K+-p-nitrophenylphosphatase (K+pNPPase) is the enzyme, which
is considered to be involved in K+-dependent hydrolysis of the
phosphoenzyme in the reaction cycle of Na+, K+-ATPase. The aim
of our present study was to characterize some features of
K+pNPPase in homogenates of the rat brain and liver. We
determined p-nitrophenylphosphatase (pNPPase) activity in the
presence of various ion combinations (Mg2++K+, Mg2+, K+). We
found a higher total pNPPase activity in the brain (0.8±0.079
nkat/mg protein) than in the liver (0.08±0.01 nkat/mg protein).
Contrary to the liver, the main part of the total brain activity was
K+-dependent. The activity of K+pNPPase was significantly higher
in cerebral cortex homogenates (0.86±0.073 nkat/mg protein) in
comparison to those of the whole brain (0.57±0.075 nkat/mg
protein). The specific K+pNPPase activity was two times higher in
the isolated pellet fraction (0.911±0.07 nkat/mg protein), rich in
synaptosomes, compared to the whole brain homogenate
(0.57±0.075 nkat/mg protein). Our results demonstrate the high
activity of K+pNPPase in the brain tissue and its distribution
mainly into the pellet fraction, what might indicate a possible role
of K+pNPPase in specific structures of the brain, e.g. in
synaptosomes.
K+-p-nitrophenylphosphatase activity in rat brain and liver
