°13C shift referred to TMS.respectively.33 The effect of self-association is probably negligible, since the concentration of the solute is low (1 mol %) in polar solvents. Then it is found that the 14N shifts of imidazole in acetone and DMSO (proton acceptors) are shifted downfield with respect to methanol, water, and trifluoroacetic acid (proton donors). The difference of 14N shifts is 6-9 ppm over the range of the experimental error.Similarly upfield 14N shifts of 6 ± 3 ppm and 7.4 ± 3-9.8 ± 5 ppm are observed in pyrazole and 1,2,4-triazole, respectively. These values are recognized as about half of the corresponding values for A-methyl derivatives, taking into account the argument described above.Sometimes difficulty arises in observing 14N shifts in protonated species, because a longer correlation time due to protonation tends to broaden nmr lines and make the two-and three-bond N-H couplings unobservable. Protonation shifts on imidazole and thiazole are obtained by the decoupling of one-bond N-H couplings. The upfield 14N shifts are 41 ± 3 ppm and 123.1 ± 3 (34) H.

No abstract

The binding of concanavqlin A to T but not B mouse spleen lymphocytes increases Ca-2+ uptake in these cells which is measurable by 45 s and complete by 1 min. Dibutyrl cyclic AMP, but not sodium azide inhibits induced Ca-2+ uptake, wheras dibutyryl cyclic GMP enhances it. B cell mitogens do not cause a similar Ca-2+ uptake in mouse B lymphocytes. The induction of increased Ca-2+ uptake by T cells is discussed in terms of gated membrane channels for Ca-2+.

Since decompression from depth is known to produce a fall in platelet count, the effect of altitude decompression and high-altitude exposure on platelets was investigated. Sixteen subjects decompressed without hypoxia to 20,000 ft simulated altitude for two hours showed a significant (P less than 0.01) drop in circulating platelet count of approximately 10% for three days following decompression. Four of five subjects similarly exposed had a shortened autologous platelet survival compared to that prior to exposure. Subjects exposed to 9,800 ft and then 17,600 ft in a mountain environment showed a significant mean decrease in platelet count on day 2 of 7% and 25% respectively, which had returned to control by day 5. Nonhypoxic and hypoxic decompressed rabbits which received homologous chromium-51-labeled platelets had an increase in lung radioactivity compared with sea-level controls. It is postulated that altitude decompression produces platelet reductions similar to these seen after decompression from depth, and that platelets sequester in the pulmonary vascular bed.

and antibodies directed against p-azobenzenephosphonate was shown not to be due to any possible conformational changes caused by modification of amino groups outside of the antibody combining sites since loss of sites could be prevented completely by the presence of hapten during maleylation, and since the modification of all the amino groups in antibodies prepared against a neutral hapten (3-azopyridine) and against a positively charged hapten (p-azophenyltrimethylammonium) resulted in no change in either their number of antibody combining sites or their average binding constants. These results establish the presence of two kinds of chemically different combining sites in antibodies against negatively charged haptens, those containing an amino group and those that do not. In addition they establish the absence of amino groups in the combining sites of antibodies prepared against a positively charged and a neutral hapten.for amino groups. Maleic anhydride modifies essentially all of the amino groups present in protein molecules, and can be easily removed by acid hydrolysis.This report describes the effect on antibody combining sites following chemical modification of all of the free amino groups in antibody molecules by maleic anhydride under mild conditions. The results demonstrate the direct involvement, in varying amounts, of amino groups in the combining sites of antibodies prepared against certain negatively charged haptens (p-azobenzenearsonate, p-azobenzenephosphonate, and p-azobenzoate), and the absence of amino groups in the combining sites of antibodies prepared against a positively charged (p-azophenyltrimethylammonium) and a neutral (3-azopyridine) hapten. Materials and MethodsBuffers. The buffers used in this study included: Tris buffer (pH 8.0) (0.1 m Tris-HCl, 0.002 m EDTA), Tris-NaCl buffer (pH 8.0) (0.02 m Tris-HCl, 0.15 m NaCl, 0.002 m EDTA), and borate buffer (pH 9.0) 1941

No abstract

Natural abundance high-resolution carbon-13 Fourier transform nuclear magnetic resonance (W NMR) studies a t 25 MHz have been carried out on selected amino acids, linear peptides and proteins, The pH dependence of the 13C resonances has been studied in detail in several cases. For L-histidine, the 18C chemical shifts of all six carbon atoms are sensitive to the ionization state of the titrating carboxyl, imidazole and amino groups. The data for each carbon resonance have been computer-fitted to a sum of three theoretical curves based on a simple proton-association equilibrium for each transition. The extent of chemical shift change upon ionization of a nearby group has been interpreted in terms of two competing effects, inductive (through-bond) and electric field (through-space) effects.NMR spectra of the amino-terminal 1-13, 1-15, and 1-20 peptides of bovine pancreatic ribonuclease A have been analyzed. Detailed resonance assignments have been made based on comparisons with the results for the free amino acids, shift effects for amino acids in small peptides, internal peptide bond effects and differences in amino acid composition. There is considerable correspondence between the observed 13C chemical shifts of these peptides and those predicted from the shifts of the component amino acids.Proteins of varying molecular weight have been studied to evaluate the potential of 1% NMR investigations of structure and conformation. A comparison has been made between the 18C NMR spectra of hen egg-white lysozyme in its native and reduced states. The spectrum of the fully reduced species appears to be well represented by the sum of the spectra of the individual amino acids, both in chemical shift and line width, whereas that for the native form exhibits consistently broader resonances. Similar results were obtained for ribonuclease A. At the current level of resolution, it is impossible to discern whether this line broadening derives from shorter relaxation hime effects due to restricted motion, chemical shift non-equivalence between the same chemical groups, or both. However, it does appear that there are separately resolved peaks corresponding to CB-carbons for different threonyl residues, as well as for the C-4 ring carbons of the several tyrosyl residues in native hen egg-white lysozyme. Spectra of carbonic anhydrases (Mr 4 30000), which lack disulphide bonds, showed somewhat poorer resolution than the smaller proteins. TheIn recent years, there has been considerable interest in the potential use of nuclear magnetic resonance (NMR), particularly proton magnetic resonance (lH NMR), for characterizing protein conformation and interactions [l -31. In principle, lH NMR spectra of proteins contain a wealth of

pH dependent "C chemical shifts for phenylglycine, phenylalanine, and phenylalanyl derivatives demonstrate that the electronic distribution of the phenyl group depends upon the distance of charged groups from the phenyl ring. The pattern of chemical shifts and the results of CND0/2 MO calculations indicate that this is due to polarization of the phenyl n electron system. I1C chemical shifts and CND0/2 calculations for a-and P-substituted phenylalkanes (substituent = NH3+, C1 or Br) provide further evidence for a n polarization effect.Les deplacements chimiques en "C relies au pH de la phenylglycine, de la phenylalanine, et des derives de la phtnylalanine, ont demontre que la distribution electronique du groupe phinyle est fonction de la distance entre les groupes charges et I'anneau phenyle. L'arrangement des deplacements chimiques ainsi que les resultats obtenus par des calculs CND0/2 MO montrent que cette relation est causie par la polarisation du systkme d'electrons n du phtnyle. Les deplacements chimiques en "C et les calculs CND0/2 pour des phenylalcanes cu et P substitues (substituant = NH3+, CI, ou Br) montrent des caracteristiques jouant en faveur de cet effet de polarisation n.