I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

THE structure of proteins is probably the most Jvumpapant and possibly the most difficult of the maflpr uifeolved problems of chemistry, at least for the immediate future, and coming at a time when preparations are being made in numerous places to storm this citadel, the present volume is very timely since it gives clear reviews of many of the new methods which will be employed. It reflects the present trend of protein research towards exact analysis and what one might call the ‘classical’ organic approach to the problem. The X-ray method has clear possibilities, but they are more limited and at the same time involve greater difficulties than was originally expected. In his excellent survey of this field, I. Fankuchen sums up the position with regard to crystalline proteins as follows. “Single protein crystals can be made to yield exceedingly detailed X-ray diagrams and yet one must admit that to date the results of such single crystal studies have been disappointing; disappointing because very beautiful and complete data have so far only yielded comparatively meagre results”—a conclusion which broadly coincides with the views expressed in the discussion at the Roentgen celebration in London. It appears that although we can expect definite information about the number and arrangement of protein molecules in the unit cell, a complete structure analysis lies in the distant future; perhaps not a surprising situation when one contemplates the empirical formula recently given by Brand and his co-workers for lactoglobulin, one of the few cases in which the analyses approach finality, namely, C1864 H3012 N468 S21 O576, or particularizing the amino-324 acids by easily recognisable abbreviations, as follows: Gly8 Ala29 Val21 Leu50 Ileu27 Pro15 Phe9 CySH4 (CyS)8 Met9 Try4 Arg7 His4 Lys33 Asp36 Glu24 (Glu-NH2)32 Ser20 Thr21 Tyr9 H2O4! It might perhaps not unfairly be said that the chief contribution of the X-ray studies has been to demand and stimulate more accurate analyses. Advances in Protein Chemistry Edited by M. L. Anson John T. Edsall. Vol. 2. Pp. xiii + 443. (New York: Academic Press, Inc., 1945.) 6.50 dollars

Advances in Protein Chemistry

Publisher Summary This chapter classifies the models concerning the different aspects of ribosomal translocation and discusses them in the light of today's factual grounds. It briefly reviews the two-tRNA-binding-sites (A and P) model for the ribosomal elongation cycle. Intermediate and additional tRNA binding positions may exist without detriment to the main scheme. A three-tRNA-binding-site model where the sequence of events differs from the two-tRNA-binding-sites (A and P) model is also mentioned in the chapter. The energetics models of ribosomal translocation are classified into two groups. One group includes the models where ribosomal ligands, in particular tRNAs, are actively pushed or pulled, mechanically or electrostatically, from one position to another at the expense of the energy of coupled GTP hydrolysis (GTP-driven translocation). The other group of models implies that the translocational displacements are thermodynamically spontaneous and proceed as ribosome-channeled diffusional movements of the ligands, the role of EF-G being considered as an entropic catalyst and GTP as a cleavable effector of EF-G (EF-G-catalyzed translocation). The preference is given to the second group of models. The kinematic and topographical models of ribosomal translocation are also discussed in the chapter.

