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Biomedical subjects

M Libonati

Publications and source records attributed to M Libonati.

At least 55 records · Page 3Linked to original sources
PubMed1980

Ionic control of enzymic degradation of double-stranded RNA.

The pattern of the degradation of various double-stranded polyribonucleotides by several ribonucleases (bovine RNAase A and its cross-linked dimer, bovine seminal RNAase, and pike-whale pancreatic RNAase) has been studied as a function of ionic strength and pH. It appears that (1) there is no direct correlation between the secondary structure of double-stranded RNA and its resistance against enzymatic breakdown, i.e., the stability of the secondary structure of double-helical RNA is not the main variable in the process. (2) The acstivity responses of the enzymes examined to changes of ionic strength and pH suggest that enzymic degradation of double-stranded RNA is mainly controlled by ion concentration, and that the process may fall within the phenomena interpreted by the theory of the ionic control of biochemical reactions advanced by Douzou and Maurel (Douzou, P. and Maurel, P. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 1013--1015). (3) The activity curves of the enzyme studied show, at a given pH, a shift toward higher ionic strengths as a function of the basicity of the enzyme protein. This finding explains the already observed correlation between number and/or density of positive charges of a ribonuclease molecule and its ability to attack double-stranded RNA in 0.15 M sodium chloride/0.015 M sodium citrate (SSC). (4) A careful analysis of the influence of ionic strength and pH on the reaction appears to be necessary in order to characterize a ribonuclease which shows activity towards double-stranded RNAs, and to allow a meaningful comparison between different enzymes capable of attacking these substrates.

Endonucleases↗
PubMed1980

Double-stranded RNA.

High molecular weight, fully double-stranded RNA (dsRNA) has been recognized as the genetic material of many plant, animal, fungal, and bacterial viruses (Diplornaviruses): virusspecific dsRNA is also found in cells infected with single-stranded RNA viruses. DsRNA has identified in a variety of apparently normal eucaryotic cells and is associated with the "killer" character of certain strains of Saccaromyces cerevisiae.

Animals↗
PubMed1979

[Analysis of deoxyribonuclease I and II activity as a function of ionic strength and pH].

The action of deoxyribonucleases I and II has been studied as a function of ionic strength and pH, in the light of the theory of the ionic control of biochemical reactions (P. Douzou and P. Maurel (1977) Proc. Nat. Acad. Sci. USA, 74, 1013-1015). The pattern of DNA degradation by the two enzymes fits the general principles of the theory. However, the activity of DNAase II, a dimeric, basic protein (pI = 10,2) appears to be scarcely modulated by variables such as ionic strength and pH. This is reminiscent of what was elsewhere observed with the system double stranded RNA-seminal RNAase (also a very basic, dimeric enzyme), and could, therefore, tentatively be correlated with the dimeric and/or the very basic nature of the enzyme protein.

Animals↗
PubMed1979

[DNA-protein interactions. Destabilizing activity of sheep pancreatic RNAase].

Evidence is presented that ovine pancreatic ribonuclease, a protein strictly homologous to bovine RNAase A but with one positive charge less, has a definite 'destabilizing' activity (quite similar to that of the bovine enzyme) on double-stranded DNA. This action of sheep pancreas RNAase has been measured by differential spectrophotometry and determining the thermal-transition profiles of the protein-DNA complexes.

Animals↗
PubMed1978

How much is secondary structure responsible for resistance of double-stranded RNA to pancreatic ribonuclease A?

1. Double-stranded f2 sus11 or Qbeta RNAs, resistant to bovine pancreatic RNAase A in 0.15 M NaCl/0.015 M sodium citrate (SSC), are quickly and completely degraded at 10-fold lower ionic strength (0.1 X SSC) under otherwise similar conditions. At this ionic strength the secondary structure of double-stranded RNA is maintained, as judged by the following: (a) the unchanged resistance of double-stranded RNA and DNA, under similar low ionic strength conditions, to nuclease S1 from Aspergillus oryzae, in contrast with the sensitivity of the corresponding denatured nucleic acids to this enzyme, specific for single-stranded RNA and DNA; (b) the co-operative pattern of the thermal-transition profile of double-stranded RNA (with a Tm of 89 degrees C) in 0.1 X SSC. 2. Whereas in SSC bovine seminal RNAase (RNAase BS-1) and whale pancreatic RNAase show an activity on double-stranded RNA significantly higher than that of RNAase A, in 0.1 X SSC the activity of the latter enzyme on this substrate becomes distinctly higher than that of RNAase BS-1, and similar to that of whale RNAase. 3. From these results it is deduced that the secondary structure is probably not the only nor the most important variable in determining the susceptibility double-stranded RNA to ribonuclease. Other factors, such as the effect of ionic strength on the enzyme and/or the binding of enzyme to nucleic acids, may play an important role in the process of double-stranded RNA degradation by ribonucleases specific for single-stranded RNA.

