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Biomedical subjects

G Maass

Publications and source records attributed to G Maass.

At least 127 records · Page 7Linked to original sources
PubMed1978

[Visualization by electronmicroscopy of 28 nm virusparticles (astroviruses) in faeces of newborns with acute nonbacterial gastroenteritis (author's transl)].

On occasion of an epidemic of acute nonbacterial gastroenteritis virus particles were visualized by electronmicroscopy in the faeces of 76 newborns; these particles had the following properties: mean diameter 28 nm; ether-resistent, stable at pH 3.0; buoyant density 1.33--1.34 g/ml in CsCl. About 10% of these particles had a definite star-like structure on their surface. Due to these properties the virusparticles were considered to be astroviruses. The virus was not cytopathogenic for cell cultures susceptible for enteroviruses, and not pathogenic for newborn mice.

Cytopathogenic Effect, Viral↗
PubMed1977

[Viruses as causal agents of gastroenteritis in infants and young children (author's transl)].

Electron microscopic examination of stool samples from 195 infants and young children with acute gastroenteritis revealed rota virus in 31 samples (= 16%), corona virus in 44 samples (= 23%) and adenovirus in 13 samples (= 7%). Viruses were excreted for between 4 and 8 days in patients infected with rota virus and corona virus respectively. An outbreak of acute gastroenteritis in a premature baby unit with 24 cases is reported: corona virus was found in the stools of 15 infants. It is suggested that corona virus as well as rota virus may cause gastroenteritis in infants and small children.

Acute Disease↗
PubMed1977

Fluoresceinylthiocarbamyl-tRNATyr: a useful derivative of tRNATyr (E.coli) for physicochemical studies.

Fluoresceinylthiocarbamyl-tRNATyr (FTC-tRNATyr) is prepared from tRNATyr and fluoresceinisothiogyanate (FITC) under mildly alkaline conditions. Labelling occurs specificly at the base Q of tRNATyr. The modified tRNA is fully active in the aminoacylation assay; when aminoacylated it is recognized by the elongation factor Tu (EF-Tu). Codon-anticodon interaction, however, is severely affected by the modification.

Anticodon↗
PubMed1977

Mechanism of tRNA-synthetase recognition: role of terminal A.

The function of the terminal A of tRNA Phe (yeast) with respect to complex formation with the cognate aminoacyl-tRNA synthetase has been studied using equilibrium and fast kinetic techniques. Removal of the terminal A influences the equilibrium parameters of the tRNA-synthetase interaction only slightly, the mechanism of complex formation, however, is changed significantly. The binding mechanism of unmodified tRNAPhe comprises a recombination step and a consecutive conformational change. In contrast, the reaction between tRNAPheCC and the cognate synthetase is characterized by a simple one step mechanism. It is concluded that the terminal A is responsible for the occurrence of the conformational change of the tRNA-synthetase complex. The conformational change is interpreted as a proper alignment of the terminal A of the tRNA to the active site of the synthetase.

Adenine↗
PubMed1977

Ternary complex formation between elongation factor Tu, GTP and aminoacyl-tRNA: an equilibrium study.

The equilibria between the elongation factor Tu-GTP complex (EF-Tu-GTP) from Escherichia coli and tyrosyl-tRNATyr from E. coli as well as phenylalanyl-tRNAPhe and seryl-tRNASer from yeast were studied using a novel procedure, which takes advantage of the protective effect of ternary complex formation on the stability of theaminoacyl bond against non-enzymatic hydrolysis. At 25 degrees C and at pH 7.4 tyrosyl-tRNATyr, phenylalanyl-tRNAPhe and seryl-tRNASer are bound with binding constants of 0.7 X 10(7) M-1, 5.0 X 10(7) M-1 and 0.5 X 10(7) M-1 respectively. The binding of aminoacyl-tRNA to EF-Tu-GTP has a negative deltaH of the order of 10 kcal/mol (42 kJ/mol). Complex formation is dependent on ionic strength: with 0.1 M KCl Kass = 0.8 X 10(7) M-1, with 0.5 M KCl Kass = 0.2 X 10(7) M-1 was determined for the binding of Tyr-tRNATyr.

Calorimetry↗
PubMed1977

[Seroepidemiological Investigations on the epidemiology of human rotavirus infections (author's transl)].

263 sera of infants and children up to 10 years of age were tested for antibodies (CF-test) against Nebraska calf diarrhoea virus (NCDV) which is antigenically related to the rotavirus of man; in addition the mean antibody titers in different age groups were investigated. Antibodies of maternal origin were eliminated during the first year of life. Most of the infections occurred during the second year of life and at the end of this year 40-50% of the investigated children demonstrated antibodies against NCDV; this frequency persists during the rest of the investigated life period.

