Abstract
Casella procedures using dilute neutral permanganate solutions for 5-15 min produce a homogeneous staining of human elastica more suggestive of protein than of carbohydrate determinants. Observed blockage of this reaction by preoxidative acetylation or dinitrophenylation, but not by bromination or nitrosation, indicates tyrosine residues as likely determinants, as does the resemblance of the Casella staining pattern to that yielded by diazotization coupling procedures. By analogy with the known lability of free phenol to dilute neutral permanganate, it is postulated that the alkylphenolic tyrosine residue would thereby be oxidized to alkylcarboxylic acid via an alkylaldehyde intermediate stage. Hence it is significant that prolongation of permanganate treatment leads to progressive diminution of Schiff reactivity with concurrent development of increasing basophilia of carboxylic acid type. In confirmation, the precipitated floccules of a synthetic polytyrosyl peptide (mol wt 60,000) embedded in gelatin were found to give negative direct and periodic acid-Schiff reactions, but a strongly positive Casella reaction and marked permanganate-induced basophilia.