protein-extracted lucerne fiber was used as carbon and energy source for production of extracellular polygalacturonate lyase by thermomonospora curvata. the optimal fiber concentration was 1.5 (w/v); peak lyase activity in culture fluid occurred after 3 days growth at 53 $degree$ c. during that time, lyase biosynthesis was controlled through induction; production was accelerated by adding small amounts of pectin or by grinding the fiber to 40-mesh particle size to release more inducer. after 3 days growth, lyase activity decreased; inactivation of the enzyme was delayed by the presence of 1 mm ca or by inhibition of serine proteases with 0.05 mm phenylmethylsulfonly fluoride. the molecular weight of the lyase produced during growth on the fiber was 35 kda compared to 56 kda for the enzyme produced on pure pectin. the k//m of the 35-kda form was 0.54 pectin compared to 0.06 for the 56-kda form. the smaller form was rapidly inactivated at 60 $degree$ c, the optimal temperature for activity of the larger form. (author abstract) 30 refs