AP4A-hydrolysing activity in sea urchin embryos

The enzyme activity hydrolysing diadenosine 5,5'-P1, P4-tetraphosphate (AP4A) was demonstrated in the embryonic extract of sea urchin. The enzyme activity was preferentially inhibited by ZnCl2 and by high concentrations of isobutylmethylxanthine, indicating that two types of the enzyme, (AP4A) hydrolase and non-specific phosphodiesterase, are related to the degradation of (AP4A) in sea urchin embryos. The (AP4A)-hydrolysing activity was not detectable in the unfertilized eggs because of the presence of a high-molecular weight (HMW) and thermolabile inhibitory factor. Though the enzymes were activated immediately after fertilization, no cell cycle-dependent fluctuations in their activities were observed.