Specific ion concentration as a factor in barotolerant protein synthesis in bacteria

Hydrostatic pressure studies of native and synthetic thick filaments: II. Native thick filaments from rabbit skeletal muscle

Native thick filaments isolated from freshly prepared rabbit psoas muscle were found to be resistant to pressure-induced dissociation. With increasing pressure application and release, a bimodal distribution of filament lengths was observed. The shorter filament length is associated with filament breakage at the center of the bare zone, while the longer length is associated with relatively intact filaments. Intact filaments and filament halves decrease in length by no more than 20% after exposure to and release of 14,000 psi. Bimodal distributions were not observed in equivalent experiments performed on filaments isolated from muscle glycerinated and stored at -20 degrees C for 6 months. Instead, filament dissociation proceeds linearly as a function of increasing pressure. Filaments prepared from muscle glycerinated and stored for 2 and 4 months exhibited pressure-induced behavior intermediate between the filaments prepared from fresh muscle and filaments prepared from muscle stored for 6 months. Since there appears to be no difference in the protein profiles of the various muscle samples, it is possible that stabilization of the native thick filament against hydrostatic pressure arises from trapped ions that are leached out over time.

The effect of high hydrostatic pressure on eukaryotic protein synthesis

The pressure response of two eukaryotic protein synthesizing systems has been characterized. The rabbit reticulocyte system has been tested, both in vivo and in vitro, using endogenous polysomes and polyuridylic acid (poly U). In addition, the poly U-directed polyphenylalanine synthesizing system obtained from wheat germ was utilized. The effect of pressure on eukaryotic protein synthesis has been found to be basically similar to that observed in prokaryotic systems, although the response of the eukaryotic protein synthesizing system is somewhat more complex signifying a greater influence of overlapping reactions. Magnesium was found to affect eukaryotic systems in much the same way as has been reported for prokaryotic systems, i.e., increasing the Mg2+ concentration in a protein synthesizing system increases the barotolerance exhibited by the system. Under conditions of high Mg2+ concentration, however, extreme (up to 160%) stimulation of protein synthesis at lower pressure levels was observed in the eukaryotic systems. Such high stimulation is not apparent in prokaryotic systems. The poly U-directed wheat germ system exhibited the most barotolerant polypeptide synthesis ever seen in our laboratory. This extreme barotolerance was only slightly decreased when the system was tested at reduced concentrations of magnesium.

Role of the 30S ribosomal subunit, initiation factors, and specific ion concentration in barotolerant protein synthesis in Pseudomonas bathycetes

Washed (1 M NH4Cl) ribosomes from Pseudomonas bathycetes, Pseudomonas fluorescens, and Escherichia coli were tested for their ability to synthesize protein or polypeptide at high pressure when used as such, when recombined with homologous initiation factors, and when recombined with heterologous initiation factors. The responses of natural messenger ribonucleic acid (MS-2)-directed systems to pressure were independent of the source of initiation factors and paralleled those of the washed ribosomes in polyuridylate-directed systems. In all cases, the responses to pressure were parallel to those obtained when unwashed ribosomes were utilized; therefore, we concluded that the initiation factors were interchangeable among these organisms, and that these factors did not play a critical role in determining the pressure responses of the protein-synthesizing systems. P. bathycetes ribosomal subunits were isolated under a variety of ionic conditions. These were tested for their ability to synthesize protein and polyphenylalanine at a variety of pressures when used in reconstituted P. bathycetes homologous systems and in hybrid systems with ribosomal subunits from E. coli and P. fluorescens. O. bathycetes 30S subunits, isolated in a buffer solution containing 0 mM NaCl and O mM KC] were functional at any pressure; those isolated in the presence of 150 mM NaCl and 0 mM KCl were functional at 1 atmosphere but barosensitive, and those isolated in the presence of O mM NaCl and 150 mM KCl retained the ion-mediated barotolerance characteristic of crude P. bathycetes ribosome preparations. The 50S subunit remained functional regardless of the method of isolation, and it had no effect on pressure sensitivity.