Polymorphism in fowl serum albumin. VI. Changes in in vitro protein synthesizing activity in developing embryonic fowl liver

Summary Cell-free protein synthesizing systems were prepared from the livers of chick embryos at selected ages and the characteristics of individual fractions were compared. While polysomes showed decreasing size with older embryos, isolated polysomes did not differ significantly in amino acid incorporating activity when assayed with standard cell sap. When assayed with standard polysomes, cell sap activity decreased with increasing developmental age whether incorporation was measured using [³H]lysine, [³H]leucine, or [³H]aminoacyl-tRNA. Free amino acid concentrations in the cell sap showed reproducible independent variation during development which was taken into consideration in calculating net amino acid incorporation. A large increase in ribonuclease activity was observed during development; however, nuclease inhibitor activity was absent before day 15 but increased thereafter. Aminoacyl-tRNA synthetase activity did not vary significantly. It is proposed that the observed changes in the rate of cell-free protein synthesis result not only from increasing ribonuclease activity with increasing developmental age but also from changes in the activity of other soluble factors.This is paper VI in a series; paper V is reference 6. The series title is based on earlier work with systems derived from fowl which synthesized two genetic variants of serum albumin²¹.This research was supported in part by a grant from the Damon Runyon Memorial Fund (DRG-1125). Dr. H. M. Jernigan was an N.I.H. Postdoctoral Fellow (5 F02 GM 50944-02).To whom all inquiries are to be addressed.     

Conformational analysis of receptor selective tachykinin analogs: senktide and septide.

The conformational behavior in solution of two receptor selective tachykinin agonists, senktide (succinyl-D-F-MeF-G-L-M-NH2) and septide (pQ-F-F-P-L-M-NH2) is described. Two dimensional cross relaxation NMR spectroscopy is used together with coupling constant data to obtain interproton distance constraints. These results are used in conjunction with semi-empirical energy computations to indicate favorable conformations. Senktide is found to have a high degree of conformational order which is attributed to rotational restriction associated with the N-methylation of phenylalanine. The lowest energy conformation in accord with the experimental interproton distances contains a beta-turn. Interproton distances indicate that septide exists as a random coil or in an extended chain conformation. Energy computations suggest that septide is primarily an extended chain with internal reorientation restricted by the proline residue. These results may be related to the selectivity of these peptides for different receptors, in that the analogs, with conformations more stable than tachykinins, are more receptor selective.