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Biomedical subjects

K Murakami

Publications and source records attributed to K Murakami.

At least 1,243 records · Page 69Linked to original sources
PubMed1980

Role of cations in the regulation of baker's yeast AMP deaminase.

The effect of polyamines and divalent cations including alkaline earth metals and transition metals on the AMP deaminase (AMP aminohydrolase EC 3.5.4.6) purified from baker's yeast was investigated. (1) Polyamines and alkaline earth metals activated the enzyme in the absence of ATP: these cations largely enhanced the maximal velocity without alteration of S0.5 and nH (Hill coefficient) values. However, transition metals acted as potent inhibitors, which decreased the maximal velocity of the enzyme in the absence of ATP. (2) All of the divalent cations showed an activation of the enzyme in the presence of ATP, followed by a progressive decrease in activity as the concentrations of transition metals increased. (3) The increase in the concentrations of polyamines or alkaline earth metals showed no more activating effect when the enzyme was fully activated by the addition of excess alkali metals in the absence of ATP, but divalent cation-activation was observed in the presence of ATP even if alkali metals were saturating. These results suggest the presence of two types of binding sites for cations: 1, the sites for free cations and 2, those for ATP-metal complexes. The former sites include the activating sites for alkali metals, polyamines and free alkaline earth metals, and the inhibitory sites for free transition metals. The latter sites are the activating sites for ATP-metal complexes, which are suggested to be commonly occupied by alkaline earth metals and transition metals and to form an ATP bridge (E-ATP-M) complex.

AMP Deaminase↗
PubMed1980

Effect of human leukocyte interferon on the metastatic lung tumor of osteosarcoma: case reports.

Three patients with pulmonary metastases of osteosarcoma underwent treatment with intravenous or intramuscular administration of human leukocyte interferon. In 2 cases, the size of the metastasized tumor mass diminished temporarily six or eight months after interferon treatment, and serum alkaline phosphatase levels decreased to normal. In 1 case, the tumor cell from the pleural exudate 1 could be isolated and cultivated in vitro. When 2,000 IU of interferon was added to the tumor cell culture, marked inhibition of tumor cell growth resulted. In the other case, interferon had no effect on the metastasized lung tumor.

Adolescent↗
PubMed1980

Human renal renin. Complete purification and characterization.

Complete purification of human renin from noncancerous, autopsied kidneys is reported. A 480,000-fold purification was achieved to yield renin with a specific activity of 950 Goldblatt units/mg. This preparation satisfied multiple criteria of purity as tested by polyacrylamide gel electrophoresis, isoelectric focusing, specific activity, analytical ultracentrifugation, and immunodouble diffusion. The molecular weight of the pure enzyme determined by sedimentation equilibrium is 40,000. The apparent molecular weight estimated by gel filtration is 41,000. The enzyme has an isoelectric point of pH 5.7. Human renin shows an affinity for concanavalin A, suggesting the presence of carbohydrates. These properties and the amino acid composition of human renin are different from those of renin obtained from other mammalian species. Human renin antibodies prepared with the pure enzyme preparation showed negligible cross-reactivity with renin from other mammalian species. The activity with homologous human renin substrate has a pH optimum of 6, whereas with substrates from other mammalian species the optima were in higher or lower pH ranges.

Amino Acids↗
PubMed1980

[The maintenance of insulin secretory response of long-term cultured pancreatic islets to glucose, acetylcholine and epinephrine (author's transl)].

The present study was performed to investigate whether long-term cultured rat pancreatic islets possess a postcultural insulin secretory response to hormones and neurotransmitters in spite of their lack of stimulation during the culture period. We also investigated the method of maintaining the insulin secretory response of islets cultured in a physiological concentration of glucose. The tissue culture media were TCM 199 supplemented with 5.5 mM glucose (A medium), 5.5 mM glucose plus 1 mM adenosine (B medium), 16.7 mM glucose (C medium), and 16.7 mM glucose plus 1 mM adenosine (D medium). Short-term incubation after the culture period of 14 days showed that the islets cultured in B, C and D media maintained the same insulin secretory responsiveness to 8.3 mM glucose and/or 5 microM acetylcholine and also to 1 microM epinephrine as did non-cultured islets. A similar response was found among the islets maintained in B, C and D media. An insulin secretory response to epinephrine and phentolamine was deficient in islets cultured in A medium, whereas it was maintained in those cultured in C medium. The responsiveness of the islets cultured in C medium to the concomitant stimulation by epinephrine and phentolamine was not different from that of the non-cultured islets. It was thus concluded that the addition of adenosine in the culture medium containing the physiological concentration of glucose was as effective in amintaining the insulin secretory ability of the islets as was the culture medium containing a high concentration of glucose, and it was suggested that even the pancreatic islets cultured in these media, though separated from the innervation might preserve acetylcholine and adrenergic receptors similar to freshly isolated islets. Considering the action of adenosine, the necessity of enhancing ATP and C-AMP concentrations in B cells was also suggested in order to maintain the insulin secretory ability of cultured pancreatic islets.

