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Biomedical subjects

Y Sakamoto

Publications and source records attributed to Y Sakamoto.

At least 685 records · Page 38Linked to original sources
PubMed1983

Factors affecting the cold inactivation of an acetyl-coenzyme-A hydrolase purified from the supernatant fraction of rat liver.

An extramitochondrial acetyl-coenzyme-A hydrolase from rat liver is shown to be a cold-labile oligomeric enzyme that undergoes a reversible conformational transition between a dimeric and a tetrameric form in the presence of adenosine 5'-triphosphate or adenosine 5'-diphosphate at 25-37 degrees C, and between a dimeric and a monomeric form at low temperature. The enzymatically active dimer is fairly stable at 25-37 degrees C, but much less stable at low temperature, dissociating into monomer with no activity. At 37 degrees C and low concentrations of enzyme protein (less than or equal to 14 micrograms/ml), the activity decreased rapidly and only 10% of the initial activity remaining after 60 min. Addition of bovine serum albumin or immunoglobulin G to the medium completely prevented inactivation of the dimeric enzyme at low concentration at 37 degrees C, but had little effect on cold inactivation of the enzyme. Cold inactivation of the dimeric enzyme was partially prevented by the presence of various CoA derivatives. The order of potency was acetyl-CoA (substrate) greater than or equal to butyryl-CoA greater than octanoyl-CoA greater than CoA (product) greater than acetoacetyl-CoA. Another enzyme product, acetate, had little effect on cold inactivation. Polyols, such as sucrose, glycerol, and ethylene glycol, and high concentrations of NaCl, KCl, pyrophosphate and phosphate also greatly prevented cold inactivation. Cold inactivation was scarcely affected by pH within the pH range at which the enzyme was stable at 37 degrees C.

Acetyl-CoA Hydrolase↗
PubMed1983

Screening for carcinogens by DNA-synthesis inhibition test using mouse L-cells.

Bacterial test systems for potential carcinogens sometimes give false negative results. To overcome this problem, several short term test systems have been described. One of them is the DNA-synthesis inhibition test described by Painter (1977). Our DNA-synthesis inhibition test system using mouse L-cells gave positive results when monocrothaline, phenacetin and thioacetamide, which were negative in the Ames test, were tested.

Animals↗
PubMed1983

Purification of insulin receptor with full binding activity.

Insulin receptor was purified 2400-fold with an overall yield of 40% from human placental membranes by affinity chromatography on wheat germ agglutinin-Sepharose and insulin-Sepharose. The receptor was eluted from insulin-Sepharose using mild conditions, eliminating urea, so that it was stable and retained full insulin-binding activity. Chromatofocusing and gel filtration analysis indicated that the receptor preparation was apparently pure. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed three high molecular weight protein bands with Mr = 320,000, 300,000, and 270,000 under nonreducing conditions and two major protein bands with Mr = 135,000 and 90,000 under reducing conditions. The purified receptor showed a curvilinear Scatchard plot with maximum insulin binding of 28.5 micrograms per mg of protein. In comparison, the receptor eluted from insulin-Sepharose with previously used conditions in the presence of urea resulted in maximum insulin binding of only 6 micrograms per mg of protein. This indicates that a 4-to 5-fold increase in specific activity can be obtained by using the new elution conditions.

Chromatography, Affinity↗
PubMed1983

Effects of nucleotides on a cold labile acetyl-CoA hydrolase from the supernatant fraction of rat liver.

An acetyl-CoA hydrolase that is labile at low temperature was purified to homogeneity from the supernatant fraction of rat liver. The monomeric molecule, estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, had a molecular weight of about 63 000, while that of the purified enzyme, estimated by gel filtration, was 135 000. Thus, the enzyme consists of two subunits of identical molecular weight. On addition of adenosine 5'-triphosphate (ATP) or adenosine 5'-diphosphate (ADP) at 25 degrees C, the dimeric form of the enzyme aggregated to tetrameric forms (Mr 242 000 and Mr 230 000, respectively), whereas addition of adenosine 5'-monophosphate had little effect on enzyme association (Mr 145 000). When ATP was removed from the ATP-treated tetrameric enzyme by dialysis, the tetramer was mostly dissociated into the dimeric form. The apparent Km values for acetyl coenzyme A of the dimeric enzyme and tetrameric enzyme, reconstituted from the former in the presence of 2 mM ATP, were 170 microM and 60 microM, respectively. The purified dimeric enzyme was inactivated by exposure to lower temperature, especially below 10 degrees C. The various nucleotides tested partially stabilize the dimeric enzyme at low temperature, ATP being the most effective. Sucrose density gradient centrifugation showed that loss of catalytic activity by cold treatment was accompanied by dissociation of the dimer and tetramer into protomer.

