Physiological Response of the Cunner, Tautogolabrus adspersus, 
to Cadmium. 
V. Observations on the Biochemistry 
EDITH GOULD and JOHN J. KAROLUS' 
ABSTRACT 
In the liver of cunner, Tautogolabrus adspersus, exposed to 3 ppm and to 24 ppm Cd for 96 
hr, aspartate aminotransferase activity was 71% and 59%, respectively, of the activity in livers 
of control fish. 
In the livers of cunners exposed to 24 ppm Cd, nicotinamide-adenine dinucleotide reductase 
activity required 20 mM Mg for activation of the same order that 2 mM Mg produced in control 
livers. 
Although individual variation precludes generalization here, what may be a metal- 
complexing group of proteins in the serum of cadmium-exposed cunner warrants further elec- 
trophoretic study. 
INTRODUCTION 
In the collective effort to determine the effects of 
heavy metals on the marine ecology, relatively little 
attention has been directed toward possible 
biochemical malfunctions in marine animal tissue. 
Yet apart from acute physical trauma, such as gross 
occlusion of gill tissue, the earliest response of a 
marine animal to physiological challenge by sublethal 
concentrations of heavy metals is at the molecular 
level. 
Normal metabolic response to the ingestion or ab- 
sorption of heavy metals is their temporary inactiva- 
tion by serum proteins, which sequester and transport 
the metals to the liver for further processing for 
removal from the body. Furst, Flessel, and Kelly 
(1972) observed that noncancer-causing metals, such 
as zinc and iron, are carried by a- and _ 6-globulins, 
whereas those heavy metals definitely known to be 
able to cause cancer, such as nickel and cadmium, are 
carried by albumins, the major metal-transport pro- 
tein of blood. Serum electrophoretic patterns may 
conceivably be a means of detecting an abnormal 
proportion of metal-protein complexes. 
If the normal biochemical mechanisms are unable 
wholly to inactivate the heavy metals, toxic effects 
follow. The ionic character of the blood serum 
becomes seriously deranged (Lewis and Lewis, 1971), 
with consequent osmoregulatory distress (Thurberg 
and Dawson, this report, Part III). Key ligand af- 
finities of some enzymes, particularly those for which 
divalent cations act as positive or negative effectors, 
can be distorted by a changing ionic environment, 
‘Milford Laboratory, Middle Atlantic Coastal Fisheries Center, 
National Marine Fisheries Service, NOAA, Milford, CT 06460. 
21 
with consequent changes in their capacity to react 
(Gould, 1969, 1971). 
Such effects on biochemical systems are most readi- 
ly assayed by measuring changes in the activity of 
their constituent enzymes. Because it is not always 
clear what systems are involved, one must look either 
to enzymes that are known to sequester metals or to 
those that require metals for their proper catalytic 
functioning. Jackim, Hamlin, and Sonis (1970), for 
example, in their acute-static study of heavy-metal 
poisoning in the liver of mummichog, Fundulus 
heteroclitus, selected three metal-requiring enzymes 
(alkaline phosphatase, xanthine oxidase, and 
catalase), the metal-sensitive ribonuclease, and acid 
phosphatase, an enzyme involved in mineral 
metabolism. 
In the multidisciplinary study reported here, the 
cunner, Tautogolabrus adspersus, was exposed for 96 
hr to varying concentrations of cadmium, a soft Lewis 
acid with the capacity to bind strongly and irrevers- 
ibly to sulfur groups. It may be well to note here that 
the nature of cadmium-protein bonding has been 
observed to differ with the duration of actual metal 
challenge (Nordberg, Piscator, and Lind, 1971): in 
mouse liver shortly after a single injection of cad- 
mium, the cadmium-protein complex was of high 
molecular weight, whereas in livers of mice surviving 
for more than 24 hr after injection, the cadmium was 
bound to a protein of low molecular weight—probably 
the sulfur protein metallothionein, whose synthesis by 
the liver is stimulated by prolonged exposure to cad- 
mium (Anonymous, 1972). More importantly, in vitro 
binding of cadmium by liver homogenates—which 
would be rapid—is nonselective, and will inhibit 
sulfhydryl-dependent enzymes, whereas a 
metallothionein-cadmium complex has no such in- 
