Abstract
Dejellied __Rana pipiens__eggs were crushed by centrifugation and clear extracts were prepared by further centrifugation at 150,000 Γ G for 2 h. The extracts were kept at 0Β°C for 2 to 3 weeks. At intervals during the storage period, 80βnl aliquots were injected into ovarian oocytes to assay maturation promoting factor (MPF). In most cases, MPF activity disappeared from the extracts on day 3 or 4, but reappeared on the following days and persisted 2 or 3 days at high levels before disappearing again. The cycle of MPF activity in extracts was repeated fairly regularly a few times during storage of the extracts. The average period of the oscillation was 5.05 + 1.25 days. If a single extract was assayed by oocytes from different frogs, all the assays exhibited exactly the same patterns of changes in MPF activity during storage of the extract. This indicates that the oscillations in MPF activity observed during storage of the extracts reflect changes in MPF activity intrinsic to the extracts, rather than fluctuations in the sensitivity of recipient oocytes to MPF. The reappearance of MPF activity in stored extracts was sensitive to Ca and dependent on Mg ions. The MPF activity that recurred periodically in coldβstored extracts was indistinguishable from that contained in fresh extracts, since oocytes induced to mature by the recurring MPF activity had chromosomes condensed to meiotic metaphase and were capable of cleavage when injected with a sperm suspension. The oscillatory behavior of MPF activity observed in this study may be comprehended on a conceptual basis by aid of a kinetic model.