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Biomedical subjects

M M King

Publications and source records attributed to M M King.

At least 73 records · Page 4Linked to original sources
PubMed1982

Specificity of a phenobarbital-induced cytochrome P-450 for metabolism of carbon tetrachloride to the trichloromethyl radical.

Evidence is presented which demonstrates that the first polypeptide to disappear in liver microsomes of phenobarbital-induced rats treated with CC14 was the 52,000 dalton p-450 cytochrome. Data are also presented which show that this form of cytochrome P-450 was capable of generating the trichloromethyl radical from CCl4 in a reconstituted system containing the purified cytochrome, NADPH-cytochrome P-450 reductase, NADPH, CCl4, and the spin-trapping agent, phenyl-t-butyl nitrone. Other cytochrome P-450 fractions not containing the 52,000 dalton form did not produce this radical. The formation of this highly reactive radical may have resulted in localized damage to the cytochrome, causing the cytochrome either to be released from the microsomal membrane or to form large aggregates which did not migrate in the gel electrophoretic procedures employed.

Animals↗
PubMed1981

Synergistic activation by Ca2+ and Mg2+ as the primary cause for hysteresis in the phosphorylase kinase reactions.

A synergistic activation of phosphorylase kinase by Ca2+ plus Mg2+ was found to be the primary cause of the hysteresis, or lag, in the phosphorylase kinase reaction. Preincubation of the enzyme for short times with Ca2+ plus Mg2+ resulted in an approximately 7-fold increase in the kinase activity in subsequent assays with phosphorylase b or phosphorylase kinase as substrates, whereas preincubation with each metal ion by itself had no effect. Maximal activation through preincubation with Ca2+ plus Mg2+ occurred in 1 min 45 s and was readily reversed by chelation of both metal ions. As a result of the activation, the progress curve of phosphorylase b conversion at pH 6.8 was found to be nearly linear. Activation by Ca2+ plus Mg2+ was not apparent when subsequent assays were carried out at pH 8.2, or when previously autophosphorylated enzyme was used. Furthermore, the synergistic activation was found to occur significantly slower and/or to decrease in the presence of ATP, phosphorylase b, beta-glycerophosphate, and inorganic phosphate. How the synergistic activation by Ca2+ plus Mg2+ relates to autophosphorylation and the lag in the phosphorylase kinase reaction is discussed.

Animals↗
PubMed1981

Interaction of phosphorylase kinase with the 2',3'-dialdehyde derivative of adenosine triphosphate. 1. Kinetics of inactivation.

The 2',3'-dialdehyde derivative of ATP (oATP) was found to be a valid affinity label for rabbit skeletal muscle phosphorylase kinase. Inactivation by oATP at pH 6.8 followed pseudo-first-order and saturation kinetics. An apparent Ki of approximately 6.7 microM was obtained in the presence of 0.6 mM Ca2+ plus 10 mM Mg2+. Protection against the rate of inactivation was provided by the natural substrate ATP. In addition, at pH 8.2, oATP could be used as a substrate to phosphorylate phosphorylase b, thus providing evidence that oATP can bind to the active site of phosphorylase kinase. Inactivation of phosphorylase kinase by oATP was sensitive to various effectors of the enzyme such as Ca2+, Mg2+, and pH. Ca2+ plus Mg2+ synergistically enhanced the rate of inactivation severalfold; each metal ion by itself had little effect on the rate of inactivation. This synergism was seen both at pH 6.8 and at pH 8.2; however, the rates of inactivation were much greater at pH 6.8. The enhancement of inactivation by Ca2+ plus Mg2+ was also more pronounced with activated than with nonactivated kinase.

Adenosine Triphosphate↗
PubMed1981

Interaction of phosphorylase kinase with the 2',3'-dialdehyde derivative of adenosine triphosphate. 2. Differential inactivation measured with various protein substrates.

The 2',3'-dialdehyde derivative of ATP was used as an affinity label to inactivate phsosphorylase kinase in either the presence or absence of Ca2+ and Mg2+ ions. Following inactivation, the residual activity of phorphorylase kinase toward various protein substrates was measured and compared with that retained for conversion of phosphorylase b. Three different classes of substrates were distinguished by this analysis. For the first class (glycogen synthase), inactivation proceeded at the same rate as that measured with phosphorylase conversion, regardless of whether the inactivation was carried out in the presence or absence of the metal ions. For the second class of substrates (troponin I and troponin T), inactivation of the kinase in either the presence or absence of the metals was much more rapid with phosphorylase as substrate. Phosphorylation of the third class of substrates (phosphorylase kinase itself and a synthetic tetradecapeptide) was inactivated in parallel with phosphorylase b when modification was performed in the absence of metals; however, inclusion of Ca2+ and Mg2+ ions in the inactivation mixture caused activity toward phosphorylase b to be lost more rapidly than that toward the alternative substrates. Our results are consistent with a model in which glycogen synthase and phosphorylase b are preferentially phosphorylated at one type of catalytic site in phosphorylase kinase and troponin I and troponin T at another.

