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A Akutsu

Publications and source records attributed to A Akutsu.

11 recordsLinked to original sources
PubMed2000

Possible involvement of endothelium-derived hyperpolarizing factor (EDHF) in the depressor responses to platelet activating factor (PAF) in rats.

1. In anaesthetized rats, platelet activating factor (PAF; 1 microg kg(-1)) decreased mean arterial blood pressure by around 60 mmHg (n=18). This depressor response was completely blocked by the PAF antagonist, CV-6209 (1 mg kg(-1)), indicating the role of PAF-specific receptor in the response. 2. N(G)-nitro-L-arginine methyl ester (L-NAME; 50 mg kg(-1)), an NO synthase inhibitor, profoundly elevated systemic blood pressure (n=19), indicating an important role of NO in the basal blood pressure regulation. The depressor response to PAF (1 microg kg(-1)) normalized against that to sodium nitroprusside (SNP) (10 microg kg(-1)) was not substantially different between rats treated without and with L-NAME (n=4). In contrast, the depressor effect of acetylcholine (0.03 - 1.0 microg kg(-1)) normalized against that of SNP (10 microg kg(-1)) was significantly attenuated by L-NAME (n=5). 3. Charybdotoxin (0.4 mg kg(-1)) plus apamin (0.2 mg kg(-1)) significantly attenuated the depressor response to PAF (1 microg kg(-1)) (n=5) without affecting the blood pressure change due to SNP (1 mg kg(-1)) (n=3). Charybdotoxin (0.4 mg kg(-1)) (n=4) or apamin (0.2 mg kg(-1)) (n=4) alone did not affect the PAF-induced depressor response. 4. These findings suggest that EDHF may make a significant contribution to the depressor response to PAF in rats. Although NO plays the determinant role in the basal blood pressure regulation, its contribution to PAF-produced depressor response seems to be less as compared with that to the depressor response to acetylcholine.

Animals↗
PubMed1991

Identification of a unique specificity determinant of the colicin E3 immunity protein.

Plasmid immunity to a nuclease-type colicin is defined by the specific binding of an immunity (or inhibitor) protein, Imm, to the C-terminal nuclease domain, T2A, of the colicin molecule. Whereas most regions of colicin operons exhibit extensive sequence identity, the small plasmid region encoding T2A and Imm is exceptionally varied. Since immunity is essential for the survival of the potentially lethal colicin plasmid (Col), we inferred that T2A and Imm must have co-evolved, retaining their mutual binding specificities. To evaluate this co-evolution model for the col and imm genes of ColE3 and ColE6, we attempted to obtain a stabilized clone from a plasmid which had been destabilized with a non-cognate immunity gene. A hybrid Col, in which the immE3 gene of the ColE3 was replaced with immE6 from ColE6, was lethal to the host cells upon SOS induction. From among this suicidal cell population, we isolated a stabilized, i.e., evolved, clone which produced colicin E3 (E3) stably and exhibited immunity to E3. This change arose from only a single mutation in ImmE6, from Trp48 to Cys, the same residue as in the ImmE3 sequence. In addition, we constructed a series of chimeric genes through homologous recombination between immE3 and immE6. Characterization of these chimeric immunity genes confirmed the above finding that colicins E3 and E6 are mostly distinguished by only Cys48 of the ImmE3 protein.

Amino Acid Sequence↗
PubMed1989

Molecular structure and immunity specificity of colicin E6, an evolutionary intermediate between E-group colicins and cloacin DF13.

The primary structure of a 3.1-kilobase E6 or E3 segment carrying colicin and related genes was determined. Plasmid ColE6-CT14 showed striking homology to ColE3-CA38 throughout this segment, including homology to the secondary immunity gene, immE8, downstream of the E6 or E3 immunity gene. The ColE3-CA38 and ColE6-CT14 sequences, however, contained an exceptional hot spot region encoding both the colicin-active domain (RNase region) and the immunity protein, reflecting their different immunity specificities. On the other hand, some chimeric plasmids were constructed through homologous recombination between colicin E3 and cloacin DF13 operons. The resulting plasmids were deduced to produce chimeric colicins with a colicin E3-type N-terminal part, a cloacin DF13-type C-terminal-active domain, and the DF13 immunity protein. The killing spectra of the chimeric colicins and the immunities of the plasmids were identical to those of colicin E6 and ColE6-CT14, respectively, showing that the colicin E6 immunity specificity is completely equivalent to that of cloacin DF13. Nevertheless, colicin E6 has been found to show a sequence diversity from cloacin DF13 almost to the same extent as that from colicin E3 in their RNase and immunity regions, indicating that only a small number of amino acids defines the immunity specificity for discrimination between colicins E3 and E6 (or cloacin DF13).

Amino Acid Sequence↗