Tissue distribution of acetyl-CoA carboxylase in leaves of leek (Allium porrum L.)

The distribution of acetyl-CoA carboxylase between the epidermal and mesophyll layers of leek leaves was determined. The specific activity of acetyl-CoA carboxylase was approximately three-fold higher in extracts of the epidermis than in those from the mesophyll layer. Four prominent biotinylated polypeptides of approximate molecular masses 240, 85, 37, and 35 ku (kDa) were detected in leaf extracts. The biotin-containing subunit of the homomeric acetyl-CoA carboxylase, the 240-ku biotinylated polypeptide, accumulates exclusively in the epidermis of leek leaves. Three of the subunits of the heteromeric acetyl-CoA carboxylase (the biotin carboxyl carrier, the biotin carboxylase, and beta-subunit of the carboxyltransferase) were equally abundant in leek mesophyll and epidermal tissues. These data indicate that leek leaves contain two structurally distinct isozymes of acetyl-CoA carboxylase, one of which, the homomeric form, is restricted to the epidermis.