STUDIES ON THE MECHANISM OF ACTION OF IONIZING RADIATIONS. IV. EFFECT OF X-RAY IRRADIATION ON THE RESPIRATION OF SEA URCHIN SPERM

¹ Argonne National Laboratory, Chicago; the Chemical Division, Department of Medicine, The University of Chicago, Chicago; and The Marine Biological Laboratory, Woods Hole, Massachusetts

The respiration of sea urchin (Arbacia punctulata) sperm increased with dilution up to a dilution of 1:200, where maximum values were found. At this dilution the average Qo₂ value was 19.6 ± 3.9. When the dilution was increased to 1:1000 the respiration dropped sharply to 2.0. A dilution of 1:1600 gave no measurable respiration.

The respiration of dilute suspensions of sea urchin sperm (1:200) was inhibited by x-ray irradiation. A dose of 20,000 r produced an inhibition of 66 per cent which was further increased during the second hour; 10,000 r inhibited 30 per cent; 1000 r, 22 per cent; 500 r, 14 per cent; and 100 r, 10 per cent. When sperm was irradiated with 1000 r there was no recovery of respiration five hours after irradiation. Inhibition of respiration cannot be attributed to hypothetical H₂O₂ formation, for sperm suspensions contain catalase. The catalase value of sperm is 33 c.mm. O₂ formed by 1 mg. dry weight per hour, i.e., 3 micromoles H₂O₂ destroyed. On addition of succinate and of acetate to sperm irradiated by x-rays the O₂ uptake inhibition increased.