Aspergillus oryzae↗
PubMed1977

Differential, structure-dependent susceptibility of poly(A) and RNA to monomeric and dimeric pancreatic ribonuclease A.

Cross-linked dimers of bovine RNAase A are definitely more efficient than monomers at degrading polyadenylic acid under conditions of ionic strength and pH, where the polymer assumes either a double-helical or an ordered single-stranded, base-stacked structure. The opposite occurs, i.e., monomers of RNAase A are definitely more active than dimers,when poly(A) is digested by the two enzyme species under conditions where the conformation of the polymer is essentially that of a random coil. The same pattern of events occurs when total RNA from Escherichia coli or single-stranded RNA of f2 sus11 bacteriophage are used as substrates under opposite ionic-strength conditions. In the presence of high salt concentrations, favouring the formation and the stability of a secondary structure in self-complementary sequences of RNA, the ribonucleic acids are degraded at a higher rate by dimers than by monomers of bovine RNAase A. The opposite occurs in the presence of very low salt concentrations, i.e. when the RNAs are in solution presumably as random coils. These observations are discussed in the light of a hypothesis already advanced to understand the mechanism of enzymic degradation of secondary structures of polyribonucleotides.

Animals↗
PubMed1976

Proteolytic enzymes as structural probes for ribonuclease BS-1.

Trypsin, pepsin and subtilisin have been used as conformational probes for the structure of bovine seminal ribonuclease BS-1 by studying, under definite conditions, their effects on the seminal enzyme, a dimeric protein made up to two identical subunits; on bovine pancreatic monomeric ribonuclease A (EC 3.1.4.22) with a polypeptide chain homologous to that of the seminal ribonuclease subunit chain; and on a monomeric, active and stable derivative of seminal ribonuclease. The results show: (1) that the C-terminal regions of the pancreatic and the seminal proteins are very similar as they appear to fit in an identical way to the active site of pepsin; (2) that the resistance of the N-terminal region of ribonuclease BS-1 to subtilisin is not due to the dimeric structure of the protein, but to the conformation of this region, where an essential feature is the presence of a proline residue at position 19; (3) that the monomer of ribonuclease BS-1 is resistant to tryptic action only when bound to the partner monomer in the quaternary structure of the protein. This indicates that dissociation of the seminal ribonuclease makes some potentially susceptible susceptible bond or bonds available to trypsin either through a conformational change of the protein subunit, or by simply exposing the protein area hidden at the intersubunit interfaces.

Animals↗
PubMed1975

Degradation of double-stranded RNA by a monomeric derivative of ribonuclease BS-1.

Double-stranded RNA, resistant to the action of pancreatic monomeric RNAase A, is actively degraded by seminal dimeric RNAase BS-1. Evidence is presented that a monomeric derivative of seminal RNAase degrades double-stranded RNA as efficiently as the parent dimeric molecule. This finding is discussed in the light of the hypothesis previously advanced that two active sites simultaneously available on an enzyme molecule may be responsible for degradation of double-stranded polyribonucleotides.

Animals↗
PubMed1975

The use of haloperidol for treatment of postoperative nausea and vomiting--a double-blind placebo-controlled trial.

Sixty-two postoperative patients were admitted to a double-blind study to compare the therapeutic effectiveness of a single intramuscular injection of 1 mg of haloperidol with that of a placebo for the relief of vomiting and nausea following surgical procedures. Significantly fewer patients continued to vomit or experience nausea in the haloperidol-treatment group than in the placebo-treatment group. No statistically or clinically significant change in vital signs occurred in the haloperidol-treatment group. No serious side effect occurred in either group.

Abdomen↗