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Biomedical subjects

A Parmeggiani

Publications and source records attributed to A Parmeggiani.

At least 127 records · Page 7Linked to original sources
PubMed1981

Properties and regulation of the GTPase activities of elongation factors Tu and G, and of initiation factor 2.

During protein synthesis the interaction with ribosomes of elongation factors Tu (EF-Tu), G (EF-G) and initiation factor 2 (IF-2) is associated with the hydrolysis of GTP which is directly related to the functions of the factors. In this article we review systematically the properties of these GTPase activities in the presence and absence of protein synthesis, and by examining the characteristics of the different minimal systems for the expression of these activities we point to the role of the various effectors and to the enzymological aspects of the systems. For EF-Tu, it has been possible to eliminate any requirement for macromolecular effectors, showing that the factor itself is a GTPase. For EF-G, the presence of at least the 50S ribosomal subunit has remained a requirement, whereas IF-2 needs both the 50S and 30S subunits to exhibit GTPase activity. Between the GTPase activities of the three factors there are some striking similarities, but important differences prevail as a consequence of the specificity of the different functions. This can also be seen by examining the respective ribosomal regions implicated in these reactions. When coupled with protein synthesis, the three GTPase activities reveal characteristics differing from those observed in partial systems.

Anti-Bacterial Agents↗
PubMed1981

Characterization of a kirromycin-resistant elongation factor Tu from Escherichia coli.

The Escherichia coli strain D2216 contains a kirromycin-resistant elongation factor Tu [EF-Tu(D2216); Fischer, E., Wolf, H., Hantke K., & Parmeggiani, A. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 4341-4345]. This stain grows much more slowly than wild-type E. coli strains and contains less than half the amount of EF-Tu. On isoelectric focusing, the whole cell lysate of strain D2216 as well as pure, crystalline EF-Tu(D2216) comprises only a single species indistinguishable from wild-type EF-Tu. In poly(uridylic acid)- [poly(U)] directed poly(phenylalanine) synthesis, enzymatic binding of aminoacyl transfer ribonucleic acid to the ribosome, and susceptibility to trypsin digestion, EF-Tu(D2216) behaves similarly to the EF-Tu from wild-type strains. Kirromycin, which increases the sensitivity to trypsinization of wild-type EF-Tu, has no effect on mutant EF-Tu. In poly(U)-directed poly(phenylalanine) synthesis, partially trypsinized EF-Tu(D2216) displays a 7-fold reduction of its kirromycin resistance as compared to the intact EF-Tu(D2216). This is approximately 300 times less sensitive to the antibiotic than wild-type EF-Tu. The EF-Tu(D2216), purified and crystallized, exhibits a guanosine 5'-triphosphatase activity in the absence of any other physiological effector or kirromycin. This activity is not a contaminant, since it can be selectively stimulated by ribosomes and is inactivated by temperature exactly in the same way as the guanosine 5'-diphosphate binding activity of Ef-Tu(D2216). We conclude that, as consequence of the mutation, the catalytic center of EF-Tu(D2216)-dependent guanosine 5'-triphosphate hydrolysis undergoes spontaneous activation.

Anti-Bacterial Agents↗
PubMed1981

Altered regulation of the guanosine 5'-triphosphate activity in a kirromycin-resistant elongation factor Tu.

In the preceding article a mutant elongation factor Tu (EF-TuD2216) resistant to the action of kirromycin was found to display a spontaneous guanosine 5'-triphosphatase (GTPase) activity, i.e., in the absence of aminoacyl transfer ribonucleic acid (tRNA) and ribosome-messenger RNA. This is the first example of an Ef-Tu supporting GTPase activity in the absence of macromolecular effectors and/or kirromycin. In this study we show that this activity is elicited by increasing NH4+ concentrations. As additional effect, the mutation caused an increased affinity of EF-Tu for GTP. Ammonium dependence of the GTPase activity an increased affinity for GTP are two properties also found with wild-type EF-Tu in the presence of kirromycin [Fasano, O., Burns, W., Crechet, J.-B., Sander, G., & Parmeggiani, A. (1978) Eur. J. Biochem. 89, 557-565; Sander, G., Okonek, M., Crechet, J.-B., Ivell, R., Bocchini, V., & Parmeggiani, A. (1979) FEBS Lett. 98, 111-114]. Therefore, both binding of kirromycin to wild-type EF-Tu and acquisition of kirromycin resistance introduce functionally related modifications. Kirromycin at high concentrations (0.1 mM) does not interact with mutant EF-TuD2216.GDP but still does with EF-TuD2216.GTP in agreement with our previous finding that EF-Tu.GTP is the preferential target of the antibiotic in the wild type [Fasano, O., Bruns, W., Crechet, J.-B., Sander, G., & Parmeggiani, A. (1978) Eur. J. Biochem. 89, 557-565). The GTPase activity of mutant EF-Tu in the presence of aminoacyl-tRNA and ribosome.mRNA is much higher than with wild-type EF-Tu and also much less dependent on the presence of mRNA. Miscoding for leucine, measured as poly(U)-directed poly(phenyl-alanine/leucine) synthesis at increasing Mg2+ concentrations, is identical for both wild-type and mutant EF-Tu.

Ammonia↗
PubMed1980

[Clinical and therapeutic studies of pancreatitis].