Ribosomal Translocation: Facts and Models

The binding affinities of tRNAPhe, Phe-tRNAPhe, and N-AcPhe-tRNAPhe from either Escherichia coli or yeast to the P, A, and E sites of E. coli 70S ribosomes were determined at various ionic conditions. For the titrations, both equilibrium (fluorescence) and nonequilibrium (filtration) techniques were used. Site-specific rather than stoichiometric binding constants were determined by taking advantage of the varying affinities, stabilities, and specificities of the three binding sites. The P site of poly(U)-programmed ribosomes binds tRNAPhe and N-AcPhe-tRNAPhe with binding constants in the range of 10(8) M-1 and 5 X 10(9) M-1, respectively. Binding to the A site is 10-200 times weaker, depending on the Mg2+ concentration. Phe-tRNAPhe binds to the A site with a similar affinity. Coupling A site binding of Phe-tRNAPhe to GTP hydrolysis, by the addition of elongation factor Tu and GTP, leads to an apparent increase of the equilibrium constant by at least a factor of 10(4). Upon omission of poly(U), the affinity of the P site is lowered by 2-4 orders of magnitude, depending on the ionic conditions, while A site binding is not detectable anymore. The affinity of the E site, which specifically binds deacylated tRNAPhe, is comparable to that of the A site. In contrast to P and A sites, binding to the E site is labile and insensitive to changes of the ionic strength. Omission of the mRNA lowers the affinity at most by a factor of 4, suggesting that there is no efficient codon-anticodon interaction in the E site. On the basis of the equilibrium constants, the displacement step of translocation, to be exergonic, requires that the tRNA leaving the P site is bound to the E site. Under in vivo conditions, the functional role of transient binding of the leaving tRNA to the E site, or a related site, most likely is to enhance the rate of translocation.

Affinities of tRNA binding sites of ribosomes from Escherichia coli

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2883%2981122-3

Quantitative study of interaction of deacylated tRNA with Escherichia coli ribosomes: Role of 50 S subunits in formation of the E site

The interaction of N--Acetyl--Phe--tRNA Phe with 70 S ribosomes is a reversible process in the absence as well as in the presence of messenger. The equilibrium binding constants of these interactions were measured at different magnesium concentrations and temperatures and thermodynamical quantities computed. The enthalpy of the formation of complexes with the P site of ribosomes is larger by 6,000 cal/mol in the presence of poly (U) than in the presence of poly (C) or in total absence of messenger. Free energy differences are rather small, the association constants differ less than one order of magnitude. The association constant of N--Acetyl--Phe--tRNA Phe with the A site of ribosomes is 30--50 times lower than with the P site even in the presence of poly (U).

Interaction of N-acetyl-phenylalanyl-tRNAPhe with 70S ribosomes of Escherichia coli

The mechanism of codon-anticodon interaction in ribosomes. Heterogeneity of tRNA complexes with 70-S ribosomes of Escherichia coli.

A modulation free Electron Spin Resonance spectrometer was used for the registration of spectral absorption lines of a spin-labeled Escherichia coli phenylalanine tRNA in solution with low (less than 0.1%) line shape distortion. The analysis of line shape of two different spin-labels introduced into position 8 revealed that phenylalanine tRNA in solution exists as a mixture of two conformers, the equilibria between conformers being dependent on pH, concentration of magnesium and functional state of tRNA (deacylated, aminoacylated or peptidylated). There are no overall structural rearrangements upon aminoacylation or peptidylation of tRNA. The observed small changes of spectral line shape can be assigned to shifts in conformational equilibria.

Study on conformational states of Escherichia coli tRNAPhe in solution by a modulation-free ESR-spectrometer.

Earlier the existence of two conformers of Phe-tRNAPhe of E. coli was demonstrated because one of them yields complexes with 70S-poly(U) of extremely high affinity and the other with at least a 105 lower binding constant. We denote the first conformer as HAC (high affinity conformer) and the second as LAC (low affinity conformer). This high difference in binding constants was used for studying the process of reversible interconversion of conformers of Phe-tRNAPhe. The transition kinetics of LAC to HAC in conditions when the latter is stable (in the presence of magnesium ions) was studied and a high value of activation energy (35 kcal/mole) found. The interconversion is the first order reaction and equilibrium does not depend of overall Phe-tRNA concentration.

Vladimir B. Odinzov

Papers

Interaction of N-acetyl-phenylalanyl-tRNAPhe with 70S ribosomes of Escherichia coli

The mechanism of codon-anticodon interaction in ribosomes. Heterogeneity of tRNA complexes with 70-S ribosomes of Escherichia coli.

Study on conformational states of Escherichia coli tRNAPhe in solution by a modulation-free ESR-spectrometer.

The interconversion of conformers of phenylalanyl-tRNA with different affinity to 70S ribosomes of Escherichia coli