,
Mosby, St. Louis).
Two hexokinases, designated P-I and P-II, have been isolated
from yeast. These are separate, noninterconvertible enzymes
(Womack, F.C.; Welch, M.K.; Nielsen, J.; and Colowick, S.P.,
Arch. Biochem. Biophys., 158, 451, 1973). The yeast hexokinase
has a molecular weight of 100,000 and the optimum pH for its
catalytic activity is 7.5.
Hexokinase is used to determine glucose, fructose, mannose and ATP.