The literature on the medical management of pancreatitis is reviewed. Reference is made to successful results obtained in 30 personal cases with a semimedicamentous protocol, in which an antipancreatitic activity in the true sense was obtained by administering aprotinine and glucagon. Eight subjects presented acute or recrudescent chronic forms, 12 pancreatitis combined with cholelithiasis, 5 secondary forms following penetrating duodenal ulcers, and 5 forms arising after stomach, duodenal or bile duct surgery. The evaluation of each case is described and the conclusion is drawn that intensive, timely medical therapy will secure resolution in the majority of cases.

Adult↗
PubMed1980

The coupling with polypeptide synthesis of the GTPase activity dependent on elongation factor G.

The coupling with polypeptide synthesis of the ribosome-elongation factor G (EF-G)-dependent GTPase activity was studied in a highly purified system with well characterized NH4Cl-washed ribosomes which were from 55 to 67% active in poly(U)-directed polyphenylalanine synthesis. The lowest stoichiometries of total GTP hydrolysis to polyphenylalanine incorporation (2.4 to 2.8) were observed at concentrations of MgCl2 (4 to 6.5 mM) slightly lower than the Mg2+ optimum for polyphenylalanine synthesis (7 to 8 mM), in a system containing 80 mM NH4Cl or KCl. For minimal stoichiometry, the concentration of EF-G should be rate-limiting, whereas that of EF-T (EF-Tu.EF-Ts) and aminoacyl-tRNA should be in excess, since the coupling of the EF-G GTPase activity depends on ribosomes in pretranslocative state. Under this condition, the apparent Km values for GTP of GTPase activity and polyphenylalanine synthesis are identical, and they are about an order of magnitude lower than the Km of the ribosome-EF-G-dependent GTPase activity uncoupled from polypeptide synthesis. The stoichiometry was calculated without the usual correction fro GTP hydrolysis obtained in the same system lacking elongation factor T or aminoacyl-tRNA. Such a correction causes overestimation of the uncoupled EF-G GTPase activity still present in the complete system, leading to artificially low stoichiometric values.

GTP Phosphohydrolase-Linked Elongation Factors↗
PubMed1980

Interaction of elongation factor Tu with the ribosome. A study using the antibiotic kirromycin.

Elongation factor Tu (EF-Tu) dependent GTP hydrolysis normally requires the presence of ribosomes and aminoacyl-tRNA (aa-tRNA). In the presence of the antibiotic kirromycin, the factor alone displays a GTPase activity that is enhanced by ribosomes and/or aa-tRNA [Wolf, H., Chinali, G., & Parmeggiani, A. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 4910-4914]. Using this system, we have found the following: (1) the 50S ribosomal subunit can substitute the 70S ribosome; (2) the 50S CsCl core a, b, and c particles [Sander, G., Marsh, R. C., Voigt, J., & Parmeggiani, A. (1975) Biochemistry 14, 1805-1814], lacking an increasing number of proteins, can induce ca. 65, 45, and 25%, respectively, of the EF-Tu-kirromycin GTPase activity of control 50S subunits, in the presence of 30S subunits and aa-tRNA; (3) addition of proteins L7/L12 with L10, but not of proteins L7/L12 free from L10, restored the activity of all the 50S CsCl cores in the EF-Tu-kirromycin-dependent GTPase to 70-90% of the control; (4) proteins L7/L12, with or without contaminating L10, did not induce any EF-Tu-dependent GTPase activity, in contrast to a recent report [Donner, D., Villems, R., Liljas, A., & Kurland, C. G. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 3192-3195], whether EF-Ts and/or kirromycin were present or not.

GTP Phosphohydrolase-Linked Elongation Factors↗
PubMed1980

Clinical course of ulcerative colitis in Italy.

The prognosis of ulcerative colitis has been studied in 122 patients with this disease who had been referred to Bolgna from various parts of Italy and were then followed up. The overall mortality rate was 4.9% and the percentage of patients who were treated by total colectomy was 15.5%. Postoperative mortality was 10.5%, and the percentage of patients who developed carcinoma of the colon was 0.8%. All these figures fall within the range of values for the relevant variables quoted by previous authors from different countries. It is concluded that the prognosis of ulcerative colitis in the 122 Italian patients in the present study was similar to that reported previously in patients of other nationalities.

Animals↗
PubMed1977

[Parietal cell vagotomy (PCV): the treatment of choice of duodenal ulcer].

Gastric resection or vagotomy plus drainage are not easy alternatives for the treatment of duodenal ulcer. More complications are met after resection, more relapses after vagotomy, whereas the postoperative sequelae are the same for both operations. Vagotomy of the parietal cells is designed to prevent all such sequelae by leaving the innervation of the antrum intact so that drainage can be omitted. Experience has so far shown that very few complications occur, whereas severe and slight dumping and diarrhoea are virtually eliminated. Gastric emptying times are slightly affected (a little longer for solids and a little quicker for fluids), but drainage in non-stenosing cases of duodenal ulcer is not necessary. The true average incidence of recurrences after this operation cannot yet be determined, since the results of the published series vary considerably. This may be due to the continuous progress being made in the development of the surgical technique. Random studies comparing this operation with other forms of duodenal management are urgently required. It is, of course, essential for surgeons practising the new operation must, as in the case of other delicate surgial procedures, to receive a proper training at specialised centres.

Animals↗