392 



Courtney, W. A. M., and G. R. W. Denton. 1976. 



Persistence of polychlorinated biphenyls in the hard-clam (Mereenaria 

 mereenaria) and the effect upon the distribution of these pollutants in 

 the estuarine environment. Envir. Pollut. 10: 55-64. 



M. mereenaria from the northern end of Southampton Water contained 0.11 ± 



0.04 parts PCB/IO^ wet body weight. The visceral mass contained 10.0 ± 5.8 



parts/10° after 18 days exposure to 12.5 parts/10 9 A1254. Oysters feed at a 



faster rate and accumulate twice as much DDT as hard clams. The maximum mean 



concentration factor for M. mereenaria exposed to 1.25 parts/10 9 was 1.8 x 

 10-3 for the visceral mass after 18 days. A tenfold increase in exposure 

 level, gave a fivefold increase in tissue concentration so that the biotic 

 concentration factor is dependent upon the level of contamination, and falls 

 as pollution increases. Larger PCB residues in visceral mass compared with 

 muscular foot of M. mereenaria may be related to differences in lipid con- 

 tent of tissues, but the gut and contents were not separated from visceral 

 mass prior to analysis. Contaminated M. mereenaria from Southampton and 

 those exposed to 1.25 parts/10 9 A1254 in the laboratory showed little change 

 in PCB content after 3 months in clean seawater. At a higher dosage there 

 was a significant decrease in PCB residues in the foot after a month although 

 the level in the visceral mass was unchanged after 6 months. Tissues of M. 

 mereenaria contained a predominance of early eluting peaks compared with 

 standard A1254, and feces and surface mud of their habitat also contained a 

 predominance of late eluting peaks, it is possible that they exert a qualita- 

 tive and quantitative effect on distribution of PCB in the system. Densities 

 of 120 clams/m^ have been found in .Southampton Water, and may contribute, 

 through recycling particulate matter on which they feed, to the increased 

 proportion of higher chlorinated PCB isomers in the mud which they inhabit. 

 - J.L.M. 



393 



Coutance, A. 187 8. 



De l'energie et de la structure musculaire chez les mollusques acephales. 

 Paris. 



This is available at Phila. Acad. Nat. Sci. It could not be sent on 

 interlibrary loan because it is in poor condition. Cost of reproduction was 

 25C/page, but we did not have a record of number of pages, and thought the 

 publication would be of peripheral interest for our purposes. Search 

 terminated. - J.L.M. 



394 



Cowgill, Robert W. 1972. 



Susceptibility of paramyosin to proteolysis and the relationship to regions 

 of different stability. Biochemistry 11(24): 4532-4539. 



Paramyosin is one of the major contractile proteins extractable from adductor 

 muscle of mollusks. Contractile units of molluscan muscle have thick and 

 thin filaments. Paramyosin is the major component of thick filaments. 

 Paramyosin molecules align to form a bipolar core of the thick filament which 

 is covered by a surface layer of myosin. The core seems to modify inter- 

 action of myosin with actin of thin filaments, thereby having a specific 

 regulatory role in maintaining muscle tension. Paramyosin molecules are well 

 suited for such a role, for it is a large molecule, of 220,000 atomic mass 

 units, rod-shaped, 1330 A long and 20 A diameter, consisting of 2 intertwined 

 a-helical chains. Paramyosin from Mereenaria mereenaria was attacked rapidly 

 by a variety of proteolytic enzymes. However, a fully helical segment of the 

 molecule soon accumulated, which was resistant to further attack. Essentially 

 the same segment of paramyosin appeared to be resistant to hydrolysis by all 

 enzymes tested. The resistant segment was in the N-terminal two-thirds of the 

 molecule. - J.L.M. 



109 