Acetyl-CoA Hydrolase↗
PubMed1983

Organ-specific difference in the sugar chains of gamma-glutamyltranspeptidase.

Sugar chains of gamma-glutamyltranspeptidase purified from neonatal mouse liver and adult mouse kidney were quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. A comparative study of the structures of the oligosaccharides has revealed that the GlcNAc beta 1 leads to 4Man beta 1 leads to group is found in the sugar chains of kidney enzyme but not in those of liver enzyme. This is considered as an organ-specific difference common to mammals because the same phenomenon was found in bovine and rat enzymes.

Acyltransferases↗
PubMed1983

Purification and properties of bovine liver gamma-glutamyltransferase.

gamma-Glutamyltransferase [EC 2.3.2.2] (gamma-GTP) was purified to a homogeneous state from bovine liver. It had an apparent molecular weight of about 110,000, as judged by polyacrylamide gel electrophoresis, and consisted of two non-identical glycopeptides with molecular weights of 68,000 and 27,000. The amino acid composition of the bovine liver enzyme was similar to those of other gamma-GTPs. The enzyme contained large amounts of neutral sugars, amino sugars and sialic acid, although the sialic acid content varied in different preparations. The Michaelis constant of the enzyme was estimated to be 0.8 mM for gamma-L-glutamyl-p-nitroanilide in the presence of glycylglycine and 1.25 mM in the absence of glycylglycine. Glutathione competitively inhibited the release of p-nitroaniline from gamma-L-glutamyl-p-nitroanilide with a Ki value of 0.3 mM. The specific activities of the enzyme for gamma-L-glutamyl-p-nitroanilide in the presence of glycylglycine (pH 8.6) and for glutathione, a natural substrate (pH 7.4), were comparable to those reported for gamma-GTPs from other mammalian sources. The bovine liver enzyme showed the same gamma-glutamyl group acceptor specificity as other gamma-GTPs from normal mammalian tissues. The phosphate-independent glutaminase activity of the enzyme was much lower than that of the rat kidney enzyme both in the presence and absence of maleate.

Amino Acids↗
PubMed1983

IgG4 antibodies in patients with house-dust-mite-sensitive bronchial asthma: relationship with antigen-specific immunotherapy.

Sera from 40 patients with house-dust-mite (Dermatophagoides farinae)-sensitive bronchial asthma were evaluated by solid-phase radioimmunoassay for their mite-specific IgG4 antibody levels. Asthmatic patients undergoing specific immunotherapy possessed a significantly higher mean value of IgG4 antibodies than normal controls and asthmatics without immunotherapy (p less than 0.01 and p less than 0.05, respectively). Moreover, evaluation of 11 patients before and after immunotherapy showed that IgG4 antibodies tend to increase during immunotherapy. The clinical significance of the IgG4 subclass as blocking antibodies in immediate allergic reactions is also briefly discussed.

Animals↗
PubMed1983

Alteration in the inducibility by dexamethasone of the activity of tyrosine aminotransferase and tryptophan oxygenase in regenerating rat liver after partial hepatectomy.

