Adenosine triphosphatase in the embryonic development of the loach

The ATPase (ATP-phosphohydrolase) activity of homogenates of eggs of the loach Misgurnus fossilis L. was investigated at various stages of development. Mg-2+- and Ca2- minus 2+-stimulated ATPases are the predominant forms of ATPase activity in the egg, and their level is almost constant during development. The loach egg also contains (Na-+--K-+)-dependent ATPase, which is maximally active at pH 6.85 and at a ratio Na-+:K-+ Equals 5:1. This activity is negligible or absent in homogenates of unfertilized eggs, increases during cleavage, but disappears at the end of the period of cleavage. After this, the (Na-+--K-+)-ATPase activity increases all the way up to the end of the period studied (the gastrula stage)mthe results are discussed in connection with the literature data on changes in ionic homeostasis and other characteristics during early embryogenesis.