l. REACTION PRINCIPLEs
Creatine kinase
(ATP:creatine N-phosphotransferase,
EC
2.7.3.2, CK)
catalyzes the dephosphorylation of creatine
2+
phosphate by Mg
-ADP cornplexes.
The rnethod cornprises three coupled enzyme reactions (15,16):
Creatine kinase
Creatine phosphate
+
ADP
~------
Creatine
+
ATP
(I)
EC 2.7.3.2
Hexokinase
ATP
+
D-Glucose _______ ADP
+
D-Glucose-6-phosphate
'
-
(II)
EC 2.7.1.1
Glucose-6-phosphate-dehydrogenase
+
"
Glucose-6-phosphate
+
NADP
D-Glucono- -lactone-6-
+
phosphate
+
NADPH
+
H
EC 1.1.1.49
(III)
The equilibriurn of I favours the formation of creatine and
ATP at pH values around 6- 7 (l4).The true substrates are
2+
the Mg
-ADP complex and free creatine phosphate (CP). For
the sake of practicability concentrations are given below as
total ADP, Mg, and creatine phosphate.
The prirnary reaction (I ) is coupled t h rough the auxiliary
hexokinase reaction (II) to the NADPH-forrning indicator reac–
tian (III) catalyzed by glucose-6-pho sphate dehydrogenase.
For increased precisi on at : ow cataly tic acti v ity c oncentra–
tions an add iti o nal re ac ti o n I V h as bee n propo sed c ompris i ng
6-phosphoglucono lactonase ( EC 3.1.1.31 ) a n d 6-pho s phogl u c o –
nate dehydrogenase ( EC 1.1.1. 43) ( 17) .
18
Klinisk kemi
i
Norden 2: suppl, 1990
