Dihydrodipicolinate synthase (EC 4.2.1.52), the first enzyme unique to lysine biosynthesis in bacteria and higher plants, has been purified to homogeneity from etiolated pea (Pisum sativum) seedlings using a combination of conventional and affinity chromatographic steps. This is the first report on a homogeneous preparation of native dihydrodipicolinate synthase from a plant source. The pea dihydrodipicolinate synthase has an apparent molecular weight of 127,000 and is composed of three identical subunits of 43,000 as determined by gel filtration and crosslinking experiments. The tnmenc quaternary structure resembles the trimenc structure of other aldolases, such as 2-keto-3-deoxy-6-phosphogluconic acid aldolase, which catalyze similar aldol condensations. The amino acid compositions of dihydrodipicolinate synthase from pea and Escherichia coli are similar, the most significant difference concems the methionine content: dihydrodipicolinate synthase from pea contains 22 moles of methionine residue per mole of native protein, contrary to the E. coli enzyme, which does not contain this amino acid at all. Dihydrodipicolinate synthase from pea is highly specific for the substrates pyruvate and L-aspartate-fl-semialdehyde; it follows Michaelis-Menten kinetics for both substrates. The pyruvate and L-aspartate-ft-semialdehyde have Michaelis constant values of 1.70 and 0.40 millimolar, respectively. L-Lysine, S-(2-aminoethyl)-L-cysteine, and La-(2-aminoethoxyvinyl)glycine are strong allostenc inhibitors of the enzyme with 50% inhibitory values of 20, 160, and 155 millimolar, respectively. The inhibition by L-lysine and L-a-(2-aminoethoxyvinyl)glycine is noncompetitive towards L-aspartateBl-semialdehyde, whereas S-(2-aminoethyl)-L-cysteine inhibits dihydrodipicolinate synthase competitively with respect to L-aspartate-jt-semialdehyde. Furthermore, the addition of (2R,3S,6S)-2,6-diamino-3-hydroxy-heptandioic acid (1.2 millimolar) and (2S,6R/S)-2,6-diamino-6-phosphono-hexanic acid (1.2 millimolar) activates dihydrodipicolinate synthase from pea by a factor of 1.4 and 1.2, respectively. This is the first reported activation process found for dihydrodipicolinate synthase.

The attachment of three strains of Acetobacter aceti (ATCC 23747, ATCC 23748, NCIB 8246), with or without capsule, cultured under different conditions has been investigated in solutions of controlled pH. Various materials (silicates, organic polymers) have been used as supports, and the results have been related to the surface properties of the cells and supports. Cells that do not have a capsule do not adhere to the tested materials, whatever their hydrophobicity, unless the latter are previously treated by ferric ions to make their surface less negative. Cells that possess a capsule adhere to non-treated supports. In all cases the highest density of the adhering cellular film is obtained when the electrostatic repulsions between a cell and the support and between cells are reduced (surface charge of the support less negative, lower pH). The capsule influences adhesion by affecting the interplay between electrostatic interactions and hydrophobic bonding; moreover, capsule polymers may favor adhesion by acting as binding agent. The occurrence of cell flocculation gives rise to greater heterogeneity and lower cell density in the film of adhering cells.