Acetylcholine↗
PubMed1980

Adenine nucleotide metabolism in Azotobacter vinelandii. Two metabolic pathways of AMP degradation.

AMP-degrading pathways in Azotobacter vinelandii cells were investigated. AMP nucleosidase (EC 3.2.2.4) was rapidly synthesized and reached a maximum at 24 h, while the activity of 5'-nucleotidase (EC 3.1.3.5) specific for AMP, which was negligible during the logarithmic phase of the growth, first appeared in 24 h-cultures, and reached a maximum after complete exhaustion of sucrose from the growth medium (70 h). Cell-free extracts of A. vinelandii of 48 h-cultures hydrolyzed AMP to ribose 5-phosphate and adenine in the presence of ATP, and adenine was deaminated to hypoxanthine. When ATP was excluded, AMP was dephosphorylated to adenosine, which was further metabolized to inosine, and finally to hypoxanthine. Hypoxanthine thus formed was reutilized for the salvage synthesis of IMP under the conditions where 5-phosphoribosyl 1-pyrophosphate was able to be supplied. These results suggest that the levels of ATP can determine the rate of AMP degradation by the AMP nucleosidase- and 5-'nucleotidase-pathways. The role of ATP in the AMP degradation was discussed in relation to the regulatory properties of AMP nucleosidase, inosine nucleosidase (EC. 3.2.2.2) and adenosine deaminase (EC 3.5.4.4).

Adenine Nucleotides↗
PubMed1980

Ion-dependent activation of AMP nucleosidase from Azotobacter vinelandii.

The effect of divalent cations on the purified AMP nucleosidase (AMP phosphoribohydrolase, EC 3.2.2.4) from Azotobacter vinelandii was investigated. All alkaline earth metal-ATP complexes were essential activators of the enzyme, and free alkaline earths also activated the enzyme in an allosteric manner: the apparent Ka for ATP and nH values (Hill interaction coefficient) decreased from 0.45 to 0.05 mM, and from 4 to 2, respectively, with increase in Mg2+ concentration. Transition metal-ATP complex also activated AMP nucleosidase, but a potent activation of the enzyme was followed by a progressive decrease in activity as the concentrations of transition metals increase. The enzyme fully activated in the presence of Mg2+ was inhibited by the higher concentrations of transition metals with the identical I0.5 values when Mg2+ was present. These results suggest the presence of two classes of binding sites for divalent cations. One is the activating site for ATP-metal complex, which is suggested to be commonly occupied by alkaline earths and transition metals. The other sites are those for free metal binding, the sites for free alkaline earths and free transition metals are activating and inhibitory sites, respectively.

Adenosine Monophosphate↗
PubMed1980

Renin precursor and its activation mechanism in hog kidney.

1. A completely inactive renin was isolated from hog kidney extract by affinity chromatography on pepstatin-aminohexyl-Sepharose and on an Affi-Gel Blue column. 2. This inactive renin had a molecular weight of 43 000 +/- 1500 as determined by gel filtration on Ultrogel AcA 44. Upon activation with trypsin, its molecular weight fell to 41 000 +/- 1400. 3. The inactive renin lacked the ability to bind renin-binding substance whereas trypsin-activated renin was able to bind the renin-binding protein and to form high-molecular-weight renin. 4. Chymotrypsin as well as trypsin could activate the inactive renin although less effectively. 5. The active renins generated from the inactive renin by the action of different proteolytic enzymes differed in their net charge, reflecting the specificities of the proteases used; the isoelectric points of the native, the trypsin-activated and the chymotrypsin-activated forms of renin occurred at pH 5.3, 5.1 and 4.8 respectively.

Animals↗