Antibodies, Viral↗
PubMed1976

[Electronmicroscopic visualization of virusparticles in cases of gastroenteritis of infants and children (author's transl)].

In 72 faecal extracts examined from babies and infants with an acute gastroenteritis, virus particles were found in 29 cases. These particles could be classified as reovirus-like in 16 cases, coronaviruses in 11 cases and adenoviruses in 2 cases. The electron microscopic investigation of 11 faecal extracts from healthy babies did not show any of these particles. Comparative studies on the concentration methods were performed.

Acute Disease↗
PubMed1976

Effect of excision of the Y-base on the interaction of tRNAPhe (yeast) with phenylalanyl-tRNA synthetase (yeast).

The interaction between tRNAPhe (yeast), from which the Y-base has been removed by acid treatment, and phenylalanyl-tRNA synthetase (yeast) has been investigated by fluorescence competition titrations and sedimentation velocity runs. The binding parameters are given under various ionic conditions. The tRNAPhe-Y still can occupy the specific binding sites on the enzyme. Compared to unmodified tRNAPhe, the binding constant is lowered by more than one order of magnitude. It can be concluded that the Y-base is not necessary for specific recognition of tRNAPhe by the cognate synthetase, it rather may represent a point of attachment for the synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Distinct steps in the specific binding of tRNA to aminoacyl-tRNA synthetase. Temperature-jump studies on the serine-specific system from yeast and the tyrosine-specific system from Escherichia coli.

The kinetics of the interaction of tRNASer and seryl-tRNA synthetase from yeast as well as of tRNATyr and tyrosyl-tRNA synthetase from Escherichia coli have been investigated by temperature-jump experiments. It could be shown that complex formation proceeds in two distinct steps. This was demonstrated for both the first and the second binding site. The two-step mechanism was deduced from the characteristic concentration dependence of the relaxation times. Seryl-tRNA synthetase recombines with the first tRNA to form an intermediate complex (kI12, kI21), which is transformed in a fast reaction to the final 1:1 complex (kI23, kI32). At pH 7.2 with 0.1 M KCl the rate constants are: kI12 = 2.7 X 10(8) M-1 S-1; kI23, kI32). At pH 7.2 with 0.1 M KCl the rate constants are: kI12 = 2.7 x 10(8) M-1 S-1; kI21 = 220 S-1; kI23 = 760 S-1; kI32 = 330 S-1. The 1:1 complex can bind a second tRNA. At pH 7.2 without added salt the rate constants are: KII2 = 0.9 X 10(8) M-1 S-1; kII21 = 270 S-1; kII23 = 120 S-1; kII32 = 1250 S-1. The tyrosine-specific system behaves very similarly to the serine-specific system. Data are given for pH 7.2 (pH 6.0) for the binding of the second tRNA: kII12 = 1 X 10(8) (2.5 X 10(8)) M-1 S-1; kII21 = 470 (170) S-1; kII23 = 150 (530) S-1; kII32 = 1540 (720) S-1. The kinetic results are discussed in terms of their relevance to the recognition process and their relation to the anticooperative binding behaviour of tRNA to synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Mechanism of discrimination between cognate and non-cognate tRNAs by phenylalanyl-tRNA synthetase from yeast.

The interaction between phenylalanyl-tRNA synthetase from yeast and Escherichia coli and tRNAPhe (yeast), tRNASer (yeast), tRNA1Val (E. coli) has been investigated by ultracentrifugation analysis, fluorescence titrations and fast kinetic techniques. The fluorescence of the Y-base of tRNAPhe and the intrinsic fluorescence of the synthetases have been used as optical indicators. 1. Specific complexes between phenylalanyl-tRNA synthetase and tRNAPhe from yeast are formed in a two-step mechanism: a nearly diffusion-controlled recombination is followed by a fast conformational transition. Binding constants, rate constants and changes in the quantum yield of the Y-base fluorescence upon binding are given under a variety of conditions with respect to pH, added salt, concentration of Mg2+ ions and temperature. 2. Heterologous complexes between phenylalanyl-tRNA synthetase (E. coli) and tRNAPhe (yeast) are formed in a similar two-step mechanism as the specific complexes; the conformational transition, however, is slower by a factor 4-5. 3. Formation of non-specific complexes between phenylalanyl-tRNA synthetase (yeast) and tRNATyr (E. coli) proceeds in a one-step mechanism. Phenylalanyl-tRNA synthetase (yeast) binds either two molecules of tRNAPhe (yeast) or only one molecule of tRNATyr (E. coli); tRNA1Val (E. coli) or tRNASer (yeast) are also bound in a 1:1 stoichiometry. Binding constants for complexes of phenylalanyl-tRNA synthetase (yeast) and tRNATyr (E. coli) are determined under a variety of conditions. In contrast to specific complex formation, non-specific binding is disfavoured by the presence of Mg2+ ions, and is not affected by pH and the presence of pyrophosphate. The difference in the stabilities of specific and non-specific complexes can be varied by a factor of 2--100 depending on the ionic conditions. Discrimination of cognate and non-cognate tRNA by phenylalanyl-tRNA synthetase (yeast) is discussed in terms of the binding mechanism, the topology of the binding sites, the nature of interacting forces and the relation between specificity and ionic conditions.

