N Ss
0 o o «i fF
tl I I N N
HO—F—O—P—O-F —0 O
OH OH OH
H
OH OH
Adenosine triphosphateFor the Na/K pump, one molecule of ATP will power one cycle of
the pump, in which three Na ions are pumped out of the cell and
two K ions are pumped in. Consider this: a human body at rest needs
approximately one kilocalorie per minute to maintain life (what is
called a calorie in nutrition is actually the energy unit of a kilocalorie
in physics). This is called the basal metabolic rate of energy consump-
tion. It varies by body size (larger bodies use more energy) and by age
(older people generally use less energy), but one kilocalorie per minute
is a good rough approximation. That works out to be about 1440
kilocalories per day. If one moves around, then several hundred more
kilocalories are required to power the action of muscles. Within the
body, the brain accounts for a large amount of energy consumption,
perhaps 25 percent of the total basal consumption, or about 360 kilo-
calories per day. Of the energy usage by the brain, about 60 percent
of it—amounting to about 220 kilocalories per day—goes to run the
Na/K pumps. That’s quite a lot of energy just to power a single type of
protein in the brain. Clearly, Na/K pumps must be doing something
pretty important.