Adenosine Triphosphate↗
PubMed1981

Nonsteroidal estrogens and antiestrogens: biological activity of cyclopropyl analogs of stilbene and stilbenediol.

The estrogenic, antiestrogenic, and receptor binding activity of a series of cyclopropyl analogs of stilbene and stilbenediol were determined using the uterotropic assay in the mouse and the receptor binding assay with rat uterine cytosol. One compound, 1,1-dichloro-cis-2,3-diphenylcyclopropane (II), displayed antiestrogenic activity in vivo with a low affinity for the estrogen receptor in vitro and showed tumor remission activity on 7,12-dimethylbenz(a)anthracene-induced estrogen-dependent rat mammary tumors. Compounds VIII, IV, and V (in that order) exhibited the greatest estrogen activity in the mouse and the greatest receptor binding activity in vitro. Compound VIII exhibited antifertility activity in the mouse.

Animals↗
PubMed1981

Comparison of the effect of butylated hydroxytoluene on N-nitrosomethylurea and 7,12-dimethylbenz[a]-anthracene-induced mammary tumors.

The antioxidant butylated hydroxytoluene (BHT) when fed at a level of 0.3% in a defined semi-purified diet was found to decrease mammary tumor incidence in female Sprague-Dawley rats induced by 7,12-dimethylbenz[a]-anthracene (DMBA). however, no effect of BHT on tumor incidence was seen in animals consuming the same diet, under identical experimental conditions, but treated with the carcinogen nitrosomethylurea (NMU). Differences in effectiveness of BHT as a tumor inhibitor in the 2 model systems, and thoughts as to a possible mechanism of action with regard to BHT are discussed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1981

Differences in airway reactivity in normal and allergic sheep after exposure to sulfur dioxide.

The effect of breathing 5 ppm sulfur dioxide (SO2) on airway reactivity was studied in both normal and allergic conscious sheep. Allergic sheep were defined as animals in which inhalation of Ascaris suum extract resulted in bronchospasm as evidenced by an increase in mean pulmonary flow resistance (RL), hyperinflation, and a fall in dynamic compliance. Airway reactivity was assessed by measuring the increase of RL after 18 breaths of 0.25% carbachol (c), from an initial RL value obtained after 18 breaths of buffered saline (s) [RL(c-s)]. RL and RL(c-s) were determined prior to, immediately after, and 24 h after exposure to 5 ppm SO4 for 4 h. In both groups RL remained unchanged after SO2 exposure. Prior to exposure, RL(c-s) was not significantly different in seven normal (0.3 +/- 0.1) and seven allergic sheep [0.4 +/- 0.2 (SD) cmH2O X l-1 X s], and there was no significant change in RL (c-s) immediately after SO2 exposure in either group. Twenty-four h later, RL(c-s) RL(c-s) increased to 0.7 +/- 0.8 (P less than 0.2) in normal and to 1.8 +/- 0.9 cmH2O X l-1 X s (P less than 0.01) in allergic sheep. Because the increase in RL(c-s) after 24 h was greater (P less than 0.01) in allergic than in normal sheep, we conclude that SO2 exposure increased airway reactivity more in the former than in the latter.

Animals↗
PubMed1981

Effect of pharmacologic agents on antigen-induced decreases in specific lung conductance in sheep.

The purpose of this investigation was to determine the primary mediators responsible for the decrease in specific lung conductance (SGL) after airway challenge with Ascaris suum antigen in allergic sheep. On different occasions, separated by 10 to 14 days, pulmonary resistance and thoracic gas volume were measured in 5 sheep with Ascaris suum hypersensitivity before and for 2 h after a standard inhalation challenge with this antigen. Initially and at the end of the study, inhalation challenge decreased mean SGL to 38 and 44% of baseline, respectively. Pretreatment by intravenous injection of the H1 receptor antagonist chlorpheniramine (2 mg/kg) completely prevented the antigen-induced decrease in SGL. Similar results were obtained with inhalation of the mediator release blocking agent, disodium cromoglycate (1 mg/kg), prior to antigen challenge. The decrease in SGL after inhalation challenge was not modified by pretreatment with the H2 receptor antagonist, metiamide (3 mg/kg), the anticholinergic agent, atropine (0.2 mg/kg), the prostaglandin synthetase inhibitor, indomethacin (2 mg/kg) by intravenous injection, or with inhalation of FPL-55712 (1% solution), an antagonist of slow-reacting substance of anaphylaxis (SRS-A). We concluded that during allergic bronchoconstriction in sheep (1) the decrease in SGL is mediated by histamine via H1 receptors, (2) other liberated or activated mediators including SRS-A do not decrease SGL, and (3) cholinergic reflex mechanisms are not involved in this response.

