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Biomedical subjects

I Tabushi

Publications and source records attributed to I Tabushi.

11 recordsLinked to original sources
PubMed1988

Allosteric behavior of artificial compounds.

The artificial allosteric molecules were prepared by connecting two independent metal porphyrin molecules by covalent bond. These molecules as fragments behave very similarly to the monomeric metal porphyrins except adsorption dissociation characteristics. In this paper we would like to discuss mostly on interesting and useful cooperativity or cooperative binding dissociation of small molecules like CO, O2, or base to both of porphyrin metals. The original structure of the dimeric porphyrin, especially when they are very strongly cooperative, usually needs chemical strain between two porphyrin rings and this strain is released by the first binding of small molecule which causes coordinating change of the metal porphyrin.

Allosteric Regulation↗
PubMed1987

Circular dichroism study of bacteriorhodopsin-lipid interaction.

Delipidated bacteriorhodopsin purified from purple membrane of H. halobium was reconstituted with the circular dichroism active phospholipid. The observed circular dichroism spectra in the 450-700 nm region characteristic of bacteriorhodopsin showed the temperature dependence characterized by a midpoint at ca. 45 degrees C and this spectral change showed the disaggregation of bacteriorhodopsin trimer to monomer. The circular dichroism spectra in the 250-400 nm region characteristic of the azo chromophore of phospholipid exhibited a remarkable temperature dependence synchronized with the disaggregation of bacteriorhodopsin, suggesting that a large proportion of the phospholipid is present as boundary lipid.

Bacteriorhodopsins↗
PubMed1983

Kinetic study on the successive four-step reduction of Cyt c3.

A detailed kinetic study on the successive four-step reduction of cyt c3, which has four heme units in a single protein, III4 leads to III3II leads to III2II2 leads to III II3 leads to II4, was carried out by stopped-flow electronic spectroscopy (SF-UV) and stopped-flow circular dichroism spectroscopy (SF-CD). Based on the absorbance change vs. time and the ellipticity change vs. time at the characteristic CD, together with the electronic absorption of the enzyme, rate constants for the successive four electron transfer steps, k1-k4, were successfully estimated by computer simulation. The rate constants of the four steps (k1 = 19.8 s-1, k2 = 11.9 s-1, k3 = 8.9 s-1, and k4 = 1.6 s-1; 8.0 10(-4) M Na2S2O4) are quite different from the statistical values (4: 3: 2: 1), thus excluding the possibility of random reduction of hemes of equal reactivities. Instead, each heme has its own reactivity, probably dependent on its local environment. The value of k3 is somewhat higher than the statistical value, indicating the existence of an autoacceleration effect, although small. This autoacceleration is most probably due to a unique heme-heme and/or heme-environment interaction since unusual CD and electronic absorptions were observed at 350-400 nm at about the time corresponding.

Animals↗
PubMed1982

Specific recognition of pyrophosphate in nucleotides.

The lipophilic diammonium cation 1 was demonstrated to be a reagent to discriminate the number of the phosphate in nucleotides. Thus the highly hydrophilic nucleotides were selectively extracted into an organic phase by the formation of ion-pairs and selectively transported through a membrane by a carrier mechanism. The compound was also shown to be an efficient phase transfer reagent which activated the phosphate anion of AMP to give a facile synthesis of pyrophosphate linkages, ADP and ATP, without any protection of the sugar moiety.

Adenine Nucleotides↗
PubMed1981

Hydrolysis of ATP in chemical models.

Hydrolysis of ATP was found to be accelerated by the addition of hexadecyltrimethylammonium chloride (CTAC). The high acceleration was observed in the concentration below rather than above the critical micell concentration of CTAC. The catalytic effect was observed at pH's 5 and 8, while not significantly at pH 3.

Adenosine↗
PubMed1979

Molecular recognition of nucleotides by means of ionic interaction in hydrophobic media.

Adenosine phosphates, AMP, ADP and ATP were found to be recognized and extracted from aqueous to an organic phase by the newly prepared lipophilic diammonium salt, N,N'-distearyldiammonium dichloride of 1,4-diazabicyclo [2.2.2] octane 1. ADP and ATP were specifically bound by 1 under the condition of no appreciable binding of AMP. The conventional phase transfer reagent, trioctylmethylammonium chloride 2 was far less effective and lacked selectivity fort the binding of adenosine phosphates. This diammonium salt was used as a specific carrier of ADP in the passive transport through a liquid membrane. A high selectivity was observed in the transport rate of ADP relative to that of AMP.

Adenosine Diphosphate↗