Reserach Outline

List of Publication

Mita Lab. English

Mita Lab. Japanese

Under construction.

Origins of Life, Organic Geochemistry, Astrobiology, Protein chemistry and Biomaterials.

I study the life by organic chemical analyses, especially, amino acids, peptide and proteins.

1. Formation of amino acids and peptides in the prebiotic conditions. 2. Organic analyses of sedimentary rocks, meteorites, and small solar bodies. 3. Studies of structure-function relationship of proteins. 4. Formation and function of biomaterials.

1. Formation of amino acids and peptides in the prebiotic conditions.

Prebiotic formation of polyamino acids in molten urea. We demonstrate a novel thermal polymerization in molten urea of alkylamino acids (i.e. glycine, alanine, b-alanine, a-aminobutyric acid, valine, norvaline, leucine, and norleucine) which had been thought to be incapable of undergoing thermal polymerization. Major products in the reaction mixture were three different types of polyamino acid derivatives: N-carbamoylpolyamino acids, polyamino acids containing a hydantoin ring at the N-terminal position, and unidentified derivatives whose molecular weights were larger by 78 relative to those of the corresponding peptide forms. The polymerization reaction occurred by taking advantage of molten urea's high polarity as well as its dehydrating ability. Under the presumed prebiotic conditions employed here, many types of amino acids were thus revealed to undergo thermal polymerization. Kinetic study of abiotic amino acid formation by uv irradiation. Glycine was produced in a solution of 2-aminoethanol, methylamine, ethylamine, or acetonitrile by uv irradiation. The concentrations of the reactants and glycine were analyzed under six different conditions. Each reaction was assumed to be a first-order reaction. Then, the rate constant of the degradation of the reactants, and also those of the formation and degradation of glycine were calculated. Each rate constant of the glycine degradation was at least 10 times larger than that of the glycine formation. Glycine did not accumulate but instead disappeared on prolonged uv irradiation when the reactants were supplied to the environment only once at initiation of the irradiation.

2. Organic analyses of sedimentary rocks, meteorites, and small solar bodies.

Search for extraterrestrial amino acids in the K/T boundary sediments at Kawaruppu. Amino acids in the K/T boundary sediments at Kawaruppu were analyzed. A maximum of eight kinds of amino acids including diagenetically unstable serine and threonine was detected in the water extracts at most at one nmol g-1 sample level. The number of kinds and quantities of amino acids from the HCl extracts were smaller than those from the water extracts. The D/L ratios of these amino acids indicate that they are not so old as 65 million years. a-Aminoisobutyric acid and isovaline were not detected in any samples, in contrast to the previous study of amino acids in the K/T boundary at Stevns Klint, Denmark. Amino acids of possible extraterrestrial and/or 65 million-year-old terrestrial in origin were not present in the K/T boundary at Kawaruppu. Three plausible explanations for the different results between the present and previous studies are discussed in the text. In addition, results of this study do not support the cometary dust origin proposed for the presence of the two extraterrestrial amino acids at Stevns Klint. Amino acids in the Recent Tokyo Bay sediments. Two non-proteinaceous amino acids, a-aminoisobutyric acid and isovaline were found in the Recent Tokyo Bay sediments together with several proteinaceous amino acids. Concentrations of the two non-proteinaceous acids were approximately 1 nmol per g of dry sediment, and the proteinaceous amino acids were several hundred to slightly over one thousand nmol per g. Isovaline was found to be nearly racemic, whereas the proteinaceous amino acids were predominantly in the L-form. The two non-proteinaceous amino acids was not considered to be of extraterrestrial origin as suggested by the study of the K/T boundary sediments at Stevns Klint and proposed a terrestrial origin. The source of the two non-proteinaceous amino acids is not biological because the isovaline is racemic. They may come from industrial wastewater containing C-5 substituted hydantoins, which then hydrolyzed to give a-aminoisobutyric acid and racemic isovaline. Organic compound analyses of condensed water in the MIR space station. Amino acids were found in the condensed water samples collected from the inside of MIR indicating the presence of microorganisms probably grown in orbit. Aromatic alcohols and aldehydes were found in the benzene extracts of the water samples and they were likely from the sterilants and fragrances used in MIR. Present analysis of the benzene extracts failed to find a signature of the fire on February 23, 1997 that took place inside MIR.

3. Studies of structure-function relationship of proteins.

Complex formation of 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphyrin with G-quadruplex DNA A water-soluble cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H- porphyrin (TmPyP4), has been under extensive study because of its unique physicochemical properties leading to interactions with nucleic acids, as well as its therapeutic application. Complex formation between TmPyP4 and parallel G-quadruplex DNA formed from a single repeat sequence of the human telomere, d(TTAGGG), has been characterized in order to elucidate the mode of molecular recognition between TmPyP4 and the DNA. The study demonstrated that TmPyP4 intercalates into the A3pG4 step of (d(TTAGGG))4 with a association constant of 6.2 �L 106 M-1 and a stoichiometric ratio of 1:1. The binding of TmPyP4 to the A3pG4 step of (d(TTAGGG))4 was found to be stabilized by the p-p stacking interaction of the porphyrin ring of TmPyP4 with the G4-quartet as well as the A3 bases of the G-quadruplex DNA. These findings provide novel insights for the design of porphyrin derivatives that bind to DNA with high affinity and specificity.

4. Formation and function of biomaterials.

Estimating age of amber and artificial synthesis of amber. Solid-state 13CNMR characterization of cross-linkage formation between the exocyclic methylene groups of labdane polymers in amber demonstrated that the process is an apparent first-order reaction with a half-life of ca 13 million years. And we try to synthesize amber from the resins.

Project

1. Asteroid Explorer 'HAYABUSA' and 'HAYABUSA2' 2. Japanese Astrobiology Experiment 'TANPOPO' on ISS. 3. Japan Astrobiology Mars Project (JAMP): Search for methane-oxidizing microbes on Mars surface. 4. Organic and biological survey on Antarctic as an extreme environment.