Archives of Biochemistry and Biophysics

active HNLs lacking FAD are found in some cyanogenic a-Hydroxynitrile lyase (HNL, acetone-cyanohydrin plants, e.g., flax, sorghum, rubber tree, and cassava. lyase, EC 4.1.2.37) was purified to homogeneity from Both types of HNLs show substrate specificity for eipetioles of cassava (Manihot esculenta Crantz). The puther aromatic or aliphatic cyanohydrins. rified HNL is a homotetramer with a subunit molecular Cassava HNL has been isolated from young leaf tisweight of 25,600 and an isoelectric point of 4.7. The sue in other laboratories. An earlier study has reported HNL activity exhibits a pH optimum of 5.0 and is stable that cassava HNL exhibits a subunit molecular weight in the pH range of 6 to 11. The petiole HNL shows a of 15,000 and different degrees of aggregation (dimer to simple Michaelis–Menten kinetics with Km for acetone octomer) (11). A later study has shown a larger subunit cyanohydrin of 4.0{ 0.9 mM and Vmax of 46.2{ 5.0mmol/ molecular weight of 25,500 (12). A recent study shows min/mg. Several alcohols, aldehydes, and ketones inthat cassava leaf HNL is a trimer with a subunit molechibit the HNL activity. The alcohols and ketones are ular weight of 28,500 (13). It also exhibits a complex competitive inhibitors, whereas the aldehydes are (non-Michaelis–Menten) kinetics which has been imnoncompetitive inhibitors. On the basis of Ki values, plied to be related to the aggregation stages of the subinhibitors with 4 carbons are more potent than those units (13). Furthermore, the report also describes its with the same functional groups but having fewer or cDNA sequence. more than 4 carbons. q 1996 Academic Press, Inc. In this study, we have found that cassava petioles