M. Bedin et al., Platelet Na+,K+-ATPase activity as a possible peripheral marker for the neurotoxic effects of phenylalanine in phenylketonuria, METAB BRAIN, 15(2), 2000, pp. 115-121
The in vitro effects of phenylalanine or alanine alone or combined on Na+,K
+-ATPase activity in membranes from human platelets were investigated. The
enzyme activity was assayed in membranes prepared from platelet-rich plasma
of healthy donors. Phenylalanine or alanine were added to the assay to fin
al concentrations of 0.3 to 1.2 mM, similar to those found in plasma of phe
nylketonuric patients.
Phenylalanine inhibited Na+,K+-ATPase activity by 20-50% [F(4,25)=11.47;p<0
.001]. Alanine had no effect on Na+,K+-ATPase activity but when combined wi
th phenylalanine prevented the enzyme inhibition. These results, allied to
others previously reported on brain Na+,K+-ATPase activity, may reflect a g
eneral inhibitory effect of phenylalanine on this important enzyme activity
. Therefore, it is possible that measurement of Na+,K+-ATPase activity in p
latelets from PKU patients may be a useful peripheral marker for the neurot
oxic effects of phenylalanine.