Trapping succinimides in aged polypeptides by chemical reduction

Abstract

Cyclization of aspartic acid and asparagine to succinimides is thought to be a common spontaneous aging reaction in proteins, but the instability of the succinimide ring has made it difficult to directly measure this structure. Chemical reduction has now been tested as a means of trapping succinimides as stable derivatives, homoserine and isohomoserine. Two succinimide-containing compounds were tested in this manner. First, polysuccinimide was reduced by sodium borohydride to a derivative that contained homoserine and isohomoserine in amounts that were consistent with the content of succinimide determined independently by quantitative hydrolysis. The identity of isohomoserine was confirmed by its resistance to degradation by L-amino acid oxidase, and through its synthesis by an alternate route involving borane reduction of asparagine. Second, in a test of this approach on a peptide mixture with only a trace-content of succinimide, isohomoserine and homoserine were formed as reduction products in amounts equivalent to the trace content of succinimide in the mixture. Detection of the products of the chemical reduction of polypeptides is therefore diagnostic of succinimides, and can be successfully applied at the trace sensitivity necessary for studies of naturally aging proteins. A related study of the reduction of aspartyl and beta-aspartyl residues to, respectively, homoserine and isohomoserine, is described in the accompanying manuscript (Carter and McFadden, 1994).

Retracted: Nanobubbles influence on BSA adsorption on mica surface

“…Thus, it is easily identified if the BSA film is affected by the nanobubbles. More importantly, as the most abundant protein found in blood and serum, 33 albumin has become a model biomolecule in studies on protein adsorption. 31,34,35 The adsorption behavior of BSA on varied surfaces have been reported.…”

Determination of Β-isomerized aspartic acid as the corresponding alcohol

“…A mixture (20: 80) of tetragastrin and isotetragastrin (L-Trp-LMet-/~-L-Asp-L-Phe-NH2) was prepared by treating tetragastrin methyl ester at pH 9.5 for 22 hr at 25~ (McFadden and Clarke, 1986a; see also the accompanying manuscript). Safety precautions for handling borane, and the synthesis of standard isohomoserine are described in the accompanying manuscript (Carter and McFadden, 1994).…”

“…Conditions of cation-exchange chromatography and ninhydrin detection of amino acids were as described (Carter and McFadden, 1994). As described therein, the ninhydrin color-yield for aspartic acid and homoserine are essentially equal.…”

“…The numbered peaks are described further in Table I. Table I in accompanying manuscript (Carter and McFadden, 1994). i, Elution times varied by up to +0.3 min in duplicate analyses.…”

Study on the interaction between anti‐tuberculosis drug ethambutol and bovine serum albumin: multispectroscopic and cyclic voltammetric approaches

“…It is reported that digitoxin binding is independent of sites I and II and binds to site III. [33] According to Carter and co-workers, sites I and II appear to be located in the hydrophobic cavities of subdomains IIA and IIIA of serum albumin, respectively [34] The evidence for this proposal was that only warfarin region drugs were affected by chemical modification of the lone tryptophan residue of serum albumin. In order to establish the binding site in BSA for EMB, competitive binding studies were performed using site probes like warfarin, ibuprofen and digitoxin.…”