Amino Acyl-tRNA Synthetases↗
PubMed1975

Tertiary structure of tRNAPhe (yeast): kinetics and electrostatic repulsion.

Conditions were established that allowed the observation of the unfolding of the tertiary structure of tRNAPhe (yeast) without the interference of either secondary structure or low salt aberrant structures. Relaxation kinetics of tertiary structure melting show that the reaction proceeds according to co-operative all-or-none mechanism. The negative activation enthalpy of formation (delta H+ + R = -14 +/- 5 kcal/mol, -59 +/- 21 kJ/mol) implies a fast pre-equilibrium preceding the rate-limiting step. The ionic strength dependence of the corresponding rate constant demonstrates that most of the electrostatic repulsion characteristic of tertiary structure folding is overcome before the rate-limiting step is reached. On the other hand, most of the stabilizing enthalpy change occurs after the rate-limiting step. At the usual ionic strength (0.1 M Na+) tertiary structure folding is about 100 times slower than double-helix formation. Extrapolation of the rate constants to high ionic strengths, however, indicates that the dynamic differences between secondary and tertiary structure are only due to electrostatic repulsion. The stabilization of tertiary structure by alkaline salts is increased by decreasing the cationic radius. Double helices show virtually no dependence on the radius of monovalent cations. This indicates considerable geometric restrictions for the stabilization of tertiary structure.

Kinetics↗
PubMed1975

Kinetics of conformational changes in tRNA Phe (yeast) as studied by the fluorescence of the Y-base and of formycin substituted for the 3'-terminal adenine.

The kinetics of the melting transitions of tRNA Phe (yeast) were followed by the fluorescence of the Y-base and of formycin substituted for the 3'-terminal adenine. As judged from differential UV absorbance melting curves the formycin label had virtually no influence on the conformation of the tRNA. A temperature jump apparatus was modified to allow the simultaneous observation of transmission and fluorescence intensities by two independent optical channels. The design of a temperature jump cell with an all quartz center piece is given. The cell is resistant to temperatures up to 90 degrees C; it provides high optical sensitivity, low stray light intensity and the possibility of measuring fluorescence polarization. The T-jump experiments allowed to discriminate between fast unspecific fluorescence quenching (r less than 5 musec) and slow cooperative conformational changes. In the central part of the temperature range of UV-melting (midpoint temperature 30 degrees C in 0.01 M Na+ and 39 degrees C in 0.03 M Na+, pH 6.8) two resolvable relaxation processes were observed. The corresponding relaxation times were 20 msec and 800 msec at 30 degrees C in 0.01 M Na+, and 4 msec and 120 msec at 39 degrees C in 0.03 M Na+. The Y-base fluorescence shows both of the relaxation effects, which almost cancel in equilibrium fluorescence melting, because their amplitudes have opposite signs. From this finding the existence of some residual tertiary structure is inferred which persists after the unfolding of the main part of tertiary structure during early melting (midpoint temperature 24 degrees C in 0.03 M Na+). In the fluorescence signal of the formycin also the two relaxation effects appear. Both of them are connected with a decrease of the fluorescence intensity. From the results a coupled opening of the anticodon and acceptor branches is concluded.

Adenine↗
PubMed1975

[Perinatal psychohygienics -- importance and chance of a primary preventive medicine by the gynaecologist (author's transl)].

Qualitative or quantitative deficiency of maternal "primary love" in the critical period of the first years of life very often leads in later years of life to severe psychosomatic disorders or psychopathologic states as depression, suicide, addiction, criminality, social disorders and psychosis. A Preventive Care Passport with a date program for the pregnant woman and young mother and a standardized program for the gynaecologist is proposed in connection with all necessary perinatal preventive methods and integration of psychohygienic investigation and treatment. Perinatal psychohygienics could be practiced by questionnaires to find out maternal pathogenic conflicts, by social workers in order to avoid unnecessary maternal work in the first years of her child's life and group discussions after a 16-mm-film or an information paper about the normal psychic development of a child. Further tasks are granting the presence of the father at childbirth "rooming-in" with "self-demand", early adoption within the first eight weeks of life, group discussions of parents about conflicts with their children, hospitalization of infants -- only in cases of vital indication -- together with their mother and psychological preparing for medical manipulations and social benefits for the young mother or parents. The recommendations of the WHO for the application of psychohygienics could be integrated in this program.

Child, Preschool↗