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Biomedical subjects

H Takeshima

Publications and source records attributed to H Takeshima.

244 records · Page 14Linked to original sources
PubMed1973

Screening and isolation of penicillinase inhibitor, KA-107.

It is known that penicillin resistance of bacteria is mainly caused by the inactivation of penicillin by penicillinase derived from such strains. We have developed a screening procedure for penicillinase inhibitors. Several microorganisms were found to produce such inhibitors, and from the culture filtrate of Streptomyces gedanensis ATCC 4880 a penicillinase inhibitor, named KA-107, was isolated. The characteristics of this inhibitor were revealed by an in vitro test by using penicillinase derived from penicillin resistant Staphylococcus aureus, FS-1277. When KA-107 was used in combination with penicillin-G, ampicillin, d- or l-phenethicillin, the growth inhibitory activity of these penicillins was maintained.

Anti-Bacterial Agents↗
PubMedDate not supplied

Existence of distinct sodium channel messenger RNAs in rat brain.

The sodium channel is a voltage-gated ionic channel essential for the generation of action potentials. It has been reported that the sodium channels purified from the electric organ of Electrophorus electricus (electric eel) and from chick cardiac muscle consist of a single polypeptide of relative molecular mass (Mr) approximately 260,000 (260K), whereas those purified from rat brain and skeletal muscle contain, in addition to the large polypeptide, two or three smaller polypeptides of Mr 37-45K. Recently, we have elucidated the primary structure of the Electrophorus sodium channel by cloning and sequencing the DNA complementary to its messenger RNA. Despite the apparent homogeneity of the purified sodium channel preparations, several types of tetrodotoxin (or saxitoxin) binding sites or sodium currents have been observed in many excitable membranes. The occurrence of distinguishable populations of sodium channels may be attributable to different states of the same channel protein or to distinct channel proteins. We have now isolated complementary DNA clones derived from two distinct rat brain mRNAs encoding sodium channel large polypeptides and present here the complete amino-acid sequences of the two polypeptides (designated sodium channels I and II), as deduced from the cDNA sequences. A partial DNA sequence complementary to a third homologous mRNA from rat brain has also been cloned.

Amino Acid Sequence↗
PubMedDate not supplied

Expression of functional sodium channels from cloned cDNA.

The voltage-gated sodium channel is a transmembrane protein essential for the generation of action potentials in excitable cells. It has been reported that sodium channels purified from the electric organ of the electric eel, Electrophorus electricus, and from chick cardiac muscle consist of a single polypeptide of relative molecular mass (Mr) approximately 260,000, whereas those purified from rat brain and from rat and rabbit skeletal muscle contain, in addition to the large polypeptide, one or two smaller polypeptides of Mr 33,000-43,000. The primary structures of the Electrophorus sodium channel and two distinct sodium channel large polypeptides (designated as sodium channels I and II) from rat brain have been elucidated by cloning and sequencing the complementary DNAs. The purified sodium channel preparations from Electrophorus electroplax and from mammalian muscle and brain, when reconstituted into lipid vesicles or planar lipid bilayers, exhibit some functional activities. The successful reconstitution with the Electrophorus preparation would imply that the large polypeptide alone is sufficient to form functional sodium channels. However, studies with the rat brain preparation suggest that the smaller polypeptide of Mr 36,000 is also required for the integrity of the saxitoxin (STX) or tetrodotoxin (TTX) binding site of the sodium channel. Here we report that the messenger RNAs generated by transcription of the cloned cDNAs encoding the rat brain sodium channel large polypeptides, when injected into Xenopus oocytes, can direct the formation of functional sodium channels.

Animals↗
PubMedDate not supplied

Primary structure of the receptor for calcium channel blockers from skeletal muscle.

The complete amino-acid sequence of the receptor for dihydropyridine calcium channel blockers from rabbit skeletal muscle is predicted by cloning and sequence analysis of DNA complementary to its messenger RNA. Structural and sequence similarities to the voltage-dependent sodium channel suggest that in the transverse tubule membrane of skeletal muscle the dihydropyridine receptor may act both as voltage sensor in excitation-contraction coupling and as a calcium channel.

Amino Acid Sequence↗
PubMedDate not supplied

Biological role of thymidine phosphorylase in human astrocytic tumors.

Thymidine phosphorylase (TP) has strong angiogenic activity and is overexpressed in a wide variety of malignant tumors. To elucidate the role of TP in human astrocytic tumors, we immunohistochemically investigated the expression of TP in 62 astrocytic tumors (12 astrocytomas, 12 anaplastic astrocytomas and 38 glioblastomas). Fifty-five astrocytic tumors (88.7%) were immunopositive for TP. The level of TP-expression was significantly correlated with the malignancy grade of astrocytic tumors; most of malignant gliomas highly expressed TP, while a small number of cells were positive in low grade astrocytomas (p < 0.001). Using double-immunostaining, we clarified that TP-expression was predominantly detectable in macrophages. There was no significant correlation between MIB-1 labeling index and TP-expression. However, TP-expression and the microvessel density were well correlated. These suggest that TP, mainly produced by the infiltrated macrophages, may play an important role in the progression of astrocytic tumors via neovascularization. Inhibitor of TP may represent a therapeutic modality for treating malignant gliomas.

Antigens, CD↗