ISOLATION AND PROPERTIES OF CARBOXYLESTERASES OF THE TERMITE GUT-ASSOCIATED FUNGUS, XYLARIA-NIGRIPES K, AND THEIR IDENTITY FROM THE HOST TERMITE, ODENTOTERMES-HORNI W, MIDGUT CARBOXYLESTERASES

1. The termite, Odentotermes horni. W., houses three fungal species, v iz. Xylaria nigripes, Termitomyces microcorpus, and Trichoderma (speci es not identified), in its gut. X. nigripes was found to possess highe r esterase activity levels than the other two. 2. Four esterase enzyme s, viz. FE-I, -II, -III and -IV, with pI values 5.1, 5.25, 5.4 and 5.6 , respectively, were identified, isolated and purified to apparent hom ogeneity from the fungus X. nigripes, their biochemical and enzymologi cal properties were determined, and compared with those of the previou sly characterized host termite mid-gut enzymes, TE-I and -II. 3. The M (r) of FE-I and -II was 85.1 kDa and those of FE-III and -IV was 87.5 kDa. However, TE-I and -II were relatively smaller (M(r) approximately 78.5 kDa). Each of the fungal enzymes, viz. FE-I to -IV, was a homodi mer with subunits associated non-covalently. The subunit M(r) were 42. 6 kDa for FE-I and -II, and 43.7 kDa for FE-III and -IV. On the other hand, the termite mid-gut enzymes, TE-I and -II, were also homodimeric , but the subunits were associated covalently (subunit M(r) = 40 kDa). Immunologically the fungal esterase enzymes, viz. FE-I to -IV, were d ifferent from those of the host termite mid-gut esterases, viz. TE-I a nd -II. 4. The substrate specificity and inhibitor sensitivity studies classify these enzymes, i.e. FE-I to -IV, as carboxylesterases (EC 3. 1.1.1). Steady-state product inhibition kinetics suggested; an ordered release of products, i.e. alcohol followed by acid, and a Uni-Bi kine tic reaction mechanism. 5. The two preliminary studies, i.e. the confi nement of most esterase activity to the gut-tissue free from microorga nisms and starvation of termites not leading to complete loss of ester ase activity in the gut of the termites, suggested that there may not be any symbiotic relationship between termite, O. horni, and its gut a ssociated microorganisms with regard to ester metabolism. Though the e nzymes from the two sources were carboxylesterases, several of their p roperties were different and hence, they are different entities.