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Biomedical subjects

Y Iitaka

Publications and source records attributed to Y Iitaka.

At least 55 records · Page 3Linked to original sources
PubMed1985

Interactions of Streptomyces subtilisin inhibitor with Streptomyces griseus proteases A and B. Enzyme kinetic and computer simulation studies.

Streptomyces subtilisin inhibitor (SSI), a dimeric protein that strongly inhibits subtilisins, was shown to form tight inhibitory complexes with Streptomyces griseus proteases A and B (SGPA and SGPB). The apparent dissociation constants of the SGPA-SSI and SGPB-SSI complexes were found to be orders of magnitude less than those of subtilisin-SSI complexes. Using the known atomic coordinates for SGPA and SSI, the highly complementary nature of the surface geometries of the two proteins was confirmed by a computer graphics study, which led to a proposed structure for the SGPA-SSI complex. Kinetic studies further suggested that the SSI dimer can bind two molecules of either SGPA or SGPB, and the 2:1-complexes (consisting of one inhibitor dimer and one enzyme molecule) apparently possess lower intrinsic dissociation constants than the 2:2-complexes. It was also shown that both of SGPA and SGPB are inhibited by both soybean trypsin inhibitor (Kunitz) and bovine pancreatic trypsin inhibitor (Kunitz), but far less strongly than by SSI.

Aspartic Acid Endopeptidases↗
PubMed1984

Crystal structure at 2.6 A resolution of the complex of subtilisin BPN' with streptomyces subtilisin inhibitor.

The crystal structure of the complex of a bacterial alkaline serine proteinase, subtilisin BPN', with its proteinaceous inhibitor SSI (Streptomyces subtilisin inhibitor) was solved at 2.6 A resolution. Compared with other similar complexes involving serine proteinases of the trypsin family, the present structure is unique in several respects. (1) In addition to the usual antiparallel beta-sheet involving the P1, P2 and P3 residues of the inhibitor, the P4, P5 and P6 residues form an antiparallel beta-sheet with a previously unnoticed chain segment (residues 102 through 104, which was named the S4-6 site) of subtilisin BPN'. (2) The S4-6 site does not exist in serine proteinases of the trypsin family, whether of mammalian or microbial origin. (3) Global induced-fit movement seems to occur on SSI: a channel-like structure in SSI where hydrophobic side-chains are sandwiched between two lobes becomes about 2 A wider upon complexing with subtilisin. (4) The complex is most probably a Michaelis complex, as in most of the other complexes. (5) The main role of the "secondary contact region" of SSI seems to be to support the reactive site loop ("primary contact region"). Steric homology of the two contact regions between the inhibitors of the SSI family and the pancreatic secretory trypsin inhibitor-ovomucoid inhibitor family is so high that it seems to indicate divergent evolutionary processes and to support the general notion as to the relationship of prokaryotic and eukaryotic genes put forward by Doolittle (1978).

Amino Acid Sequence↗
PubMed1983

Preliminary chemical and X-ray studies on the interactions of E. coli DNA with putrescine.

The interactions of putrescine, the major diamine in E. coli, with E. coli DNA as a model of phage DNA were studied by melting temperature analysis, equilibrium dialysis and X-ray diffraction with the aid of molecular model building. The chemical analysis of the DNA-putrescine complex shows that the molar binding ratio of putrescine to DNA (phosphate) is nearly 1 to 2. The equilibrium (or reversible) binding of putrescine to DNA was suggested by the fact that the melting temperature increased according to the concentration of added putrescine, and its elevation was not saturated even at the molar ratio of 6 to 1. The equilibrium dialysis experiments indicate that the association constant for the complex is a little smaller than, but in the same order (10(3) liter/mol) as, that of DNA-spermine complex. The binding of putrescine stabilizes the B-form of DNA fiber, which is well preserved even at 66% relative humidity. The distance between the neighboring DNA helices in the wet fiber increased with the increasing degree of hydration, as in the case of native DNA. Unlike spermine, putrescine does not form precipitate upon mixing with DNA in the concentration range for UV measurement, suggesting that the cross-bridge formed by putrescine is intra-double helical. The equilibrium binding of putrescine to DNA, seems to be important for the life cycle of lambda-phage.

Chemical Phenomena↗
PubMed1982

Depside as potent inhibitor of prostaglandin biosynthesis: a new active site model for fatty acid cyclooxygenase.

Forty depsides and depsidones, the esters of phenolcarboxylic acids, were examined for their inhibitory effect against prostaglandin biosynthesis with rabbit renal microsomes. 4-0-Methylcryptochlorophaeic acid was the most active inhibitor so far tested and its IC50 value was 0.34 muM. Kinetic investigation has shown that this depside acts competitively with respect to arachidonic acid as most of the non - steroidal antiinflammatory drugs. X-Ray analysis has revealed that 4-0-methylcryptochlorophaeic acid maintains its rigid conformation by forming a strong hydrogen bond between the hydroxyl and methoxyl groups. Comparison of CPK models between 4-0-methylcryptochlorophaeic acid and non-steroidal antiinflammatory drugs revealed that the carboxyl group and the two rings of these drugs are almost superimposable to those of the depside. This finding led us to propose a new active site model based on the three dimentional structure of the depside.

Animals↗