Airway Resistance↗
PubMed1981

The influence of dietary fat and non-specific immunotherapy on carcinogen-induced rat mammary adenocarcinoma.

The incidence of mammary adenocarcinoma in Sprague-Dawley female rats, caused by the carcinogen 7,12-dimethylbenz(alpha)anthracene, was influenced by the level of dietary fat fed after exposure to carcinogen. Carcinogen was given by stomach tube to 50-day-old rats, and tumors were evaluated when rats were 9 months old. Rats on diets containing 20% unsaturated fat had a tumor incidence of 97%, while rats changed to a low-fat diet (2% unsaturated fat) three or four weeks after exposure to the carcinogen had an incidence of 45%. Some rats on each diet were given two treatments with the methanol extraction residue of Bacillus Calmette-Guerin, either three and five weeks after carcinogen or four and six weeks after carcinogen. Tumor incidence in the treated group and the untreated group was the same when rats were maintained on the high-fat diet, but tumors in the treated group were larger and the disease was more severe by histological criteria. These tumors were more anaplastic and many were extensively infiltrated with lymphocytes compared to the untreated group. Tumor incidence was significantly lower in rats changed to the low-fat diet (45%) than in those on the high-fat diet (97%), and tumor incidence was reduced to 20% when rats changed to the low-fat diet were treated with methanol extraction residue. The treated group had less severe disease than the untreated group on the low-fat diet. Only half the tumor-bearing rats in this group had malignant tumors, and none were invasive. Methanol extraction residue protected most rats on the low-fat diet against mammary adenocarcinoma, and reduced the severity of disease in those rats that did develop tumors. Methanol extraction residue treatment provided no protection, and even increased the severity of disease, in rats on the high-fat diet.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1981

Evidence that the effectiveness of antioxidants as inhibitors of 7,12-dimethylbenz(a) anthracene-induced mammary tumors is a function of dietary fat composition.

A study of tumor incidence and tumor growth rates in 7,12-dimethylbenz(a)anthracene-treated female Sprague-Dawley rats fed different types and amounts of dietary fat indicates that the difference in tumor incidence may be a reflection of marked differences in the growth of neoplastic clones to a palpable size within the time frame of the study. In addition, the observation is made that some antioxidants which inhibit tumor development in animals fed commercial rations are not effective when given in purified diets.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1979

Inhibition of lymphocyte function in rats fed higher-fat diets.

Concanavalin A-induced blastogenesis of spleen lymphocytes was significantly inhibited when lymphocytes from rats on a high-polyunsaturated-fat diet were compared to lymphocytes from rats on a low-fat diet. Responsiveness was dependent on source of serum since lymphocytes from rats fed a low-fat diet were suppressed in serum from rats fed a high-polyunsaturated-fat diet. Alternatively, lymphocytes from rats on a high-polyunsaturated-fat diet were more responsive in serum from low-fat-fed rats compared to their response in autologous serum. One of the inhibiting factors in serum was the lipoprotein fraction; however, rats on a high-polyunsaturated-fat diet probably had additional inhibitors in their serum. While tumor incidence was highest in rats with the least responsive lymphocytes was highest in rats with the least responsive lymphocytes and lowest in rats with the most responsive lymphocytes, the significance of the observation is not known.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1975

Singlet oxygen production associated with enzyme-catalyzed lipid peroxidation in liver microsomes.

Evidence for the formation of singlet oxygen during the oxidation of NADPH by liver microsomes is presented. The evidence is based primarily on the enzyme-dependent formation of dibenzoylethylene from diphenylfuran, a reaction which is specific for singlet oxygen. The apparent formation of singlet oxygen is coupled to the occurrence of peroxidation of microsomal lipid, a phenomenon known to be associated with NADPH oxidation by the particles. Both the peroxidation of lipid and the apparent formation of singlet oxygen are related to the amount of Fe3+ present in the system and the results are consistent with the possibility that the singlet oxygen formed by this system is derived from the breakdown of lipid peroxides. If 1O2 is formed from breakdown of lipid peroxides, it would be dependent on O-/-2 formation because superoxide anion has been shown to undergo reactions in this system which generate extremely reactive free radicals (probably hydroxyl) that initiate lipid peroxidation. These peroxides are quite unstable and their degradation may be the source of 1O2. We have consistently observed that O-/-2 itself is not a reactive radical with respect to lipids or radical scavengers. Hence, O-/-2 cannot be the radical which initiates lipid peroxidation on which 1O2 generation appears to depend. The results may offer at least part of the explanation for the dietary requirement for alpha-tocopherol which not only scavenges free radicals but quenches singlet oxygen as well. This report also includes description of studies indicating that another enzyme, xanthine oxidase, which forms superoxide anion during its activity under aerobic conditions, does not form singlet oxygen during its function. This finding is in contrast to reports of others which indicate that xanthine oxidase activity does produce 1O2.

Aniline Compounds↗