title: Liposomal encapsulation of yeast alcohol dehydrogenase with cofactor for stabilization of the enzyme structure and activity.
abstract: Yeast alcohol dehydrogenase (YADH) with its cofactor nicotinamide adenine dinucleotide (NAD+) could be stably encapsulated in liposomes composed of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine). The YADH- and NAD+-containing liposomes (YADH-NADL) were 100 nm in mean diameter. The liposomal YADH and NAD+ concentrations were 2.3 mg/mL and 3.9 mM, respectively. A synergistic effect of the liposomal encapsulation and the presence of NAD+ was examined on the thermal stability of YADH at 45 and 50 degrees C. The enzyme stability of the YADH-NADL was compared to the stabilities of the liposomal YADH (YADHL) containing 3.3 mg/mL YADH without NAD+ as well as the free YADH with and without NAD+. Free YADH was increasingly deactivated during its incubation at 45 degrees C for 2 h with decrease of the enzyme concentration from 3.3 to 0.01 mg/mL because of the dissociation of tetrameric YADH into its subunits. At that temperature, the coexistence of free NAD+ at 3.9 mM improved the stability of free YADH at 2.3 mg/mL through forming their thermostable complex, although the stabilization effect of NAD+ was lowered at 50 degrees C. The turbidity measurements for the above free YADH solution with and without NAD+ revealed that the change in the enzyme tertiary structure was much more pronounced at 50 degrees C than at 45 degrees C even in the presence of NAD+. This suggests that YADH was readily deactivated in free solution due to a decrease in the inherent affinity of YADH with NAD+. On the other hand, both liposomal enzyme systems, YADH-NADL and YADHL, showed stabilities at both 45 and 50 degrees C much higher than those of the above free enzyme systems, YADH/NAD+ and YADH. These results imply that the liposome membranes stabilized the enzyme tertiary and thus quaternary structures. Furthermore, the enzyme activity of the YADH-NADL showed a stability higher than that of the YADHL with a more remarkable effect of NAD+ at 50 degrees C than at 45 degrees C. This was considered to be because even at 50 degrees C the stabilization effect of lipid membranes on the tertiary and quaternary structures of the liposomal YADH allowed the enzyme to form its thermostable complex with NAD+ in liposomes.
authors.affiliation: Departments of Applied Molecular Bioscience, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan. yosimoto@yamaguchi-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Yoshimoto
authors.forename: Mami
authors.initials: M
authors.lastname: Sato
authors.forename: Noriko
authors.initials: N
authors.lastname: Yoshimoto
authors.forename: Katsumi
authors.initials: K
authors.lastname: Nakao
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D004789:Enzyme Activation; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry; D007527:Isoenzymes / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D020099:Coated Materials, Biocompatible; D004800:Enzymes, Immobilized; D007527:Isoenzymes; D008081:Liposomes; D000426:Alcohol Dehydrogenase