During experiments on the catalase content of sea-urchin spermatozoa, opportunities arose of measuring the catalatic activity of sea-urchin eggs. Fertilized and unfertilized eggs of Echinus esculentus were examined, the jelly having been removed in each case. Holter & Linderstrom-Lang (1936) and Holter (1937) investigated the catalase content of sea-urchin eggs, but they were particularly concerned with the location of this enzyme in the cell. The catalatic activity of sea-urchin eggs has attracted attention on several occasions in the past (see, for example, Kobert, 1903), but the results were unquantitative and sometimes contradictory. Furthermore, no workers examined the effect of low concentrations of hydroxylamine on the apparent catalatic activity of these cells. Hydroxylamine is a specific inhibitor of catalase as opposed to other substances which catalytically decompose H2O2 into O2 and H2O.
The experimental procedure was the same as that described elsewhere in this Journal (Rothschild, 1950). Twenty-five determinations were made on unfertilized eggs at 15° C. ; the mean catalatic activity, Ac (see immediately preceding paper) was 660. The comparable figure for sea-urchin semen is 90. Unfertilized sea-urchin eggs are notoriously variable in their physiological properties. These experiments were not exceptional in this respect, different batches of eggs showing considerable variability in regard to catalase content. The estimated standard error of the mean was 180. Five comparisons of fertilized and unfertilized eggs were also made, involving twenty-three measurements. The difference between fertilized and unfertilized eggs was insignificant, though in all comparisons the catalatic activity of fertilized eggs was slightly lower than that of unfertilized ones.
Low concentrations of neutralized hydroxylamine hydrochloride almost completely inhibit the catalase activity of the eggs. Fig. 1, which illustrates this, would apply equally well to sea-urchin spermatozoa, both as regards the form of the O2 evolution curve and the inhibition of O2 evolution by hydroxylamine.
Measurements of catalase content cannot be made on eggs in sea water. When an attempt is made to do this, there appears to be a larger evolution of O2 than is theoretically available in the H2O2 added to the egg suspensions. The H2O2 and the high rate of shaking cytolyse the eggs which produce acid. This decomposes the bicarbonate in the sea water, the evolved CO2 causing a positive pressure in the manometer, in addition to that due to O2 evolution.