Hakobu Nakamura

The active part of the [6]-gingerol molecule in mutagenesis

A study was performed to discover the active part in mutagenesis of [6]-gingerol, a mutagen contained in ginger Zingiber officinale (Nakamura and Yamamoto, 1982). [6]-Shogaol was isolated from the ginger by column chromatography on silica gel. [6]-Shogaol was much less mutagenic (1 X 10(3) revertants/10(8) viable cells/700 microM) than [6]-gingerol (1 X 10(7) of the same units). Mutation frequencies of their related compounds were 4 X 10(1) for zingerone, 1 X 10(7) for 3-hydroxymyristic acid and 3 X 10(2) for 12-hydroxystearic acid. Curcumin, and myristic, stearic and oleic acids had no mutagenicity; and diacetone alcohol and butyroin were suppressible for mutation. It was inferred from these results that the active part of [6]-gingerol was the aliphatic chain moiety containing a hydroxy group.

Cellular differentiation in the process of generation of the eukaryotic cell.

Primitive atmosphere of the earth did not contain oxygen gas (O2) when the proto-cells were generated successfully as the resut of chemical evolution and then evolved. Therefore, they first had acquired anaerobic energy metabolism, fermentation. The cellular metabolisms have often been formed by reorganizing to combine or recombinate between pre-existing metabolisms and newly born bioreactions. Photosynthetic metabolism in eukaryotic chloroplast consists of an electron-transfer photosystem and a fermentative reductive pentose phosphate cycle. On the other hand, O2-respiration of eukaryotic mitochondrion is made of Embden-Meyerhof (EM) pathway and tricarboxylic acid cycle, which originate from a connection of fermentative metabolisms, and an electron-transfer respiratory chain, which has been derived from the photosystem. These metabolisms already are completed in some evolved prokaryotes, for example the cyanobacteriumChlorogloea fritschii and aerobic photosynthetic bacteriaRhodospirillum rubrum andErythrobacter sp. Therefore, it can be reasonably presumed that the eukaryotic chloroplast and mitochondrion have once been formed as the result of metabolic (and genetic) differentiations in most evolved cyanobacterium. Symbiotic theory has explained the origin of eukaryotic cell as that in which the mitochondrion and chloroplast have been derived from endosymbionts of aerobic bacterium and cyanobacterium, respectively, and has mentioned as one of the most potent supportive evidences that amino acid sequences of the photosynthetic and O2 -respiratory enzymes show similarities to corresponding prokaryotic enzymes. However, as will be shown in this discussion, many examples have shown currently that prokaryotic sequences of informative molecules are conserved well not only in those of the mitochondrial and chloroplast molecules but also in the nuclear molecules. In fact, the similarities in sequence of informative molecules are preserved well among the organisms not only in phylogenetically close relationships but also under highly selective pressure, that is under a physiological constraint for the species in their habitats. Therefore, the similarities in amino acid sequences of proteins between the prokaryotes and the organelles are not necessarily direct evidence for their phylogenetical closeness: it gives still less evidence for a symbiotic relationship between the prokaryotes and the organelles. The metabolic compartmentalization of the membranes is an important tendency in cellular evolution to guarantee high specificity and rate of the metabolisms. It is suggested from the data that the intracellular membranes are not static but undergo dynamic turnover. Furthermore, these facts strongly support the Membrane Evolution Theory which was proposed by one of the authors in 1975.

Origin of eukaryota from Cyanobacterium: membrane evolution theory

It has been currently estimated that the life generated about four billion years ago in the primitive sea as a result of the chemical evolution. There is no doubt that, at that time, the protoorganism was a prokaryotic monad, formed from a certain aggregate of primitive proteins, nucleic acids, and other macromolecules and wrapped with (phospho)lipid membrane. Some workers have proposed that the macromolecules involved in the formation of the life were adsorbed on surface of clay particles in the primeval soup (Cairns-Smith 1982). However, it seems very unlikely that such a simple aggregation of the macromolecules would lead to the formation of a vital cell. The reasons for such uncertainty which have been discussed (see Nakamura 1987c) are: (1) The extant cells, without exception, are wrapped by a single membrane consisting of phospholipid bilayer. (2) Life is expressed only in a closed, rather than open, system isolated from the environment by the plasma membrane.

Is There an Alternative Path in Eukaryogenesis

The transition from prokaryotic to eukaryotic cells (‘Eukaryogenesis’) is still a biological mystery. The present paper revisits the question of the origin of the eukaryotic cell and suggests that the biochemical, ultrastructural aspects and the renewed efforts in space missions in Solar System exploration will present us with an opportunity for answering the question: Is there an alternative path in Eukaryogenesis?

Effects of amino acids on polysaccharide synthesis ofEscherichia coli K-12lon+ andlon− strains

Ultraviolet-sensitivelon− mutant ofEscherichia coli K-12 produced abundant polysaccharide when grown in a minimal medium at 37 C, but not when grown in a broth medium. The repression of polysaccharide synthesis in the broth-grownlon− andlon+ cells was studied. The effects were largely dependent on the amino acid concentrations and on the requirements of the strain used. At 200 μg per ml of each of the essential amino acids, histidine, proline, and threonine, there was complete inhibition of polysaccharide synthesis. At 200 μg per ml the required amino acids, tryptophane and tyrosine promoted polysaccharide synthesis. Most amino acids inhibited cell growth at 200 μg per ml but the inhibiting effect was smaller at 400 μg per ml. Polysaccharide synthesis of cells was not correlated with the growth rate, and occurred even under non-growing conditions.

