The properties of the extra-cellular enzyme, α-l-arabinofuranosidase, produced by Phytophthora palrmivora was studied in some detail. The optimum pH for the enzyme activity was 4.0, a level which is typical of the host plant tissues. Activity was stable over a considerable range of pH (2.0–8.0) depending on the length of time of e.Kposure to this condition. The optimum temperature was 50° C, higher than that recorded for its production. The activity was thermostable between 10 and 50° C; thermal inactivation was recorded at 70° C. The data from the Q10 values indicated that thermal inactivation beyond 60° C might be due to the denaturation of the enzyme protein.
The molecular weight determination indicated that the enzyme existed in two major molecular units of 63, 100 and 15, 850, respectively.
The enzyme activity was proportional to the log enzyme concentration. The enzyme was highly specific for its substrate; the average Km value was 0.65 mM. The activity was inhibited by arabinogalactan competitively, the Ki value being 5.83 mM. The activity was enhanced by the presence of calcium arabonate tetrahydrate. The activation was due to Ca2+. Plant metabolic analogues affected enzyme activity; L-arabinose was the most inhibitory sugar, and L-glutamine the most inhibitory amino acid. Oxidized phenolics were more potent than the unoxidized forms.
The possible role of the enzyme in plant pathogenesis was discussed.