Lidamycin with high antitumor activity is a novel enediyne antitumor antibiotic producedby Streptomyces globisporus C1027. The 75 kb biosynthesis gene cluster of lidamycin containing 33 open reading frames has been cloned from S. globisporus C1027. In this paper,the function ofsgcD (ORF24) is investigated. Gene disruption experiment proved that sgcD is involved in lidamy-cin biosynthesis. With homologous comparing analysis, we deduce that sgcD codes aminomutasecatalyzing α-tyrosine to β-tyrosine which is one motif for lidamycin. To identify the function of en-zyme coded by sgcD, sgcD is cloned into vector pET30a for inducing expression and the activity ofexpression product is analyzed. The result showed that the expression product ofsgcD has theactivity of aminomutase. Aminomutase coded by sgcD is the first characterized enzyme involved inthe biosynthesis of enediyne antitumor antibiotics. Our research will be helpfulto clarifying thebiosynthesis mechanism of such kind of antibiotic and to producing new antitumorcompounds.