S U M M A R YMagsat data have been used to design scalar magnetic anomaly maps in an area that covers about half of Europe on both sides of the north-south directed European Geotraverse (EGT). The two maps refer to different altitudes and are intended to place recent compilations of aeromagnetic surveys along the EGT (Wonik er af. 1992) into global perspective.The presentation of the magnetic anomalies and their compatibility with the aeromagnetic data required (i) a suitable reference field for subtraction from the measured total field, which was derived from the field model M102089 by Cain, and (ii) a proper function of time reduction to the epoch 1980.0, which has been obtained from the actual satellite data. Because of the considerable noise in the data only those anomalies have been chosen for mapping, which show up in all Magsat tracks independent of altitude and epoch of measurement. The anomaly maps are based upon the less disturbed dawn track data, but a few dusk tracks have also been used as tie lines.The anomalies are interpreted in terms of a magnetization model, which divides the Earth's lithosphere in Europe into blocks of extension 1"N-S by 2"E-W and attributes to each block the 'Depth Integrated Magnetization' of the magnetized layer, i.e. the magnetization integrated over the vertical extension of the block. Each block is represented by a dipole parallel to the inducing core field, and the calculated model field is adjusted to the anomaly maps by trial and error, starting with an initial coarse distribution that seems plausible from the anomalies and from local geomagnetic surveys. For a realistic model field in the EGT area a rather large portion of the Earth's magnetized lithosphere outside the area under investigation must be included in the calculation.In order to check, whether the features of the magnetization model are necessary for the interpretation of the field anomalies, they are compared with the distribution of magnetization that is obtained by the application of linear inverse theory.Prominent features of the model of crustal magnetization are the contrast between high values over the East European Platform and low values in the younger parts of Europe, maxima at the iron ore districts of Kiruna and Kursk, a broad minimum centred at St Petersburg, and only small differences between the Mediterranean Sea and the adjacent continental areas. There is a fairly good agreement of these anomaly maps with the corresponding maps presented by Cain er af. (1989a).
The interaction between p-guanidmobenzoate-trypsinogen and the isoleucine-valine dipeptide has been investigated by temperature-jump relaxation spectrometry. Using the absorbance at 281 nm the concentration dependence of the relaxation parameters is consistent with the conventional induced-fit model: rapid ligand bindin, u coupled to a slower intramolecular change; some alternative mechanisms can be excluded. At 296 R, 0.1 M Tris HCI, pH = 7.4, the dissociation equilibrium constant for the overall process isK = zS.l(iO.2) X 16' hl; for the binding step Kt = 2_3(%0.3) X lob3 hl and the rate constants for the structural change are k2 = 26(~6)s-' and k, = 0.6 l(? 0.04)s-' ; the overall dissociation reaction enthalpy is aHo = 26(*6) kJmoT' and the reaction entropy is AS0 = 4(+20) kJiT-' mol-'. In combination with CD and X-ray crystallographic data, the results of this study suggest that the binding of the dipeptide to a trypsinogen-like, partially disordered conformation induces a transition to a trypsin-like highly ordered structure. I_ IntroductionThe regulation of enzymatic activity by limited proteolysis of zymogens is a well known bioiogical control device; however, the mechanism of the conversion from the inactive form of the protein to the catalytically active species usually is not known in detail. In the case of bovine trypsinogen, X-ray crystallographic analysis has suggested that the formation of active trypsin is a transition of a partially disordered protein to a highly ordered structure The relaxation kinetic data presented here provide evidence that the dipeptide binds predominantly to the partially disordered protein and subsequently induces a slower intramolecular change. The order of magnitude of the kinetic constants is suggestive of a major structural change induced by the binding of the dipeptide to the zymogen. Materials and methodsThe p-guanidinobenzoate-derivative of trypsinogen was prepared according to Kerr et al. [3] _ Crystalline
Sb'I~IARYPolyelectrolyte field effects are indicated by paxticularly large variations of thermodynamic and kinetic constants with ionic strength. Some fundamental principles of local electric field effects in the microenviz-onmen~; of polyelectrolyte struetura~ are discussed, aiming at a reliable analysis of shifts in equilibrium and rate constants of ionic reaction partners with ionic strength. It is shown that the analytical expressions, within certain limitations, are suitable to determine effective charges involved in polyionic field effects on ionic reactions in the immediate neighhorhood of a polyelectrolyte structure. An instructive example for such an observation is the neuro~nzyme acetylcholinesterase. The results of a relaxation--kinetic titration of this anionic enzyme (which hydrolyzes the cationic neuro-activator acetylcholine) with a cationic ligand suggest that the micro environment of the enzymeactive site consists of at least six anionic groups. A large effective, negative charge number is also reflected in the comparatively large association rate coefficients.These results suggest that an enzyme surface area considerably larger than the ligand binding site itself is effective in trapping a cationic ligand. This larger surface area may include peripheral anionic sites from which iigand would move to the active site by surface diffusion.
Clinical Pharmacology & Therapeutics (1996) 59, 208–208; doi:
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