title: Metal as a novel type of the enzyme substrate. Metallic cadmium photogenerated in the system CdS-formate as a substrate of the NAD-dependent hydrogenase.
abstract: The process of NAD+ photoreduction under the coupled action of CdS semiconductor and NAD-dependent hydrogenase from hydrogen-oxidizing bacterium Alcaligenes eutrophus may be divided into light and dark stages. At the first stage, illumination of the system leads to the photooxidation of the sacrificial electron donor and results in the reduction of the semiconductor surface. At the second dark stage NAD+ is reduced to NADH in the presence of hydrogenase. Atoms of metallic Cd(0) are shown to be the true substrate of the enzymatic reaction. The prerequisite for the electron transfer from Cd(0) to hydrogenase is enzyme adsorption on the semiconductor surface. The redox center of the hydrogenase reacting with Cd(0) atoms resides on the flavin-containing heterodimer of the protein. The activity of the hydrogenase immobilized on CdS in the reaction of NAD+ reduction by metallic Cd is close to the enzyme activity with the physiological substrates in solution. Thus, the first example of a metal being the substrate of the enzymatic process is presented.
authors.affiliation: A.N. Bakh Institute of Biochemistry, Russian Academy of Sciences, Moscow.
authors.forename: I A
authors.initials: IA
authors.lastname: Shumilin
authors.forename: V V
authors.initials: VV
authors.lastname: Nikandrov
authors.forename: A A
authors.initials: AA
authors.lastname: Krasnovsky
authors.forename: V O
authors.initials: VO
authors.lastname: Popov
mesh_terms: D000421:Alcaligenes / Q000201:enzymology; D002104:Cadmium / Q000378:metabolism*; D019187:Cadmium Compounds; D005561:Formates; D006864:Hydrogenase / Q000378:metabolism*; D008027:Light; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D013379:Substrate Specificity; D013440:Sulfides
chemical_list: D019187:Cadmium Compounds; D005561:Formates; D013440:Sulfides; D002104:Cadmium; C034939:cadmium sulfide; D009243:NAD; D006864:Hydrogenase