Immunological detection and quantification of oxidized proteins by labelling with digoxigenin.

An immunological assay, based on the digoxigenin/anti-digoxigenin system, was developed to detect and quantify carbonyl moieties that result from oxidative damage to proteins. Bovine serum albumin (BSA) was oxidized by a hydroxyl radical-generating system consisting of ascorbate/Fe(III)/O2. The resulting albumin-derived carbonyls were labelled with digoxigenin-hydrazide and detected by dot blotting with an anti-digoxigenin antibody conjugated to alkaline phosphatase. Quantification was carried out by a densitometric analysis. This system allows the detection of a pmole-amount of carbonyl groups on blots. The assay covers a range of sensitivity from 1.26 to 126 pmoles. Another feature of this method is its application to a complex protein mixture (homogenate) to analyze the oxidative status of individual proteins, as are shown for intestinal brush border membrane homogenate of a rat.

Synthesis of the pro-peptide of subtilisin BPN'.

Subtilisin, a bacterial serine protease, is secreted as pre-pro-subtilisin. Previously, we demonstrated that the pro-peptide moiety of intact pro-subtilisin can guide the folding of inactive protein to active enzyme both in an intramolecular (6) and intermolecular manner (18). Herein is reported the total chemical synthesis of the pro-sequence (77 amino acids) of pre-pro-subtilisin BPN' carried out by solid phase methods. The structure was confirmed by both sequencing and amino acid analysis of the fragment peptides resulting from a V-8 protease digest. Preliminary studies indicate that the synthetic pro-peptide itself can renature denatured subtilisin BPN'. This study demonstrates a novel method for examining protein folding with the aid of exogenously added synthetic peptides.