Characterization and purification of polymorphic arylalkylamine N-acetyltransferase from the American cockroach, Periplaneta americana.

We separated two forms of arylalkylamine N-acetyltransferase (AANAT) from various organs of the American cockroach, Periplaneta americana. Both forms of the enzyme had an equivalent molecular mass of 28 kDa. One form isolated from the testicular accessory glands had high enzyme activity at acidic pHs. The isoelectric point was 5-6 and the substrate specificity was wider than the other type. The other isolated form from female midguts had a higher level of enzyme activity at basic pHs. These findings suggested that P. americana contains polymorphic AANAT, as is the case in Drosophila melanogaster. These forms differed not only in pH specificity, and substrate specificity but in chromatographic behavior and kinetic properties. Most of the organs we examined contained a mixture of the two forms since two types of AANAT activity were separated in different chromatographic fractions when two pH conditions were used for activity measurement.     

Purification and properties of a lytic enzyme from the cell wall of Chlorella ellipsoidea C-87

Cell wall lytic activity was detected in the culture medium and cell wall of 1AM Chlorella ellipsoidea C-87. The enzymes of both fractions had their highest activity at pH 5. The lytic activity bound to the cell wall consisted of a polysaccharide releasing enzyme, an exo-type enzyme releasing disaccharide, and glucosidase; but only the polysaccharide releasing enzyme was solubilized by lithium chloride. A polysaccharide releasing enzyme with a molecular weight around 40 kDa was isolated from the culture medium. Hemicellulose is degraded by the polysaccharide releasing enzyme, and the rigid wall by the exo-type enzyme.     

Crystal structure of the C-terminal domain of Mu phage central spike and functions of bound calcium ion

Bacteriophage Mu, which has a contractile tail, is one of the most famous genus of Myoviridae. It has a wide host range and is thought to contribute to horizontal gene transfer. The Myoviridae infection process is initiated by adhesion to the host surface. The phage then penetrates the host cell membrane using its tail to inject its genetic material into the host. In this penetration process, Myoviridae phages are proposed to puncture the membrane of the host cell using a central spike located beneath its baseplate. The central spike of the Mu phage is thought to be composed of gene 45 product (gp45), which has a significant sequence homology with the central spike of P2 phage (gpV). We determined the crystal structure of shortened Mu gp45Δ1-91 (Arg92–Gln197) at 1.5 Å resolution and showed that Mu gp45 is a needlelike structure that punctures the membrane. The apex of Mu gp45 and that of P2 gpV contained iron, chloride, and calcium ions. Although the C-terminal domain of Mu gp45 was sufficient for binding to the E. coli membrane, a mutant D188A, in which the Asp amino acid residue that coordinates the calcium ion was replaced by Ala, did not exhibit a propensity to bind to the membrane. Therefore, we concluded that calcium ion played an important role in interaction with the host cell membrane.