Salt Sensitivity of Cells

The first life form, a proto-cell, is believed to have evolved in the primitive sea. The sea nurtured early life supplying both inorganic and organic materials. However, it is not clear whether all the minerals positively supported proto-cells, although the mineral elements required by present-day cells are abundant in seawater. Geological evidence suggests that sea water accumulated upon the cooling of dense vapor in the atmosphere which derived from active volcanoes on the primitive earth. Therefore, we can assume that very little or no sodium chloride was present in primitive seawater when the proto-cells evolved. However, it is a fact that seawater currently contains on average, 3.5% sodium chloride. The increase in the sodium chloride concentration likely resulted from:(i) extraction from the solid earth, which has been estimated to contain 460 sodium atoms per 10,000 atoms of silicon (Gymer, 1973). (ii) evaporation of water into the atmosphere. Water evaporation from the surface of lakes is known to increase the sodium chloride concentration. For example, the salt concentration reaches saturation (about 35% at 20°C) in some area of the Dead Sea and Great Salt Lake. However, halophilic bacteria and certain other organisms flourish in this type of salt water.

From Bacteria to Protista

Life can be defined as a material system that fills the following three conditions simultaneously; (i) it makes and maintains by itself the system that has a specific attribute to be termed so-called “life”, (ii) it should replicate and reproduce by itself descendants, and (iii) it can evolve with time. The first such organized system, proto-cell, appeared in primitive sea about four billion years ago. Proto-cells are Prokaryotic in cellular organization and belong to the bacterial world. A remarkable feature of prokaryotic cells is that the nucleoid area containing the genome is not surrounded by a nuclear membrane. In contrast, the genome in eukaryotic cells is located in a nucleus, (mitochondria and chloroplasts possess also DNAs), surrounded by generally two (an inner and outer) nuclear membranes.

Origin of the Proto-Cell Membrane

The unit of all living systems is the cell. Cells are surrounded by cell (or plasma) membranes which are constructed from phospholipid bilayer (abbreviated to lipid bilayer hereafter) as skeleton.

Membranous evolution of photosynthetic prokaryotes and non-symbiotic origin of eukaryotic cell

It has been estimated generally that the proto-cell originated about 3.8-4.0 billion years ago as a result of chemical evolution and eukaryotic cell(s) were generated about 1.5 billion years ago from prokaryote(s). So, it can be said roughly that the prokaryotic era had passed through a 2.3-2.5 billion years since origin of the proto-cell. The prokaryotic cells evolved various pathways of metabolisms and membranous organelles for this long time. The most significant pathways occurred are those for fermentation, photosynthesis and respiration. Photosynthetic bacterium Rhodospirillum rubrum can grow using metabolisms of fermentation, photosynthesis, and 02-respiration respectively according to the environment. These metabolisms had to have been accumulated as a result of adaptation to the environments encountered in the long history. Our laboratory has been interested in how membra~ nous differentiation compartmentalized the evolved metabolisms in the prokaryotic cells. We have found that R. rubrum cells contain a 50 kilo-base plasmid, which can be eliminated by treatment of a dye, acriflavine. The plasmid-less mutant has no longer ability of photosynthesis because it can not form the photosynthetic pigments and the membranous organelle, chromatophore. Therefore, it is evident that some genes cording for these are located on the plasmid DNA. In fact, when the mutant cells were transformed by the DNA, abilities to form the pigments and the chromatophore are regenerated. The result indicates clearly that R. rubrum cell possesses both photosynthetic and

Metabolic evolution and origin of eukaryotic cell-membrane evolution theory

Since the endosymbiotic theory was reproposed by L. Margulis in 1970, enormous amounts of knowledge have been accumulated in the field of molecular biology and cytology. Therefore, the time has come to rediscuss the theory on the basis of the current knowledge. The DNA content of a single cell increases rapidly with the evolution of organism through the world of prokaryote and eukaryote. Further, metabolic compartmentarization progresses together with the cellular evolution. In this situation, the intracellular membranes shoulder the weight of its responsibility. The complexity of the membrane system is an expression of cellular evolution through the biological world. Mycoplasma contains only plasma membranes as the membrane system, while complex invaginations and differentiations of the plasma membrane occur to form so-called mesosomes in bacteria, especially in gram-positives, and chromatophores in photosynthetic bacteria. The cyanobacteria have highly organized thylakoids, and they are arranged ~o make bundless and lattices under certain conditions. On the other hand, in eukaryotic cells, the membranous differentiation evolved to form double membrane organelles and single membrane organells. In mitochondrion and chloroplast, the inner membrane invaginates into the matrix and makes the specific membrane structures. However, the organellar morphogenesis depends largely upon the physiological and genetical conditions of the cell. In the origin of life, the newly born cell would contain few enzymes which were produced one by one through the chemical evolution. However, the metabolism increased complexity with the cellular evolution. It has been presumed currently that the primitive atmosphere on the earth was without 02 gas, and thus the organisms at that time produced energy for living by fermentation. The most widely distributed metabolism in the biological world is so-called EMP pathway. Furthermore, many types of the fermentative metabolisms contain a part of EMP pathway, from glyceroaldehyde-3-phosphate to pyruvate. Also, ATP-generating reactions are gathered in this system. The extant greenand purple-sulfur bacteria possess two main metabolisms for anaerobic photosynthesis; light harvesting system and Calvin cycle. The former can change light energy to chemical energy (ATP and NADH), and the latter can assimilate CO 2 by using ATP and NADH. As Calvin cycle is a reversion of the fermentative