Ziro Nikuni

Crystallization and properties of pea glucosephosphate isomerase

Glucosephosphate isomerase (d-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9) of pea was isolated in the crystalline state in 14.5% yield from pea extract after 1500-fold purification. The molecular weight of the enzyme was estimated at 110 000 by ultracentrifugal analysis. The Km and molecular activity of the enzyme were determined as 2.7·10−4 M (Glc-6-P) and 165 000 in Tris-HCl buffer (pH 8.5) at 37°. The isomerization reaction was equilibrated in 65% Glc-6-P and 35% Fru-6-P at pH 7.5 at 37°. 6-Phosphogluconate competitively inhibited the reaction and its Ki was 1.3·10−5 M. The pH optimum of the reaction was found to be 8.5 in Tris-HCl buffer and 9.5 in glycine-NaCl-NaOH buffer. The maximal reaction rate was observed at 50° and the activation energy was calculated as 8100 cal. Sulfhydryl groups are not thought to be involved in its active center because the reaction was not inhibited by p-chloromercuribenzoate and monoiodoacetate. The enzyme was able to isomerize glucose into fructose in the presence of arsenate.

ADP-D-glucose—α-1,4-glucan α-4-glucosyltransferase in spinach chloroplasts Partial purification and some properties of the enzyme

Summary 1. A soluble enzyme which transfers glucosyl residues from ADPglucose to α -1,4-glucan has been obtained from spinach chloroplasts and partially purified 2. Some properties of the enzyme such as pH optimum, temperature optimum, nucleotide specificity, effectiveness of primers, etc ., have been investigated. Sulfhydryl groups may be important in the action of the enzyme 3. The present status of the enzyme in the research of starch biosynthesis is discussed.

Studies on the Protease of Pseudomonas :Part V. On the Role of Calcium in the Enzyme Production

The molecular structure of starch-paste was examined by means of Rontgen-method and the mechanism of the formation of the paste was discussed as follows: Starch grain is formed by amylose and amylopectine molecules which are arranged to micellar structure with radial direction. On heating with sufficient water, water molecules immerse into intra-micellar space as hydrate-water, when their kinetic energy becomes larger than the lattice energy of the micell. The long straight chain of amylose and the branched chains of amylopectine are surrounded by water molecules, but these chain molecules are not completely independent. They are combined each other by some holdings, and make up an elastic net-structure of the three dimensions. These holdings consist of either direct hydrogen-bridges between two hydroxyl-groups of the neighbouring starch molecules or indirect bridges by aid of some polar molecules as water or phosphoric acid molecules. Thus the complete paste formation is always accompanied with α-starch structure and no micellar structure is recognized by Rontgen-research. On cooling this paste, some chains assemble together to micellar structure and β-starch figures appear But the paste remaines almost unaltered by its net-structure with micells and remaining holdings.