D(-)-beta-Hydroxybutyrate dehydrogenase was purified from Zoogloea ramigera I-16-M to electrophoretic homogeneity. The molecular weight of the enzyme as determined by Sephadex G-200 gel filtration was 112,000, and the monomer molecular weight estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate was 28,000, indicating that the native enzyme is a tetramer with four identical subunits. The enzyme showed a pH optimum at 8.0 in the oxidation reaction, and a broad pH optimum (5.5-7.5) in the reduction reaction. The Km values for D(-)-beta-hydroxybutyrate and NAD in the oxidation reaction were 3.2 X 10(-4) M and 5.7 X 10(-5) M, respectively. The Km value for acetoacetate in the reduction reaction was 1.5 X 10(-4) M and that for NADH was 1.5 X 10(-5) M. Acetyl CoA, D-lactate, and 2-hydroxybutyrate were effective inhibitors for the oxidation of D(-)-beta-hydroxybutyrate. The enzyme was sensitive to the inhibitory actions of sulfhydryl reagents such as p-chloromercuribenzoic acid, 5,5'-dithiobis(2-nitrobenzoic acid) and HgCl2.

An AlN layer with tensile strain along the a-axis was grown on a (0001) 6H-SiC substrate with a (GaN/AlN) buffer layer by metal-organic vapor-phase epitaxy using an alternating source feeding technique. It was experimentally demonstrated that the strain in the AlN layer was affected by the buffer layer structure. On the other hand, the AlN layer grown directly on a substrate without the buffer layer exhibits compressive strain along the a-axis. Strain control in the AlN layer by adjusting the buffer layer structure is proposed.

No abstract