Isolation and properties of carboxylesterases of the termite gut-associated fungus,Xylaria nigripes. k., and their identity from the host termite,Odentotermes horni. w., mid-gut carboxylesterases |
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| Institution: | 1. Department of Food Science, University of Massachusetts, Amherst, MA, USA;2. Department of Biology and Biomedical Sciences, Salve Regina University, Newport, RI, USA;3. Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA, USA;1. CNR-Istituto di Nanotecnologia (NANOTEC) – PLasMI Lab, Via Amendola 122/D, 70126 Bari, Italy;2. Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari \"Aldo Moro\", Via G. Amendola 165/A, 70126 Bari, Italy;1. K-herb Research Center, Korea Institute of Oriental Medicine, 1672 Yuseong-daero, Yuseong-gu, Daejeon 34054, Republic of Korea;2. Division of Nonclinical Studies, Korea Institute of Toxicology, 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea;1. Department of Biomedical Sciences, University of Padova, Viale G. Colombo 3, 35121 Padova, Italy;2. Institute of Biomolecular Chemistry, CNR, Padova Unit, Department of Chemistry, University of Padova, Via Marzolo 1, 35131 Padova, Italy |
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| Abstract: | - 1.1. The termite, Odentoiermes horni. W., houses three fungal species, viz. Xylaria nigripes, Termitomyces microcorpus, and Trichoderma (species not identified), in its gut. X. nigripes was found to possess higher esterase activity levels than the other two.
- 2.2. Four esterase enzymes, 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 homogeneity from the fungus X. nigripes, their biochemical and enzymological properties were determined, and compared with those of the previously characterized host termite mid-gut enzymes, TE-I and -II.
- 3.3. The Mr, ofFE-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 (Mr ~ 78.5 kDa). Each of the fungal enzymes, viz. FE-I to -IV, was a homodimer with subunits associated non-covalently. The subunit Mr, 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, = 40 kDa). Immunologically the fungal esterase enzymes, viz. FE-I to -IV, were different from those of the host termite mid-gut esterases, viz. TE-I and -II.
- 4.4. 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 kinetic reaction mechanism.
- 5.5. The two preliminary studies, i.e. the confinement of most esterase activity to the gut-tissue free from microorganisms and starvation of termites not leading to complete loss of esterase activity in the gut of the termites, suggested that there may not be any symbiotic relationship between termite, O. horni, and its gut associated microorganisms with regard to ester metabolism. Though the enzymes from the two sources were carboxylesterases, several of their properties were different and hence, they are different entities.
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