Cooperation of enzymes responsible for polymerisation and methylation in pectin biosynthesis.

Some more properties of a particulate enzyme preparation from mung bean shoots capable of the formation of polygalacturonate as well as its methyl ester are reported. 1. When the preparation was freed of traces of endogenous nucleotide uronic acids by digestion with phosphodiesterase or by preincubation up to 2 hours, the methylation was still possible. This sustains the recently made proposal that the methylation proceeds by transmethylation directly to polygalacturonate and not intermediary to nucleotide uronic acids. 2. The formation of the polygalacturonate chains from radioactive UDP-galacturonate is indepen­ dent of the methylation process. 3. The polygalacturonate methyl transferase does not methylate exogenous polygalacturonate. In contrast, the rate of pectin methyl ester formation is strongly increased if additional polygalac­ turonate is pregenerated in the enzyme preparation by incubation with UDP-galacturonate followed by digestion with phosphodiesterase. This may indicate that the enzymes for polymerization and methylation as well as the pectic substances are localized intimately together in structural com­ partments.