Biochemical properties of thiaminase, a toxic enzyme in the gut of grasshoppers (Zonocerus variegatus Linn)

Abstract

The variegated grasshopper, Zonocerus variegatus (Linn) (Orthoptera: Pyrgomorphidae) is eaten mostly in the South western region of Nigeria. Thiaminase is a toxic enzyme present in some foods. The activity of thiaminase in the gut of Zonocerus variegatus is described. The enzyme was isolated using DEAE- Cellulose  ion exchange chromatography and gel filtration on Biogel P-100. The enzyme had a specific activity of 7.9 unit per milligram of protein. The enzyme exhibited a maximal activity at pH 8.0 and K_m of 5 and 25 µM for thiamine and aniline respectively. The substrate specificity showed that the thiaminase from Z. variegatus was specific for thiamine and aniline as substrates. The optimum temperature of Z. variegatus thiaminase was 50^oC. The native molecular weight of the enzyme as determined by gel filtration was 102,000. The amino acids markedly enhanced the activity of the enzyme. The enzyme was activated by Mn²⁺, Ni²⁺ and Hg²⁺ but inhibited by Na⁺, NH₄⁺, Co²⁺ and Zn²⁺. 2-mercaptoethanol and 6-amino hexanoic acid completely inhibited the thiaminase. Z. variegatus should be prepared using extensive and prolong cooking to avoid suffering from thiamine deficiency.