Energy transport and cell polarity: relationship of phosphagen kinase activity to sperm function

The energy required for motility of sea urchin sperm is transported from the mitochondrion to the flagellum by a phosphocreatine shuttle involving diffusion of phosphocreatine (PCr) between isozymes of creatine kinase (CrK) localized at the two sites (Tombes and Shapiro, Cell, 41:325, '85; Tombes et al., Biophys. J., 52:75, '87). The present studies demonstrate that high sperm CrK (various echinoderms; sea squirt, bristle worm, salmon) or arginine kinase (molusc, barnacle, moth) activity is seen in several species with sperm of a primitive morphology (mitochondrion at the base of the head, relatively long flagellum). In contrast, CrK activity is 10-100-fold less abundant in sperm of other species (frog, mouse, rooster, rabbit, bull, and human) that either possess a modified morphology (mitochondria that extend along the flagellum) and/or utilize glycolytic metabolism. We interpret these findings as support for the use of phosphagen kinase-dependent energy transport in cells in which the production of adenosine triphosphate (ATP) by the mitochondrion is distant from its utilization, leading to a form of metabolic polarization. Two other cell types, frog photoreceptors and rabbit oviduct cells, whose morphology and function also suggest that they exhibit metabolic polarization, contain relatively high CrK activity. The presence of high phosphagen kinase activity in metabolically polarized gametes and somatic cells further substantiates the role of such enzymes in facilitating energy transport.