FISHERY BULLETIN; VOL. 70, NO. 3 



OoOO°° 



o 



o 



" %®'o °o 



ELECTROPHORESIS 



(-) 



Figure 6. — Peptide map of a tryptic digest of component 

 S. Chromatography was done with n-butanol-acetic- 

 acid-water (4:1:5) ; electrophoresis was at pH 3.6 in a 

 pyridine-acetic acid-water buffer (1:10:289). The pep- 

 tide map of component F was identical except that pep- 

 tides designated S were not seen and the peptide F was 

 present. 



DISCUSSION 



From the immunodiffusion data we know that 

 the S and F proteins are related to mammalian 

 growth hormone. Their molecular weights also 

 were near the values found for mammalian 

 growth hormone and prolactin. One other ob- 

 servation which will be reported in detail later 

 (Seavey et al., 1972)" was that the amino acid 

 compositions of the tryptic peptides of the pep- 

 tide maps closely resembled those of bovine 

 growth hormone (Seavey et al., 1971). But be- 

 cause there were six half-cystine residues in both 

 S and F and because each contained two residues 

 of tryptophan, these two shark proteins are more 

 like mammalian prolactins than the growth hor- 

 mones which have only four half-cystines and 

 one residue of tryptophan. Therefore, the pro- 

 teins are not only very similar to each other, but 

 are immunologically related to growth hormone 

 and have structural resemblances to both growth 

 hormone and prolactin. These results support 

 the view that growth hormone and prolactin 

 may have developed from a common ancestral 



* Seavey, B. K., R. N. P. Sigh, U. J. Lewis, and R. 

 Lasker. 1972. Tentative structure for a growth hor- 

 mone-like, prolactin-like protein of the shark. 



protein. In the blue shark they appear as sep- 

 arate but yet quite similar substances with simi- 

 larities to both growth hormone and prolactin. 

 It will be interesting to see if there are two such 

 proteins in the pituitary gland of cyclostomes. 

 If not already clear we would like to stress 

 the point that no biological activities have been 

 determined for the S and F components. Our 

 assignment of growth hormone-like and prolac- 

 tin-like properties are based on immunological 

 and structural data alone. How these two com- 

 ponents are related to the biological activities 

 that have been reported for the shark pituitary 

 gland is not known. Extensive biological studies 

 are now needed to characterize these proteins. 

 Also, more study will be given to the altered 

 forms of the substances, and in particular the 

 modification that was produced by incubation 

 at 37°C. This type of study will be given to 

 the altered forms of the hormones because of 

 the rapid alterations that occurred even in the 

 intact pituitary of the shark. We have observed 

 that the prolactin activity of human growth 

 hormone is increased when a hexapeptide is re- 

 moved from the hormone by an enzyme present 

 in pituitary extracts (Lewis et al, 1971). Bio- 

 logical activity of the shark hormones may also 

 be aflFected by such changes. The nature of the 

 alteration that occurs in the shark proteins is 

 not known, but from our experiences with mam- 

 malian hormones we suspect that it is a result 

 of deamidation, enzymic action, or a combina- 

 tion of both. The ease with which the shark's 

 S and F components are converted to more acidic 

 forms, however, strongly suggests deamidation, 

 and the unusually large number of glutamic acid 

 residues may actually be glutamines which rap- 

 idly lose ammonia. 



ACKNOWLEDGMENTS 



Much of this work was made possible by a 

 grant from the National Institutes of Health 

 (AM-09537). We also gratefully acknowledge 

 the support given the project by the National 

 Science Foundation in making the facilities of 

 the RV Alpha Helix available for a 5-day cruise 

 to study the pituitary of the blue shark. We 

 are indebted to Dr. Y. N. Sinha of the Division 



938 



