The Action of Sulphuric Acid on Gliadin: With Special Reference to the N-Peptidyl→o-Peptidyl Bond Rearrangement

Abstract

Treatment of gliadin with sulphuric acid transposes peptide bonds of serine from the amino t o the hydroxyl group. Maximum transposition, 60-70% of the theoretica1, occurs when the protein is treated with anhydrous sulphuric acid a t 0°C. for 35 hr. No rearrangement was detected a t threonine residues. Examination of the peptide materiaI, obtained from the rearranged protein by Elliott's degradation method, indicates apparent "hon~ogeneity". In an alternative scheme for the degradation, nitrous acid deamination of free amino groups was used. The resulting loss in serine content of the protein is direct evidence for the acyl migration of peptide bonds. Incorporation of sulphur and partial disappearance of several amino acids accompany the sulphuric acid treatment. The occurrence of these secondary reactions imposes limitations on the use of sulphuric acid as a reagent for the specific fission of peptide bonds. INTRODUCTIONAttention has recently been directed towards methods which effect fragmentation of protein molecules in a predictable manner. Especially significant is Elliott's procedure for the cleavage of peptide bonds (7, 8, 9) a t the amino groups of the P-hydroxyamino acids, serine and threonine. I t is based on the strong acid-induced N-acyl+O-acyl transformations studied earlier by Bergmann, Brand, and Weinmann (2), Desnuelle and Casal ( 5 ) , and Desnuelle and Bonjour (G), and is briefly outlined in the equations below:. . This N-acyl+O-acyl migration might also occur ~vllere the €-amino groups of f hydroxylysine (26) are linlied in a peptide bond.The treatment of silk fibroin with 97.5% sulphuric acid for three days a t 20°C. (8) caused rearrangelllent in only 66% of the serine residues, the major N-terminal residue detected by the dinitrolluorobenzene method (24) being serine. The non-reactivity of the other serine residues was thought t o result 1AIanuscript received M a y 26, 1955.

Stability of 20 Biogenic Amino Acids in Concentrated Sulfuric Acid: Implications for the Habitability of Venus' Clouds

“…Only one of the chemically modified amino acids is highly reactive in concentrated sulfuric acid. Tryptophan undergoes rapid and complex reactivity that likely involves the formation of highly diverse cross-linked species * as, for example, noted in passing by Ramachandran and McConnell ( 1955 ). We note that in water tryptophan can readily be oxidized by reactive oxygen species such as singlet oxygen that can be generated from atmospheric oxygen by UV light or reaction with metals, such as iron, to react with a variety of species (Simat and Steinhart, 1998 ; Bellmaine et al ., 2020 ).…”