Biomedical subjects

F Peters

Publications and source records attributed to F Peters.

100 records · Page 6Linked to original sources

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

Ovarian HCG-binding capacity during the oestrous cycle of the rat.

Binding in 125I-labelled HCG to rat ovary varies during the oestrus cycle. The highest amount of binding was found in dioestrous-II rats (7.33 X 10(-15) mol of HCG per mg wet weight), while the lowest binding was observed in oestrous rats (1.67 X 10(-15) mol of HCG per mg wet weight) of circulation LH. It is concluded that the low binding capacity of the rat ovary in the oestrous stage is due to masking of the specific receptors by the excessively high LH hormone secretion in pro-oestrus.

Animals↗

PubMed1977

Binding of human chorionic gonadotrophin to rat ovary during development.

Ovarian tissue of prenatal, newborn, and 5-day-old rats does not specifically bind 125I-labelled HCG. Specific binding of HCG was first observed in ovaries of 10-day-old animals and binding increased with age. These results indicate that, contrary to rat testis, the HCG receptor in the rat ovary is not present during foetal and early postnatal development. Thus, the insensitivity of the ovary to endogenous and exogenous LH or HCG during this developmental period is due to the lack of specific receptors.

Age Factors↗

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↗

PubMed1975

Equivalent and non-equivalent binding sites for tRNA on aminoacyl-tRNA synthetases.

Complexes between tRNAPhe (yeast), tRNASer (yeast) and tRNATyr (Escherichia coli) and their cognate aminoacyl-tRNA synthetases have been studied by sedimentation velocity runs in an analytical ultracentrifuge. The amount of complex formation was determined by the absorption and the sedimentation coefficients of the fast-moving boundary in the presence of excess tRNA or excess synthetase respectively. The same method has been applied to unspecific combinations of tRNAs and synthetases. Inactive material of tRNA or synthetase does not influence the results. 1. Two moles of tRNAPhe can be bound to one mole of phenylalanyl-tRNA synthetase with a binding constant greater than 10(6) M-1. The binding constants for both tRNAs are very similar; the binding sites are independent of each other. Omission of Mg2+ does not prevent binding. 2. Two moles of tRNASer can be bound to one mole of Seryl-tRNA synthetase; the binding of the first and second tRNA is non-equivalent, K1 greater than 10(6) M-1, K2 is determined to be 1.3 X 10(5) M-1 at pH 7.2. Omission of Mg2+ prevents complex formation. 3. Tyrosyl-tRNA synthetase behaves very similarly to seryl-tRNA synthetase. The binding constant for the weakly bound tRNA is 2.3 X 10(5) M-1 at pH 7.2, and 2.5 X 10(6) M-1 at pH 6.0. No complexes are observed in the absence of Mg2+. 4. Unspecific binding was only obtained with phenylalanyl-tRNA synthetase. It binds tRNASer (yeast), tRNAAla (yeast) and tRNATyr (E. coli) with a binding constant about 100 times lower compared to its cognate tRNA. The binding data are discussed with respect to the tertiary structure of the tRNAs, the subunit structure of the synthetases and the possible physical basis for the non-equivalence of binding sites.

Amino Acyl-tRNA Synthetases↗

PubMed1973