Studies On the Respiration of Sea-Urchin Spermatozoa

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Abstract
1. The activity of cytochrome oxidase in sea-urchin spermatozoa (Hemicentrotus pulcherrimus) was studied in relation to the Dilution Effect, using dimethyl-p-phenylene- diamine (dpphd), p-phenylenediamine (pphd), hydroquinone, ascorbic acid and cysteine as substrates. 2. All substrates except hydroquinone cause a marked rise in oxygen uptake in dense sperm suspensions (1/20). It is shown that the maximum rate obtained with sufficient amount of dpphd in dense suspensions is almost comparable with the normal respiratory rate in dilute suspensions (1/200). The oxygen uptake of dilute suspensions is not affected by the addition of dpphd. 3. The increase in oxygen uptake caused by dpphd and pphd is completely eliminated by sodium azide (10-2 M). 4. From the results of 2 and 3, it can be inferred that cytochrome oxidase exhibits its maximum activity only in dilute suspension, probably as a result of substrate saturation. 5. Heavy metals, copper and zinc, do not seem to affect the terminal oxidase system directly, but some other part of the oxidation chain, such as the soluble SH groups. 6. The effect of cysteine is rather complicated. In the range from 10-4 to 10-3 M, causes a reduction in the initial respiratory rate as already observed with other amino-acids, but above this range, it exerts a marked stimulatory effect on oxygen uptake.