Inheritance of heat stable esterase in near isogenic lines and functional classification of esterase in silkworm Bombyx mori

Abstract

Esterases are ubiquitous in living organisms and perform multiple functions in animals, plants, insects and microorganisms. Insect esterases broadly perform physiological and defense functions. The present work aims towards identifying heat stable esterase in the hemolymph of near isogenic lines (NILs) and their parents, and further to classify esterases based on substrate-inhibition reactions in silkworm, Bombyx mori. Five different α-esterases viz. Est-1, Est-2, Est-3, Est-4 and Est-5 were observed in this study. Of them, Est-1 and Est-2 were monomorphic and, Est-3, Est-4 and Est-5 were polymorphic. Heat stability studies revealed Est-2 and Est-3 as heat stable and, Est-1, Est-4 and Est-5 as heat liable. Through inhibition analysis, Est-1 was identified as cholinesterase and Est-5 as carboxylesterase because their activity was totally inhibited, respectively, by eserine sulphate and phenylmethylsulfonyl fluoride (PMSF) while Est-3 was inhibited by both the inhibitors. The Est-2 and Est-4 were unaffected by both PMSF and eserine sulphate. The isozyme patterns of breed specific as well as heat stable esterases supports the variations in the survival percentage of silkworm breeds at high temperatures. This study enhances the knowledge on esterase-mediated thermotolerance in B. mori.