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E Breslow

Publications and source records attributed to E Breslow.

8 recordsLinked to original sources
PubMed1979

Fluorescence studies of native and modified neurophysins. Effects of peptides and pH.

The effect of neurophysin-hormone interaction on the environment of the single tyrosine of bovine neurophysin (Tyr-49) and on that of the tyrosine of oxytocin and vasopressin was studied by fluorescence; tyrosine-free peptides were used to determine effects on Tyr-49, and acetylated neurophysin was used to determine effects on the hormone tyrosine. Binding increases the fluorescence intensity of Tyr-49 by 130% while the fluorescence of the hormone tyrosine is almost completely quenched. Correlation of these results with those obtained on binding oxytocin or vasopressin to native neurophysin indicates that in the hormone complexes less than half of the fluorescence of Tyr-49 is lost by Förster energy transfer to the quenched hormone tyrosine. These results support spin-label studies in indicating that the distance between Tyr-49 and the tyrosine of hormone bound to the strong hormone binding site is greater than 5 A. In the absence of peptides, the fluorescence of Tyr-49 increases by 40% on lowering the pH from 6.2 to 2. Titration of the acid fluorescence transition in bovine neurophysins-I and -II, and in bovine neurophysin-II treated with carboxypeptidase B to remove the Arg-Arg-Val sequence at the carboxyl terminus, indicates that this transition is due to titration of a side-chain carboxyl with an intrinsic pK of 4.6. The effects of guanidine, glycerol, and disulfide cleavage on the magnitude of the acid transition indicate that the conformational information necessary for the transition resides within the amino acid sequence adjacent to Tyr-49. Accordingly, the fluorescence acid transition is attributed to decreased quenching by Glu-46 or Glu-47 upon protonation. Glycerol is shown to perturb the glutamate-tyrosine interaction in the absence of general conformational effects. Comparison of the fluorescence low-pH transition with that of the low-pH circular dichroism transition of nitrated neurophysins suggests that the fluorescence and CD transitions reflect related, but not necessarily identical, phenomena. In an appendix, evidence is presented which suggests that the products of carboxy-peptidase digestion of bovine neurophysin-II are the same as two minor bovine neurophysin components, one of which is neurophysin-C.

Animals↗
PubMed1979

Identification and observation of alkyl proton resonances of the amino-terminal residues of bovine neurophysins. Evidence for conformational differences between neurophysin-I and neurophysin-II.

Analysis of the 220 MHz proton magnetic resonance spectra of bovine neurophysins-I and -II and of the effects of pH and succinylation of these spectra has allowed identification of the -CH3 proton resonances of the amino-terminal alanine of both proteins and of the -CH3 resonances of methionine-2 of neurophysin-II. The alanine -CH3 resonance of neurophysin-I is a sharp doublet at all pH values between 1 and 10.5 indicating relatively few restrictions on its mobility. By contrast, the -CH3 resonances of the amino-terminal alanine and methionine-2 of neurophysin-II undergo pH-dependent changes in broadening compatible with the formation of an intramolecular salt-bridge at neutral pH between the protonated alpha-amino and an unprotonated side chain carboxyl. The results suggest that differeces in the properties of the two proteins are partially mediated by conformational differences involving their amino-terminal sequences. The potential usefulness of the amino-terminal resonances as n.m.r. 'reporter' signals is additionally demonstrated by studies of the effects of spin labels on the neurophysin-I amino-terminal alanine resonance; these studies place the amino-terminus of neurophysin-I approximately 14 A from residue 3 of peptides bound to the strong neurophysin hormone-binding site.

Amino Acids↗
PubMed1976

Hydrogen ion interactions of horse spleen ferritin and apoferritin.

The interactions of horse spleen ferritin and its derivative apoferritin with H+ ions were studied by potentiometric and spectrophotometric titration; to aid in data analysis, heats of ionization over a limited pH range and amide content were also determined. Per apoferritin subunit, all tyrosine and cysteine side chains, two of the nine lysine side chains and at least three of the six histidine side chains were found not to titrate; a preliminary but self-consistent analysis of the titration data is proposed. The titration curve of ferritin was identical with that of apoferritin in the pH range 5.5 to 3. In addition, under the conditions used, the reactivities of ferritin histidines to bromoacetate and of ferritin lysines to formaldehyde were identical with those in apoferritin. Above pH 8, a time-dependent titration of the ferritin core occurs which prevents comparison of the titration curves of the two proteins in this region. However, in the pH regions 5.5 to 7.5, two extra groups per subunit titrate reversibly in ferritin relative to apoferritin. Moreover, although the isoionic points of ferritin and apoferritin are identical in water, the isoionic point of ferritin is 0.5 pH unit lower than that of apoferritin in 0.16 to 1 M KCl. The different effects of KCl and NaCl on the two proteins indicate the presence of cation binding sites in ferritin that are absent in apoferritin and possibly also the presence of anion binding sites in apoferritin that are occupied in ferritin by anions of the core. The difference between the isoionic points of the two proteins in KCl has been interpreted to indicate the presence of approximately 2 phosphate residues per ferritin subunit which serve as cation binding sites and which are negatively charged at the isoionic point in KCl. These phosphates may also represent the additional residues that titrate in ferritin between pH 5.5 and 7.5, or may interact with positively charged residues on the inner surface of the ferritin shell, or both.

Animals↗