A study of the metabolism of Bermuda marine invertebrates at 25°C. shows that the respiratory rates of many of the tissues approximate those of vertebrate tissues at the same temperature. There is no apparent correlation between respiratory rate and phylogenetic development: tissues from some of the simpler forms use as much oxygen per unit weight as those from certain of the more highly developed animals.

Cyanide inhibition experiments reveal a great variation in the amount of oxygen consumption which is dependent upon sensitive heavy metal systems. Three types of tissues, the jellyfish Cassiopea frondosa, the branchial tree of the sea cucumber, Stichopus möbii, and two kinds of tunicates, were completely unaffected by even 10–2M HCN. Other tissues such as sea urchin sperm, squid gills, and lobster nerve and muscle were almost completely inhibited by much lower concentrations. Most of the materials retained 20 to 40 per cent of the normal respiratory rate in 10–2M HCN. The possibility that vanadium may play a part in the oxidation-reduction systems of the completely resistant animals is discussed.

There is a thousandfold variation in the concentration of cyanide required to produce 50 per cent inhibition of respiration in the different tissues. Sea urchin sperm is 50 per cent inhibited by 10–6M HCN: the sea fan requires 10–3M for the same effect. Other tissues lie at intermediate points.

When the logarithm of the ratio of the inhibited to the uninhibited respiration is plotted against the concentration of cyanide the resulting line has a slope which in most cases approximates 1. This indicates that one mole of enzyme ordinarily combines with one mole of inhibitor.

Eggs of the sea urchin, Tripneustes esculentus, show a three- to fivefold increase in the rate of oxygen uptake on fertilization. The respiration of both the fertilized and unfertilized eggs is almost entirely inhibited by 10–4M HCN. Cell division in the fertilized eggs is blocked by somewhat less than 10–5M cyanide, a concentration which reduces respiration to 40 per cent of the normal level.

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