Effect of mutations at Glu160 and Val198 on the thermostability of lactate oxidase.

We have obtained two types of thermostable mutant lactate oxidase - one that exhibited an E-to-G point mutation at position 160 (E160G) through error-prone PCR-based random mutagenesis, and another that exhibited an E-to-G mutation at position 160 and a V-to-I mutation at position 198 (E160G/V198I) through DNA shuffling-based random mutagenesis - both of which we have previously reported. Our molecular modeling of lactate oxidase suggests that the substitution of G for E at position 160 reduces the electrostatic repulsion between the negative charges of E160 and E130 in the (beta/alpha)8 barrel structure, but a thermal-inactivation experiment on the five kinds of single-mutant lactate oxidase at position 160 (E160A, E160Q, E160H, E160R, and E160K) showed that the side-chain volume of the amino acid at position 160 mainly contributes to the thermostability of lactate oxidase. We also produced V198I single-mutant lactate oxidase through site-directed mutagenesis, and analysed the thermostability of wild-type, V198I, E160G, and E160G/V198I lactate oxidase enzymes. The half-life of E160G/V198I lactate oxidase at 70 degrees C was about three times longer than that of E160G lactate oxidase, and was about 20 times longer than that of wild-type lactate oxidase. In contrast, the thermostability of the V198I lactate oxidase was almost identical to that of wild-type lactate oxidase. This indicates that the V198I mutation alone does not affect lactate oxidase thermostability, but does affect it when combined with the E160G mutation.     

Spectral organization of the eye of a butterfly,Papilio

Journal of Comparative Physiology A - This review outlines our recent studies on the spectral organization of butterfly compound eyes, with emphasis on the Japanese yellow swallowtail butterfly,...     

Hepatic iron accumulation is not directly associated with induction of DNA strand breaks in the liver cells of Long-Evans Cinnamon (LEC) rats.

Effects of accumulation of copper and iron on induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats that spontaneously develop fulminant hepatitis. Copper and iron accumulated in the liver of LEC rats in an age-dependent manner from 4 to 15 weeks. Low-iron diet prevented the accumulation of iron in the liver, but did not prevent accumulation of copper. The amounts of DNA strand breaks that were estimated by comet assay in the liver cells of rats fed standard diet increased with age from 4 to 15 weeks. No significant differences were observed in the proportions of LEC rat liver cells without tail and the average lengths of tail momentum in the comet images between LEC rats that had been fed standard MF diet and low-iron diet. These results support the idea that accumulation of iron is not directly associated with the induction of DNA damage in the liver cells of LEC rats.     

Pseudanthias calloura (Teleostei: Perciformes), a new serranid fish from Palau, Central Pacific

A new anthine fish, Pseudanthias calloura, is described on the basis of three specimens from Palau. The new species differs from other congeners in having a complicated color pattern of the caudal fin and the following characters: moderately forked caudal fin; dorsal fin with 10 spines, the anterior ones being shorter than the rest, and with 16 soft rays; second anal spine shorter than the third; 19 pectoral rays; scales on lateral line 51 (holotype) to 53 (paratypes) in number; tongue without teeth; circumorbital rim with several fleshy projection on posterior part; a row of fine scales occurring asymmetrically behind alternate dorsal spines on both left and right sides; preopercle margin finely serrated; interopercle and subopercle margins smooth. Received: June 9, 1999 / Revised: September 23, 2000 / Accepted: February 23, 2001     

Scale-dependent effects of windthrow disturbance on forest arthropod communities

The effect of disturbance on local communities may operate within the context of the spatial landscape. We examined the scale-dependent effects of windthrow disturbance caused by a large typhoon on three arthropod communities in a temperate forest of Japan. Canopy arthropods were collected by beating foliage, forest-floor arthropods were collected by sweeping the vegetation, and flying arthropods were collected in Malaise traps. To assess the “functional spatial scale” at which arthropods responded to tree-fall disturbance, the gap rate was quantified at different spatial scales by sequentially enlarging the radius of a circular landscape sector in 10-m increments from 10 to 500 m. We then analyzed the responses of order richness and abundance to the gap rate for each arthropod community. The spatial scale of the significant best-fitting model, which was selected from the models fitted to the gap rate at stepwise spatial scales, was regarded as the arthropod-specific functional spatial scale. Arthropod order richness was not dependent on the gap rate. In contrast, arthropod order abundance depended significantly on the gap rate in many orders, but varied in the response direction and functional spatial scale. These order-specific, scale-dependent responses to tree-fall gaps could complicate interactions among organisms, leading to complex community organization. An understanding of the spatial processes that link the use of space by organisms with the spatial scale at which ecological processes are experienced is required to elucidate the responses of populations, communities, and biotic interactions to disturbances in a spatial landscape context.     

C-terminal cleavage of the LH1 <Emphasis Type="Italic">α</Emphasis>-polypeptide in the Sr<Superscript>2+</Superscript>-cultured <Emphasis Type="Italic">Thermochromatium tepidum</Emphasis>

The light-harvesting 1 reaction center (LH1-RC) complex in the thermophilic purple sulfur bacterium Thermochromatium (Tch.) tepidum binds Ca ions as cofactors, and Ca-binding is largely involved in its characteristic Q_y absorption at 915 nm and enhanced thermostability. Ca²⁺ can be biosynthetically replaced by Sr²⁺ in growing cultures of Tch. tepidum. However, the resulting Sr²⁺-substituted LH1-RC complexes in such cells do not display the absorption maximum and thermostability of those from Ca²⁺-grown cells, signaling that inherent structural differences exist in the LH1 complexes between the Ca²⁺- and Sr²⁺-cultured cells. In this study, we examined the effects of the biosynthetic Sr²⁺-substitution and limited proteolysis on the spectral properties and thermostability of the Tch. tepidum LH1-RC complex. Preferential truncation of two consecutive, positively charged Lys residues at the C-terminus of the LH1 α-polypeptide was observed for the Sr²⁺-cultured cells. A proportion of the truncated LH1 α-polypeptide increased during repeated subculturing in the Sr²⁺-substituted medium. This result suggests that the truncation is a biochemical adaptation to reduce the electrostatic interactions and/or steric repulsion at the C-terminus when Sr²⁺ substitutes for Ca²⁺ in the LH1 complex. Limited proteolysis of the native Ca²⁺-LH1 complex with lysyl protease revealed selective truncations at the Lys residues in both C- and N-terminal extensions of the α- and β-polypeptides. The spectral properties and thermostability of the partially digested native LH1-RC complexes were similar to those of the biosynthetically Sr²⁺-substituted LH1-RC complexes in their Ca²⁺-bound forms. Based on these findings, we propose that the C-terminal domain of the LH1 α-polypeptide plays important roles in retaining proper structure and function of the LH1-RC complex in Tch. tepidum.