Characterization of linamarase of latex and its localization in petioles in cassava.

The distribution of linamarase in latex and its purification, characterization, and immunocytochemical localization in petioles were studied in order to get an insight into the process of cyanogenesis in cassava. Crude latex exudate exhibited low linamarase activity, but on dilution the activity increased about fivefold. Assay using petiole latex collected in isotonic medium showed that the enzyme was distributed in vesicle-like structures. In vitro studies showed that about 50% activity was released from the vesicle into the medium within an hour. Latex linamarase was purified by ammonium sulfate fractionation and DEAE-cellulose chromatography and was characterized with respect to its amino acid composition and kinetic properties. Gel filtration and SDS-PAGE analysis showed that the enzyme was made up of a 70,000-Da peptide. Immunocytochemical studies on the localization of linamarase in cassava petioles showed sporadic positive staining in the phloem and intense staining in the thickened corners of the collenchyma cells of the cortex, suggesting the distribution of linamarase in laticifers as well as in the cell wall.