In adrenalectomized rats, the activity of tryptophan oxygenase in liver cytosol was increased 4 h after dexamethasone injection, with a peak on day 2. It then gradually decreased to the value obtained in normal animals treated with dexamethasone. In adrenalectomized, 70% hepatectomized rats, tryptophan oxygenase activity decreased significantly during the period of DNA synthesis after partial hepatectomy; it then increased to above the level existing before hepatectomy, reaching a maximum on day 5, and subsequently returned to the level before hepatectomy. These changes were well correlated with those of dexamethasone receptors at all times after adrenalectomy and partial hepatectomy. In adrenalectomized rats, tyrosine aminotransferase activity was increased 4 h after dexamethasone injection, reached a maximum on day 2, and then remained elevated. The level was increased by subsequent 70% hepatectomy, reached a maximum on day 5, and then began to decrease, but activity was still high on day 10 after hepatectomy when the receptor level had returned to the value existing before hepatectomy. When actinomycin D or cycloheximide was injected with dexamethasone, the induction of the two enzymes was completely inhibited. The activities of the two enzymes in regenerating liver of rats without adrenals and without glucocorticoid treatment were as low as those in adrenalectomized rats without glucocorticoid treatment. Thus, there was a good correlation between the dexamethasone receptor level and the induction of tryptophan oxygenase, but there was a dissociation between the receptor level and the induction of tyrosine aminotransferase after adrenalectomy and partial hepatectomy. The mechanism of this dissociation is unknown.

Adrenalectomy↗
PubMed1983

Limb deformity induced in chick embryo by hydroxyurea.

After a dose of 800 micrograms of hydroxyurea (HU) was administered to day-4 chick embryos in ovo, the limb deformity including micromelia was observed. We examined the teratogenic mechanism of the action for HU by using histochemical and biochemical techniques. The present study provides histological evidence for the cell death and the depression of cell proliferation just after the treatment with HU and the retardation in periosteal ossification during the process of repair and/or recovery from cell death. On the other hand, the incorporation of [3H]glucosamine and [35S]sulfate into glycosaminoglycan was inhibited at day-7 and day-9, when the embryos are in the process of repair and/or recovery. The cartilage specific proteoglycan, an index of chondrogenesis, appeared at day-7, but the ratio of cartilagenous proteoglycan/noncartilagenous proteoglycan in the treated limbs was depressed. These results suggest that the slight retardation in chondrogenesis and/or the incomplete function of chondrocyte were induced by the treatment with HU in chick embryos. It is considered from above observation that the retardation in chondrogenesis and osteogenesis caused during the repair and/or recovery process of cell death brought about the limb deformity; shortening, thinning and bending of hind limbs.

Animals↗
PubMed1983

A case of pituitary gigantism who had two episodes of diabetic ketoacidosis followed by complete recovery of diabetes.

A 17-year-old boy with pituitary gigantism who had two episodes of diabetic ketoacidosis is reported. Glucose tolerance and insulin secretion were evaluated before, during and after each episode of ketoacidosis. The patient was 201 cm tall and weighed 137 kg. Before surgery, his plasma growth hormone level was 3,000 ng/ml, glucose tolerance was almost normal and insulin response to glucose load was enhanced. He fell into diabetic ketoacidosis twice; 3 weeks after hypophysectomy and one year later after getting the "flu". On each occasion, insulin treatment was needed only temporarily. After the ketoacidosis improved, glucose tolerance and C-peptide responses became nearly normal. Urine C-peptide was low during and immediately after the second episode, but increased to normal following recovery. It is presumed that a pre-operative compensation for the diabetogenic action of excess growth hormone by hyper-secretion of insulin was broken when superimposed stress was added. This is an example in which subnormal insulin response may not be a prerequisite for the occurrence of a severe diabetic state, and decompensated insulin secretion leading to ketoacidosis may not imply permanent damage to the beta cells.

Adolescent↗
PubMed1983

Clinical study of cardiac arrhythmias using a 24-hour continuous electrocardiographic recorder (5th report)--antiarrhythmic action of coenzyme Q10 in diabetics.

An investigation was undertaken to evaluate the antiarrhythmic effect of CoQ10 on VPBs using the Holter ECG, in 27 patients with no clinical findings of organic cardiopathies. As a result, the effect of CoQ10 on VPBs was considered beneficial in 6 (22%) of 27 cases, consisting of 1 patient with hypertension and 5 patients with DM. Even in the remaining 2 patients with DM, the frequency of VPBs was reduced by 50% or more during treatment with CoQ10. The mean reduction of VPBs frequency in the 5 responders plus these 2 patients with DM was 85.7%. These findings suggest that CoQ10 exhibits an effective antiarrhythmic action not merely on organic heart disease but also on VPBs supervening on DM.

Adult↗