A biochemical pathway for a cellular behaviour: pH i , phosphorylcreatine shuttles, and sperm motility

Sperm motility and respiration are tightly coupled processes, both activated by an increased intracellular pH (pH i ). As the sperm pH i increases, the flagellar motor driving motility is activated, leading to ATP consumption. Energy for motility is provided by mitochondrial respiration; energy transport from sperm mitochondrion to tail involves distinct isozymes of creatine kinase that effect a phosphorylcreatine shuttle. The activation of sperm motility and respiration can be described as a linked series of biochemical reactions that form a cell behavioural pathway analogous to the reaction sequences of intermediary metabolism.