On the oxidation processes of the echinoderm egg during fertilisation

Abstract

The following paper is concerned with an investigation of the oxidation processes of the animal egg-cell during fertilisation. The subject has already received considerable attention and the problem has been approached from many different aspects. The first to attempt to measure in definitive quantitative manner the oxygen consumption of the egg on fertilisation, was Warburg(1) in 1908. He made use of the sea-urchin Arbacia , and estimated the amount of oxygen that had disappeared from the sea-water in which the eggs had remained for some time. The Winkler titration method was employed. He found that a quantity of eggs that gave a Kjeldahl determination of 28 mgrm. of egg nitrogen, which corresponds roughly to about 4 million eggs, 4—5 c. c. of oxygen was taken up in the first hour following fertilisation, while the same quantity of unfertilised eggs only consumed 0·5-0·7 c. mm. of oxygen in this time. The fertilised egg, therefore, took up six to seven times more oxygen than the unfertilised egg. Loeb had previously predicted, that the main function of the sperm in the process of fertilisation was that of setting up a series of oxidations on its entrance into the cytoplasm of the egg. Warburg’s work was a remarkable confirmation, therefore, of Loeb’s prediction. This first paper was followed up by a long series of papers which have added greatly to our knowledge of the oxidation processes taking place in the egg on fertilisation. In addition, our knowledge has also been greatly extended by the numerous papers of Loeb, and especially the papers of Loeb and Wasteneys (2) in which quantitative measurements were also carried out. In 1911 appeared the large paper of Meyerhof (3) in which the heat liberation was measured and correlated with the oxygen consumption. In all these papers the Winkler method was employed; there are, however, many drawbacks to the use of this method, and in the recent work of Warburg and Meyerhof it has been finally abandoned for the more convenient and accurate manometer. The great advantage of the manometer method lies in the fact that it can be used equally well for both oxygen and carbon dioxide determinations, and that continuous observations can be carried out minute by minute on the respiratory exchange of the material under investigation. Warburg (4) (1915), using this instrument, has recently reinvestigated the respiratory exchange in the egg of the sea-urchin Strongylocentvotus during the first 24 hours of development. He found that a quantity of unfertilised eggs that contained 20 mgrm. of egg nitrogen, which corresponds to about 3 million eggs, consumed in 20 minutes 10-14 c. mm. of oxygen at a temperature 23° C. and barometer 760 mm. Hg. The fertilised egg under the same conditions, 10 minutes after the addition of the sperm, consumed 60-84 c.mm. That is 10 minutes after fertilisation the oxygen consumption of the egg was six times that of the unfertilised egg, and that there was already a rise of 500 per cent, in the oxidation rate of the egg in this time. In the sixth hour the oxygen consumption was twelve times that of the unfertilised egg, at 12 hours it was sixteen times, while at 24 hours it was twenty-two times the amount of the unfertilised egg. As Warburg remarks, it is extraordinary that in one and the same cell substance, which receives no addition of fresh material from any external source, we should find, as the result of fertilisation in the course of 24 hours, a rise in its oxidation rate of something like 2000 per cent. On the whole the manometer method seemed to show that there was a much closer agreement between the increase in the respiratory quotient and the appearance of visible structure in the egg, than had been demonstrated in previous work where the Winkler titration method had been employed. In all instances the CO 2 output of the eggs followed closely the oxygen uptake, the respiratory quotient being in the neighbourhood of 0·9. The respiration of a single spermatozoon was found to be about 1500-2000 times less than that of the egg. In the past season, working at Naples, I have been able to carry the investigation of the problem a step farther, by the use of a special type of the Barcroft differential manometer, in which it was possible to bring about the fertilisation of the eggs in the closed chamber of the apparatus, and so for the first time the measurement of the respiratory exchange during the period the sperm were actually making their way into the egg was rendered possible. The eggs and sperm of Echinus microtuberculatus were used.