Activation of apo-ALAT
with pyridoxal-5'-phosphate
The IFCC, ASAT and ALAT Reference Methods include activation
of the apo-enzymes by pyridoxal-5'-phosphate, (P-5'-P, 1,2).
After careful consideration of the advantages and disadvanta–
ges of this procedure the ECCLS Subcommittee decided to in–
clude this step.
Addition of Pyridoxal-5'-phosphate to serum activates the
apo-enzymes and permits the measurement of total ASAT and
ALAT catalytic activity concentrations in serum. Provided the
saturation with P-5'-p is complete, this eliminates between–
sample variations in the proportion of apo-enzyme. The avera–
ge increases relative to measurements of ASAT and ALAT with–
out activation are in the range 1.3 - 1.5 and 1.2 - 1.4, re–
spectively (l- lO a,b).
However, measurement of .P-5'-P activated ASAT and ALAT chang–
es reference ranges previously established in the absence of
P-5'-P, since some apo-enzyme is almost always present in
healthy individuals. As ASAT and ALAT are activated to diffe–
rent degrees, clinically useful ratios between the ASAT,
ALAT,
and other enzymes are also changed. In the majority of
cases clinical information is not significantly increased
through the use of P-5'-P compared with that obtained by me–
thods in which this coenzyme is not added. This applies also
to patients suffering from the relative deficiencies in B-vi–
tamins that may be encountered in Europe. However, the normal
or abnormally low levels of ALAT observed in some severely
ill patients in the absence of added P-5'-p may be converted
to abnormally raised val u es ln assay s with t h e added coenzyme
(4, 8, 9). Saturat i on of apo-ASAT and apo-ALAT in human sera
may be obtained in three ways, and different procedu res have
been ehosen in vari o us National re comrnendations (7- 16).
56
Klinisk kem i
i
Norden 2: supp/, 1990
