Weak Light-Induced Oxygen Consumption Observed during Photoreactivation Is Coupled to the Recovery of Oxygen Evolving Activity

During photoreactivation of the O₂-evolving center in Tris-inactivated/Mn-depletedthylakoids, a slow O₂-consumption occurred. This O₂-consumptionbecame detectable when the O₂-evolving activity of thylakoidswas inactivated by Tris-treatment and decreased as photoreactivationproceeded. The O₂-consumption and photoreactivation similarlyrequired Mn²⁺ at µM levels in addition to PSII electrondonors and shared severa common characteristics. Stimulationof O₂-consumption and photoreactivation by these cofactors werealways accompanied by enhancement in chlorophyll fluorescenceinduction, suggesting the involvement of a Mehler-type reactionin photoreactivation. Although the electron transport due tothis O₂-consumption was rapid enough to oxidize 4 Mn²⁺ ionsto reconstitute the tetranuclear Mn-cluster in each O₂-evolvingcenter in a few seconds, actual recovery of O₂-evolving activityoccurred more slowly in a few minutes. It was inferred thatphotoreactivation in Tris-inactivated thylakoids is not a simplephotooxidation of Mn2²⁺ but involves more complicated processeswhich are coupled to the Mehlertype electron transport fromPSII to oxygen via PSI. (Received July 11, 1994; Accepted August 23, 1996)     

Binding of nonamer peptides to three HLA-B51 molecules which differ by a single amino acid substitution in the A-pocket

The interaction between 9-mer peptides and HLA-B51 molecules was investigated by quantitative peptide binding assay using RMA-S cell expressing human β2-microglobulin and HLA-B51 molecules. Of 147 chemically synthesized 9-mer peptides possessing two anchor residues corresponding to the motif of HLA-B^*5101 binding self-peptides, 27 paptides bound to HLA-B^*5101 molecules. Pro and Ala at position 2 as well as Ile at position 9 were confirmed to be main anchor residues, while Gly at position 2 as well as Val, Leu, and Met at position 9 were weak anchor residues for HLA-B^*5101. The A-pocket is suspected to have a critical role in peptide binding to MHC class I molecules because this pocket corresponds to the N-terminus of peptides and has a strong hydrogen bond formed by conserved Tyr residues. Further analysis of peptide binding to HLA-B^*5102 and B^*5103 molecules showed that a single amino acid substitution of Tyor for His at residue 171(B^*5102) and that of Gly for Trp at residue 167 (B^*5103) has a minimum effect in HLA-B51-peptide binding. Since previous studies showed that some HLA-B51 alloreactive CTL clones failed to kill the cells expressing HLA-B^*5102 or HLA-B^*5103, these results imply that the structural change of the A-pocket among HLA-B51 subtypes causes a critical conformational change of the epitope for TCR recognition rather than influences the interaction between peptides and MHC class I molecules.     

Isolation of a gene essential for biosynthesis of the lipopeptide antibiotics plipastatin B1 and surfactin in Bacillus subtilis YB8

Bacillus subtilis YB8 was found to produce the lipopeptide antibiotics surfactin and plipastatin B1. A gene, lpa-8, required for the production of both lipopeptides was cloned from strain YB8. When this gene was inactivated in strain YB8, neither surfactin nor plipastatin B1 was produced. However, the defective strain transformed with an intact lpa-8 gene had restored ability to produce both peptides. Nucleotide sequence analysis of the region essential for the production of the peptides revealed the presence of a large open reading frame. The deduced amino acid sequence of lpa-8 (224 amino acid residues) showed sequence similarity to that of sfp (from surfactin-producing B. subtilis), lpa-14 (from iturin A- and surfactin-producing B. subtilis), psf-1 (from surfactin-producing Bacillus pumilus), gsp (from gramicidin-S-producing Bacillus brevis), and entD (from siderophore-enterobactin-producing Escherichia coli), which are able to complement a defect in the sfp gene and promote production of the lipopeptide antibiotic surfactin. The sequence similarity among these proteins and the product similarity of cyclic peptides suggests that they might be involved in the biosynthesis or secretion of the peptides. Received: 14 July 1995 / Accepted: 22 December 1995     

Changes in organic matter composition of forest soil treated with a large amount of urea to promote ammonia fungi and the abilities of these fungi to decompose organic matter

Organic matter composition (lignin, holocellulose, 50% (v/v) methanol extract, water-soluble carbohydrate (WSC) and phenolics (WSP), petroleum ether extract, and ash) of A₀ layer soil treated with 700 g/m² of urea to promote ammonia fungi was investigated in a Japanese red pine (Pinus densiflora) forest. Nine species of fungi were found during the study period of 18 months after the treatment. Of these, seven species belong to the ammonia fungi. WSC content of the treated soil was lower than that of the control. Methanol extract content increased initially after the treatment, then decreased to below the control level. There were no consistent differences in other components between the treated plot and the control. The abilities to decompose cellulose, lignin, chitin, protein and lipid in 18 strains in 10 species of the ammonia fungi were also screened. Cellulose was not lysed byPseudombrophila deerata, Hebeloma spp. andLaccaria bicolor. Strong lignolytic activity was shown byLyophyllum tylicolor, Coprinus echinosporus andP. deerata. Chitin was decomposed byAmblyosporium botrytis, L. tylicolor, C. echinosporus andHebeloma vinosophyllum. All strains possessed proteolytic and lipolytic activities. Supply of glucose to the culture media resulted in weaker enzyme activities except for lignolytic ability.     

Aspergillus taichungensis,a new species from Taiwan

Aspergillus taichungensis isolated from a soil sample collected in Taiwan is described as a new species. The new species is characterized by its restricted growth on Czapek's and malt extract agars and its white to light yellow colonies, radiate conidial heads, smooth and often diminutive conidiophores, hemispherical to elongate vesicles with biseriate aspergilla (conidiogenous cells), globose, micro-verrucose conidia and dark brown sclerotia. The species somewhat resemblesA. versicolor, A. terreus andA. flavipes, but differs in cultural and morphological details, and is considered to represent an interface species in the subgenusNidulantes.     

Transformation of fibroblasts into endothelial cells during angiogenesis

Light-and electron-microscopic autoradiography have been used to study fibroblast transformation into endothelial cells in the formation of new blood vessels during wound healing in rabbit ear chambers. When cultured fibroblasts labeled with tritium thymidine were transplanted autologously into the chambers, newly formed blood vessels contained endothelial cells labeled with tritium thymidine. This result suggests that fibroblasts play a pivotal role in angiogenesis, as progenitors of endothelial cells in newly formed blood vessels.