sentence: The genes encoding the regulatory ( GCLM ) and catalytic ( GCLC ) subunits of γ - glutamylcysteinyl ligase , a rate-limiting enzyme for glutathione synthesis , are well known targets of Nrf2 ( Moinova and Mulcahy , 1999 ; Solis et al ., 2002 ; Bea et al ., 2003 ; Sekhar et al ., 2003 ) .