[Differentiation of polygalacturonase preparations]

[Effects of molecular parameters of galacturonan substrate on the activity of a polygalacturonase from tomatoes]

The activity of a major form of the tomato polygalacturonase (EC 3.2.1.15) depends of the origin of the galacturonan substrates (apple, citrus) as well as upon the molecular mass, the degree of esterification and the distribution of the ester methoxyl groups. Optimal substrates are citrus pectic acids with a degree of esterification < 1% and a molecular mass corresponding to a viscosity number [eta] = 90 ml/g galacturonan. In the [eta] range from 16 to 474 ml/g, the Km values decrease to constant amount of 15.6 mM galacturonic acid units, which corresponds to 0.27% galacturonan. In a statistical distribution of the ester methoxyl groups, the activity reaches zero in the range of the degree of esterification from 80 to 90%. Enzymatically de-esterified pectins with a degree of esterification < 32% and a block-like distribution of the ester methoxyl groups behave as comparable pectic acids. In summary, there is a good agreement between these enzymesubstrate interactions and those of endopolygalacturonases from Aspergillus spec. Differentiations manifested themselves only in the transition range between macromolecular galacturonan substrates and oligomeric substrates below the established critical molecular mass.

[Mode of action and inhibition of polygalacturonase covalently bound to polysaccharide and glass carriers]

Endo-polygalacturonase (EC 3.2.1.15.) from Aspergillus spec. is much changed as far as its mode of action and the interaction with vegetable inhibitors of pectinase (from green beans and cucumbers) are concerned when it is covalently bound to insoluble carriers (Sepharose, cellulose powder, macroporous glass and nonporous ballotinis). Whereas a 2% degradation of substrate by the soluble enzyme caused a 50% decrease of viscosity of citrus pectic acid, the comparable degradation of substrate was increased to a level of about 10% with the investigated polygalacturonase carrier complexes apparently independent of the properties of the carriers and the kind of binding of the enzyme. In contrast to this the higher degradation of substrate of 15 and 20% respectively which was further stated at a 50% decrease of viscosity is unambiguously connected with the carriers and is in direct correlation with the specific activity of the polygalacturonase carrier complexes. Contrary to the soluble enzyme the covalently bound enzyme produces more lower oligomerous galacturonic acids by an exo-mechanism or by multiple attack already at the beginning of the hydrolysis of pectic acid. During the final stage there is an enrichment of trigalacturonic acid besides mono- and digalacturonic acids independent of the state of solution of the enzyme. It could further be stated that the strong inhibition of the soluble endo-polygalacturonase by selected pectinase inhibitors which was described earlier is reduced by degrees with the enzyme covalently bound to the insoluble carriers.