Biochemical applications of a synchronously pumped krypton ion dye laser fluorescence system.

A synchronously pumped krypton ion dye laser fluorescence system is shown to provide tunable, polarized, subnanosecond pulses at high repetition rates, modest peak powers, and low energy. Such a source is uniquely suited to fluorescence investigations of biochemical mechanisms. Applications of this fluorescence excitation source to analysis, life-time determination, and depolarization effects are discussed.     

Escherichia coli CAN lacks a tRNA-processing nuclease.

Escherichia coli strain CAN is unable to support the growth of bacteriophage T4 strains requiring the suppressor function of T4 tRNASer. Biochemical analysis of the mutant strain revealed that it is deficient in a RNase which acts on the artificial tRNA precursor tRNA-C-U.     

Metabolite-sensitive, ATP-dependent, protein kinase-catalyzed phosphorylation of HPr, a phosphocarrier protein of the phosphotransferase system in gram-positive bacteria

In this review article we summarize the recent information available concerning important mechanistic and physiological aspects of the protein kinase-mediated phosphorylation of seryl residue-46 in HPr, a phosphocarrier protein of the phosphoenolpyruvate: sugar phosphotransferase system in Gram-positive bacteria. Emphasis is placed upon the information recently obtained in two laboratories through the use of site-specific mutants of the HPr protein. The results show that (i) in contrast to eukaryotic protein kinases, the HPr(ser) kinase recognizes the tertiary structure of HPr rather than a restricted part of the primary sequence of the protein; (ii) like seryl protein kinases of eukaryotes, the HPr(ser) kinase can phosphorylate a threonyl residue, but not a tyrosyl residue when such a residue replaces the regulatory seryl residue in position-46 of the protein; (iii) the regulatory consequences of seryl phosphorylation are due to the introduction of a negative charge at position-46 in the protein rather than the bulky phosphate group; and (iv) PTS protein-HPr interactions influence the conformation of HPr, thereby retarding or stimulating the rate of kinase-catalyzed seryl-46 phosphorylation. The physiological consequences of HPr(ser) phosphorylation in vivo are still a matter of debate.     

A role for lipids in the functional and structural properties of the rat liver aminoacyl-tRNA synthetase complex

The high molecular weight aminoacyl-tRNA synthetase complexes found in extracts of many eukaryotic cells often contain lipids and other non-protein components. Since hydrophobic interactions play an important role in maintaining synthetases in the complex, it has been suggested that the lipids present may also participate in its functional and structural integrity. In order to learn more about the role of lipids in the complex, we have compared the properties of the normal complex to one which has been delipidated by treatment with Triton X-114. Delipidation does not affect the size or activity of the aminoacyl-tRNA synthetase complex, but a variety of functional and structural properties of individual synthetases in the complex are altered dramatically. These include sensitivity to salts plus detergents, temperature inactivation, hydrophobicity, and sensitivity to protease digestion. In the latter case, removal of lipids also affects the low molecular weight products released by protease digestion. Purification of the synthetase complex by various chromatographic procedures can remove the lipids and lead to a structure that behaves like the delipidated complex prepared by detergent treatment. The significance of these findings for the intracellular location of aminoacyl-tRNA synthetases and for the study of purified complexes are discussed.     

Amino acid sequence of the amphiphilic phosphocarrier protein factor IIILac of the lactose-specific phosphotransferase system of Staphylococcus

The lactose-specific factor III of the phosphotransferase system of Staphylococcus aureus is an amphiphilic trimeric protein composed of identical subunits. It is hydrophilic in its unphosphorylated state and can be isolated from the cytoplasmic protein fraction. It becomes a constituent of the membrane-bound phosphotransferase complex upon phosphorylation of a single histidyl residue. The sequence of S. aureus factor IIILac was determined and revealed that the subunits consist of 103 residues corresponding to a Mr of 11 367 and of 34 101 for the native trimer: (sequence; see text) According to this sequence and previous work histidine residue 82 located in the C-terminal part of the polypeptide chain is phosphorylated at the N-3 position by phosphoenolpyruvate, enzyme I, and histidine-containing phosphocarrier protein. The N-terminal part of the protein comprising approximately one-third of the chain exhibits in vitro affinity toward membrane-bound enzyme IILac.     

Purification and characterization of Escherichia coli RNase T

RNase T, a nuclease thought to be involved in end-turnover of tRNA, has been purified about 4,000-fold from extracts of Escherichia coli. At this stage of purification, the enzyme was judged to be at least 95% pure based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native molecular weight of RNase T determined from gel filtration and sedimentation analyses is about 50,000, whereas the monomer molecular weight determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis is 25,000, suggesting that the protein is an alpha 2 dimer. Purified RNase T is extremely sensitive to inactivation by oxidation, sulfhydryl group reagents, and temperature. The ribonuclease activity against tRNA-C-C-[14C]A is optimal at pH 8-9 in the presence of 2-5 mM MgCl2 and ionic strengths of less than 50mM. Although RNase T is highly specific for intact tRNA-C-C-A as a substrate and can hydrolyze all species in a mixed population of tRNA, it is inhibited by other RNAs, such as poly(A), rRNA, 5 S RNA, and tRNA-C-C. RNase T is an exoribonuclease which initiates attack at a free 3' terminus of tRNA and releases AMP; aminoacyl-tRNA is not a substrate. The role of RNase T in the end-turnover of tRNA and its possible involvement in other aspects of RNA metabolism are discussed.     

Phosphoenolpyruvate-dependent phosphorylation of a 55-kDa protein of Streptococcus faecalis catalyzed by the phosphotransferase system

Abstract A protein with an M _r of 55000 was isolated from glucose-grown Streptococcus faecalis cells. The protein becomes phosphorylated in a phosphoenolpyruvate-dependent reaction catalyzed by enzyme I and HPr of the bacterial phosphotransferase system. It did not stimulate phosphoenolpyruvate-dependent glucose phosphorylation. Several sugars were tested for their ability to dephosphorylate the phosphorylated protein in the presence of membrane fragments. Even though some of the sugars were able to dephosphorylate phospho-HPr quickly, the factor III-like 55-kDa protein remained phosphorylated. We therefore assumed that this protein is not involved in any sugar uptake reaction but that it exerts a regulatory function in Gram-positive bacteria comparable to the function of factor III specific for glucose in Escherichia coli .     

Purification and properties of 1-phosphofructokinase from Escherichia coli

Abstract The thermophilic facultatively phototrophic green bacterium Chloroflexus aurantiacus strain Ok-70-fl was shown to possess sulfide-repressed hydrogenase activity. Biosynthesis of the enzyme was severely repressed by S²⁻ (5.7 mM) and stimulated specifically by Ni²⁺ and by molecular hydrogen. The hydrogenase was shown to be localized in the cytoplasmic membrane and could be solubilized from the latter by the detergent Triton X-100 in a state forming one enzymatically active band ( M _r 170 × 10³) in polyacrylamide gels. In the membraneous state, the hydrogenase had its maximal activity at 73°C and was active with methyl viologen, methylene blue, menadione and flavins, but not with NAD or NADP as electron acceptors. Solubilization of the enzyme with Triton X-100 resulted in a drastic increase in the FAD/FMN-linked activity.