DOES THE RESPIRATORY RATE IN SEA-URCHIN EMBRYOS INCREASE DURING EARLYDEVELOPMENT WITHOUT PROLIFERATION OF MITOCHONDRIA

During early development of the sea urchin, the respiratory rate, enha nced upon fertilization, is maintained up to hatching (pre-hatching pe riod) and then gradually increases to a maximum at the gastrula stage (post-gastrula period). Except for a short duration after fertilizatio n, respiration in embryos is strongly inhibited by CN- and antimycin A . During the whole span of early development, the amounts of proteins, cytochromes and the specific activities of cytochrome c oxidase and r educed nicotinamide adenine dinucleotide (NADH) cytochrome c reductase in mitochondria are practically the same as in unfertilized eggs. A m arked augmentation of mitochondrial respiration after hatching probabl y occurs without net increase in whole mitochondrial intrinsic capacit ies. Carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) or tetra methyl p-phenylenediamine (TMPD) enhances the respiratory rate in the pre-hatching period but hardly augments the respiration in the post-ga strula period. In the presence of both FCCP and TMPD, the respiratory rate in the pre-hatching period was as high as in the post-gastrula pe riod. Probably, electron transport in the mitochondrial respiratory ch ain is regulated by acceptor control and limitation of cytochrome c re duction in the pie-hatching period and released from those regulations in the post-gastrula period. Acceptor control of respiration is exper imentally reproduced in isolated mitochondria by making adenine nucleo tide revels as those levels in the pre-hatching period.