Petiole, stem and root cortex of cassava as new sources of linamarase
1986
Thidarat Eksittikul | Montri Chulavatnatol (Mahidol Univ., Bangkok (Thailand). Faculty of Science. Dept. of Biochemistry)
Cassava (Manihot esculenta Crantz) is an important food in the developing world. However, extensive consumption of cassava roots may run the risk of cyanide toxicity. Cassava root contains two cyanogenic glucosides, linamarin as main component and lotaustalin, and their degrading enzyme linamarase (or beta-D-glucoside glycohydrolase E.C. 3.2.1.21). Hydrolysis of these glucosides by linamarase releases hydrogen cyanide when the roots are damaged. The enzyme has been partially purified from cassava root parenchyma (1) and used for determination of cyanide in cassava trading and research. Thailand is the second largest cassava-producer in the world. Much stems and leaves are by-products from cassava plantation. So we decided to look for linamarase in these by-products. The specific activities of the enzyme in petiole, stem and root cortex were found to be higher than that in the root parenchyma. The enzyme was separated from other proteins by Sepharose 6B column and found to have a native Mr of 600,000 (for petiole and stem). By this technique, the root cortex enzyme was partially resolved into two peaks with Mr of 570,000 and 400,000. By SDS-PAGE, the subunit Mr of each enzyme preparation was found to be 63,000. From chromatofocusing column in the pH range of 5 to 1, the enzyme form each source was separated into three isozymes with pI 4.3, 3.3 and 2.9. The pH optimum, Km and Vmax values of these enzyme preparations were also compared. The findings suggested that petiole, stem and root cortex of cassava were possible new sources of linamarase. Supported by a grant of USAID/PSTC 936-5542-G-00-6028-00 and MOSTE.
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