82 



TISSUE RESPIRATION IN INVERTEBRATES 



of the subumbrella of the jellyfish (Cassiopea 

 frondosa) and the branchial tree of the sea cu- 

 cumber (Isostichopus badionotus) . Concentrations 

 of cyanide employed by Robbie ranged from 

 1 X 10-2 to 1 X 10-^ M. The fact that even the 

 lower concentrations of cyanide were inhibitory 

 suggests that the cyanide may have been acting 

 on cytochrome oxidase. 



It should be added here parenthetically that 

 cyanide is a less specific inhibitor of cytochrome 

 oxidase than is azide. Furthermore, although 

 both C3^ochrome oxidase and tyrosinase are in- 

 hibited by carbon monoxide, the inhibition of 

 cytochrome oxidase is reversible by light, 

 whereas the inhibition of tyrosinase is not. 



Possibly the inhibition of endogenous respira- 

 tion produced by cyanide in Robbie's study was 

 due to an inhibition of catalase, peroxidase, or 

 tyrosinase. Such a possibility, however, is slight, 

 for the concentration of these enzymes in animal 

 tissues is too low for them to be playing a major 

 role in respiration. The lower concentrations of 

 cyanide that Robbie found to be effective (e.g., 

 1 X 10-5 M) also rule out the possibility that the 

 inhibition depended upon a reaction of this poison 

 with carbonyl groups in keto acids of the citric 

 acid cycle. 



Laser (1944) has found that cyanide can cause 

 an increase in respiratory activity. When he 

 added 0.01 M cyanide to muscle homogenates of 

 Ascaris lumbricoides containing methylene blue, 

 Laser noted an increase in the rate of respira- 

 tion greater than that shown by homogenates con- 

 taining methylene blue but lacking high concen- 

 trations of cyanide. Apparently cyanide can 

 combine with oxaloacetate to form a complex 

 that, unlike oxaloacetate itself, is incapable of 

 competitively inhibiting succinic dehydrogenase. 



Neither cytochrome oxidase nor cytochrome c 

 is enzymatically detectable in muscle homogen- 

 ates of the nematodes Ascaris lumbricoides and 

 Litomosoides carinii, although a low level of 

 cytochrome c and cytochrome oxidase activity is 

 apparent in muscle homogenates of the trematode 

 Schistosoma mansoni (Bueding and Charms, 

 1952). However, a pigment with the same absorp- 

 tion maxima as reduced cytochrome c has been 

 demonstrated spectroscopically in tissues of 

 Parascaris equorum and A. lumbricoides 

 (Keilin, 1925) and in those of A. lumbricoides at 

 the temperature of liquid air (Keilin and Hartree, 

 1949). Thus the conclusion that these parasitic 



nematodes have a unique terminal electron trans- 

 port system (Bueding and Charms, 1952) re- 

 mains open to question. 



Because the respiration of the diapausing 

 Cecropia moth is unaffected by cyanide and 

 carbon monoxide, Schneiderman and Williams 

 (1954a, 1954b) postulated that a terminal oxidase 

 other than cytochrome oxidase functions during 

 pupal diapause. Subsequently, by use of low tem- 

 perature spectroscopy (see Keilin and Hartree, 

 1949), which intensifies the absorption bands of 

 the cytochromes 10- to 20-fold, Shappirio and 

 Williams (1957a) observed that cytochrome oxi- 

 dase is still present in diapausing Cecropia 

 pupae. During their study, in which they care- 

 fully traced the activity of the enzymes of the 

 terminal electron transport system in wing 

 epithelium during a portion of the life cycle, 

 Shappirio and Williams (1957b) found that the 

 activity of cytochrome oxidase falls to low (but 

 still detectable) levels during diapause and then 

 rises during adult development. They also found 

 (1957a) that the concentration of this and other 

 respiratory enzymes drops markedly during 

 pupal diapause and then rises again during adult 

 development. Significantly, however, whereas 

 during diapause the concentration of cytochrome 

 c is less than 5 per cent of its pre-diapause level, 

 that of cytochrome oxidase remains relatively 

 high (20% of its non-diapause level). 



Recently Harvey and Williams (1958a, 1958b) 

 and Kurland and Schneiderman (1959) reinvesti- 

 gated the question of the terminal oxidase in 

 diapausing pupae. Respiration of the whole ani- 

 mal throughout diapause is relatively insensitive 

 to inhibition by carbon monoxide, azide, and 

 cyanide. Nonetheless, Harvey (1956), Kurland 

 and Schneiderman (1959), and Harvey and Williams 

 (1961) showed that injury-stimulated and dini- 

 trophenol-stimulated uptake of oxygen by dia- 

 pausing pupae is indeed sensitive to carbon 

 monoxide. Furthermore, in their independent 

 investigations, Kurland and Schneiderman (1959), 

 studying total uptake of oxygen, and Harvey and 

 Williams (1958b), studying the heart beat of un- 

 injured diapausing pupae, demonstrated that at 

 low oxygen tensions the diapausing pupa is carbon 

 monoxide sensitive. The manometric studies 

 were measurements of the total gas uptake in the 

 presence of either oxygen or oxygen and carbon 

 monoxide mixtures. That diapausing pupae may 

 consume carbon monoxide as well as oxygen has 



