395 



Cowgill, Robert W. 1974. 



Location and properties of sulfhydryl groups on the muscle protein paramyosin 

 from Meraenavia mercenavia. Biochemistry 13(12): 2467-2474. 



Earlier studies showed that paramyosin was susceptible to proteolysis in such 

 a way that a common segment or proteolytic-resistant core remained after 

 attack by any one of a number of enzymes. Those studies were made with 

 paramyosin which had all sulphhydryl groups oxidized to disulphide form. 

 These results were not affected by state of oxidation of paramyosin, for the 

 same paramyosin pepsin-resistant core (PPC-1) and paramyosin trypsin- 

 resistant core (PTC-1) were obtained by proteolysis of paramyosin whether 

 sulphhydryl groups were oxidized or reduced. But some physical properties 

 of paramyosin do depend on state of oxidation of its sulphhydryl groups. 

 Experiments reported in this paper showed that the N pair disulphide bond 

 contributes to the high stability of the N-terminal segment of the 

 paramyosin molecule. The C pair disulphide bond does not appear to 

 stabilize the C-terminal region of the molecule. - J.L.M. 



396 



Cowgill, Robert W. 1975. 



Segments of paramyosin formed by cleavage at sites of cysteine residues. 

 Biochemistry 14(19): 4277-4279. 



Helical muscle protein 3-paramyosin of 200,000 daltons was treated for 

 chemical cleavage of the polypeptide chain at the site of Cys residues. 

 The protein cleaved into 2 segments: CCF-1 of 140,000 daltons, and CCF-2 

 of 60,000 daltons. CCF-1 was completely helical and CCF-2 was 85% 

 a-helical. Molecular size, resistance to pepsin digestion, stability to 

 heat and urea, and solubility of CCF-1 were similar to those of a pepsin- 

 resistant segment PPC-1 described by the author in 1972. It was concluded 

 that the CCF-1 segment arose from the N-terminal 2/3 of the paramyosin 

 molecule. The properties of CCF-2 were distinctly different. It arose 

 from the C-terminal 1/3, and had limited solubility at neutral pH which 

 matched the low solubility of paramyosin. It was concluded that the CCF-2 

 region is responsible for the self-aggregating tendency of paramyosin at 

 neutral pH and low ionic strength. - modified author's abstract - J.L.M. 



397 



Cowgill, Robert W. 1975. 



Proteolysis of paramyosin from Meraenaria meraenaria and properties of its 

 most stable segment. Biochemistry 14(3): 503-509. 



The helical muscle protein paramyosin appears to consist of 3 segments of 

 about equal size that differ in stability to guanidine hydrochloride and 

 heat. The N-terminal segment is most stable, the C-terminal segment least. 

 These differences were used to design proteolytic digestions to remove 

 segments of low and intermediate stability specifically. At room temp 

 only the C-terminal region was digested by pepsin or trypsin. Proteolytic 

 removal of the C-terminal region caused the remaining 2/3 of the paramyosin 

 molecule to accumulate as a segment (PPC-1) of 140,000 daltons still in 

 stable helical conformation. Under more rigorous conditions, e.g., papain 

 digestion of either paramyosin or PPC-1 in 4M guanidine - HC1 , which might be 

 expected to destabilize all but the N-terminal segment, all except the 

 region that was cleaved. The N-terminal region accumulated as a helical 

 segment of 74,000 daltons (PPC-2) if digestion was limited to 1.5 hr, or a 

 segment of 58,000 daltons (PPC-3) if digestion continued for 24 hr. 

 Stability of the 3 PPC segments to guanidine -HC1 and heat was measured by 

 change in fluorescence of tyrosyl residues upon loss of the helical form. 

 Stability of segments corresponded well with stability of those regions in 

 the paramyosin molecule from which the segments were thought to come. 

 Amino acid composition of PPC segments and of paramyosin were all very 

 similar. Prediction of relative stability of these helical proteins by 

 inspection of gross amino acid composition does not appear promising. 

 - modified author's abstract. - J.L.M. 



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