31P-NMR analysis of sea urchin sperm activation. Reversible formation of high energy phosphate compounds by changes in intracellular pH.

31P-NMR has been used to estimate the internal pH (pHi) of sperm from the sea urchin Strongylocentrotus purpuratus. The values for pHi obtained from the chemical shift of inorganic phosphate agree well with those obtained from amine accumulation. At low pHi, when sperm are quiescent (immotile and non-respiring), they accumulate phosphocreatine (PCr), but have a low level of inorganic phosphate (Pi). Conversely, when the pHi is elevated, sperm respiration and motility are activated, PCr is decreased and Pi is increased. This change is reversible upon decrease of the pHi, whereupon respiration and motility are arrested, Pi disappears and PCr increases. We conclude that the overall balance of energy metabolism, and thus the phosphate potential, of sea urchin sperm are under the control of the pHi.