Abstract
The temporal relation between hormone uptake, metabolism, and reinitiation of meiosis was investigated following in vitro incubation of immature starfish oocytes with the maturation inducing hormone 1‐methyladenine (1‐MA) and/or ^3^H‐1‐methyladenine (^3^H‐1‐MA).
Oocyte incorporation of the radioactive marker occurred in a dose dependent fashion and in excess of that required for maturation. Uptake and metabolism of the hormone by oocytes took place at subthreshold doses of 1‐MA as well as maturation inducing doses. Oocytes also concentrated radioactivity following incubation with physiologic doses of ^3^H‐1‐MA. Chromatographic analysis of oocyte radioactivity indicated that greater than 90% of the hormone incorporated by the oocytes existed as a single metabolite and this percentage remained constant over a 6‐hour time period. Metabolite was also isolated from the culture media and the quantity in the media increased with increased duration of incubation. After six hours, the metabolite accounted for 28% of the total culture media radioactivity. Determination of the rate of release of ^3^H‐marker from preloaded oocytes indicated that release was insufficient to account for the levels of metabolite found in the culture media. Such results suggest that at least a portion of 1‐MA metabolism occurred to the exterior of the cell membrane. Oocyte uptake as well as release of incorporated radioactivity were both suppressed by incubation at 0°C. However, at 0°C the proportion of oocyte incorporated radioactivity isolated as metabolite was similar to that following incubation at 22°C. The high and constant level of metabolism of incorporated hormone by oocytes, as well as the continued metabolism despite suppression of uptake suggests that a close association exists, possibly at the level of the oocyte cell membrane, between 1‐MA uptake and formation of metabolite in the starfish oocyte.