N,N'-BISFORMYL DITYROSINE IS AN IN-VIVO PRECURSOR OF THE YEAST ASCOSPORE WALL

The amino acid, dityrosine, is a major component of the spore wall sur face of the yeast Saccharomyces cerevisiae, where it is part of a high ly cross-linked macromolecular network of yet unknown chemical structu re, consisting mostly of glucosamine, dityrosine and few other amino a cids, Biosynthesis of the dityrosine moiety of this network consists o f several steps, including the chemical modification of free L-tyrosin e and the subsequent oxidative cross-linking of the modified tyrosine residues (catalyzed by a cytochrome P-450), leading to soluble dityros ine-containing spore wall precursors. We isolated, purified and charac terized the dityrosine-containing precursor that appears late in spore wall synthesis and that is thought to be directly incorporated into t he maturing spore wall. Chemical and spectroscopic analyses showed tha t this precursor is N,N'-bisformyl dityrosine. In addition, we identif ied a tyrosine-containing spore wall precursor as N-formyl tyrosine. T he elucidation of the chemical structure of soluble spore wall precurs ors is crucial for the characterization of the function of the enzymes involved in maturation of the spore surface, e.g. by in vitro systems . A dityrosine-containing fragment, which was solubilized from mature spore walls by partial hydrolysis, was identified as N-formyl dityrosi ne. Mature spore walls contain significant amounts of N-formyl dityros ine and N,N'-bisformyl dityrosine. This supports the assumption that t he dityrosine-containing macromolecular network on the spore surface h as an unusual, nonpeptidic structure.