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Biomedical subjects

T Takeuchi

Publications and source records attributed to T Takeuchi.

At least 1,729 records · Page 96Linked to original sources
PubMed1984

3,4-dihydroxystyrene, a novel microbial inhibitor for phenylalanine hydroxylase and other pteridine-dependent monooxygenases.

A new microbial inhibitor for rat-liver phenylalanine hydroxylase (L-phenylalanine, tetrahydropteridine: oxygen oxidoreductase (4-hydroxylating), EC 1.14.16.1) was isolated from a culture medium of Fomes tasmanicus, and its structure was determined as 3,4-dihydroxystyrene. This compound inhibited the enzyme by 50% at a concentration of 5 X 10(-6) M and 5 X 10(-7) M, respectively, without or with preincubation at 25 degrees C for 15 min. Without preincubation, dihydroxystyrene inhibited phenylalanine hydroxylase noncompetitively with phenylalanine and a pteridine cofactor, 6,7-dimethyltetrahydropterin, and uncompetitively with oxygen. A change in kinetic properties of the inhibition was observed when the enzyme was preincubated with dihydroxystyrene; the degree of inhibition was increased, and the purely noncompetitive-type inhibition with phenylalanine changed to a mixed-type inhibition. A study concerning the structure-inhibitory activity relationship using several compounds similar to dihydroxystyrene, indicated that the catechol structure is essential and that the structure of the aliphatic side-chain affects the inhibitory potency. A similar degree of inhibition was observed using 6,7-dimethyl- or 6-methyltetrahydropterin or tetrahydrobiopterin as a cofactor. Dihydroxystyrene also inhibited other pteridine-dependent monooxygenases, tyrosine hydroxylase (EC 1.14.16.2) and tryptophan hydroxylase (EC 1.14.16.4), indicating that dihydroxystyrene is a general inhibitor for pteridine-dependent monooxygenases.

Animals↗
PubMed1984

Action of the e locus of mice in the response of phaeomelanic hair follicles to alpha-melanocyte-stimulating hormone in vitro.

Dibutyryl adenosine 3',5'-monophosphate (dibutyryl cyclic AMP) induced eumelanin synthesis in hair bulb melanocytes of recessive yellow (e/e) mice in vitro, whereas alpha-melanocyte-stimulating hormone (alpha-MSH) did not. In contrast, the melanocytes of lethal yellow (Ay/a) mice produced eumelanin in response to both dibutyryl cyclic AMP and alpha-MSH. These results suggest that the e locus controls a mechanism that determines the function of an alpha-MSH receptor.

Animals↗
PubMed1984

Suppressor T cell function in patients with rheumatoid arthritis complicated by vasculitis.

Concanavalin A (Con A)-induced suppressor T cell activity was determined in 10 rheumatoid arthritis (RA) patients with vasculitis, 34 RA patients without vasculitis, and 10 healthy individuals. The percent Con A-induced suppression in RA patients with vasculitis was 24.6. In contrast, it was 68.4% in those RA patients without vascular lesions. Further, the proportion of T cells reactive with OKT8 monoclonal antibody was also decreased in RA patients with vasculitis. Accordingly, the reduced Con A-induced suppressor T cell activity in these RA patients resulted, in part, from the reduction in the number of cells of the suppressor T cell subset. Those patients with vascular lesions also had a higher percentage of positive antilymphocytotoxic antibodies than RA patients without vasculitis. Since the differences in Con A-induced suppressor T cell activity and frequency of positive antilymphocytotoxic antibodies were so great, we believe RA patients with vasculitis could be recognized as a disease group distinct from RA patients without vasculitis.

Adult↗
PubMed1984

Cellular mechanism of DNA-specific antibody synthesis by lymphocytes from systemic lupus erythematosus patients.

The cellular mechanism of anti-DNA antibody synthesis in patients with systemic lupus erythematosus (SLE) was studied by DNA-specific solid-phase radioimmunoassay. Anti-DNA antibody synthesis in response to DNA was T-dependent, and the experiments with reconstituted lymphocytes from identical twins discordant for SLE showed that B cells and T cells from SLE patients must cooperate to synthesize anti-DNA antibody. Anti-DNA antibody synthesis by lymphocytes from patients with inactive SLE was enhanced by T4 cells and suppressed by T8 cells in response to DNA. Although T4 cells from patients with active SLE could enhance anti-DNA antibody synthesis by autologous B cells, their T8 cells could not suppress anti-DNA antibody synthesis by autologous B cells. These results indicate that elevated anti-DNA antibody synthesis in response to DNA in patients with active SLE is due to abnormalities of both SLE B cells and SLE T cells. They further indicate that dysfunction of T8 cells from patients with active SLE may, in part, be responsible for deficient regulation of anti-DNA antibody synthesis.

Antibodies↗
PubMed1984

Serum and substratum-dependent coupled loss of differentiated and tumorigenic phenotypes in B16-conv melanoma cells.

Clonal B16 mouse melanoma conv cells are tumorigenic spindle-shaped cells (S-type cells) exhibiting tyrosinase activity and melanosomes under usual culture conditions. When the cells passaged on glass substratum were plated for colony formation on plastic substratum in Eagle's minimum essential medium (MEM) with 10% calf bovine serum, most of them converted to fibroblastlike cells (F-type cells) with the coupled loss of differentiated and tumorigenic phenotypes. However, they continued to be S-type cells provided that they were plated on glass substratum. The conversion from S- to F-type cell was not induced with high frequency even on plastic substratum when the concentration of calf serum in the medium was low (1-2%). These results indicate that both plastic substratum and serum factor are requisites for converting the phenotypic expression of the conv cells. Partial characterization of the serum factor indicates that it is adsorbable to plastic substratum, inactivated at 70 degrees C for 10 min, salted out at 40% of saturated ammonium sulfate; in addition the factor seems to act on cells within 1 day after plating.

Animals↗
PubMed1984

A great Brunner's gland adenoma of the duodenal bulb.

The occurrence of Brunner's gland adenoma in the duodenum is infrequent. The authors report a case of great Brunner's gland adenoma of the duodenal bulb, which is of interest because of its great size (8.5 X 4.5 cm) and the negative result of the endoscopic biopsy. Endoscopy has improved the diagnosis of the duodenal tumors; however, traditional endoscopic pinching biopsy does not always make a histological diagnosis. In our case, the endoscopic biopsy was negative because the tumor was located completely in the submucosa and the biopsy forceps was unable to reach to the tumor tissue.

Adenoma↗