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Biomedical subjects

D E Richards

Publications and source records attributed to D E Richards.

At least 55 records · Page 3Linked to original sources
PubMed1979

The effect of dietary disulfiram upon the tissue distribution and excretion of 14C-1,2-dibromoethane in the rat.

Dietary disulfiram enhances the toxicity of inhaled 1,2-dibromoethane in rats. This study was undertaken to determine whether the differential toxicity noted was associated with alterations in the levels of the compound and/or its metabolites in the target organs. A comparison of the levels of 14C in selected tissues of male rats, with and without dietary disulfiram, following the oral administration of 14C-1,2-dibromoethane was made. The results indicated that levels of radioactivity in the target organs of animals in the disulfiram group were significantly elevated both at 24 and 48 hours following compound administration. The data indicate a direct correlation between tissue levels and the enhancement of toxicity noted in the disulfiram-treated rats in the inhalation study. A significant elevation in the levels of radioactivity in washed liver nuclei obtained from animals receiving dietary disulfiram was also noted, suggesting a relationship between nuclear uptake and the increased incidence of liver tumors appearing in the disulfiran group in the inhalation study.

Animals↗
PubMed1978

Two classes of site for ATP in the Ca2+-ATPase from human red cell membranes.

(1) The response of the Ca2+-ATPase activity from human red cell membranes to ATP concentrations can be represented by the sum of two Michaelis-like curves: one with a Km of 2.5 micrometer and the other with a Km of 145 micrometer. (2) The maximum Ca2+-ATPase activity elicited by occupation of the site with lower Km represents about 10% of the activity attainable at non-limiting ATP concentrations. (3) 30--50% of the Ca2+-ATPase activity with lower Km remains in the absence of Mg2+ . Mg2+ increases V and the maximum effect of Ca2+, having no effect on the apparent affinities for ATP and Ca2+. (4) The large increase in Ca2+-ATPase activity which results from the occupation of the site with higher Km only takes place when Mg2+ is present. (5) Results are compatible with the idea that the Ca2+-ATPase from human red cell membranes has two classes of site for ATP binding, both of which are occupied when the enzyme catalyzes the hydrolysis of ATP at maximum rate. (6) The properties of the high affinity site suggest that this is the catalytic site of the Ca2+-ATPase. It is proposed that binding of ATP at the low affinity site regulates the turnover of the system.

Adenosine Triphosphatases↗
PubMed1977

ATPase and phosphatase activities from human red cell membranes: I. The effects of N-ethylmaleimide.

In human red cell membranes the sensitivity to N-ethylmaleimide of Ca2+-dependent ATPase and phosphatase activities is at least ten times larger than the sensitivity to N-ethylmaleimide of (Na+ + K+)-ATPase and K+-activated phosphatase activities. All activities are partially protected against N-ethylmaleimide by ATP but not by inorganic phosphate or by p-nitrophenylphosphate. (ii) Protection by ATP of (Na+ + K+)-ATPase is impeded by either Na+ or K+ whereas only K+ impedes protection by ATP of K+-activated phosphatase. On the other hand, Na+ or K+ slightly protects Ca2+-dependent activities against N-ethylmaleimide, this effect being independent of ATP. (iii) The sensitivity to N-ethylmaleimide of Ca2+-dependent ATPase and phosphatase activities is markedly enhanced by low concentrations of Ca2+. This effect is half-maximal at less than 1 micron Ca2+ and does not require ATP, which suggests that sites with high affinity for Ca2+ exist in the Ca2+-ATPase in the absence of ATP. (IV) Under all conditions tested the response to N-ethylmaleimide of the ATPase and phosphatase activities stimulated by K+ or Na+ in the presence of Ca2+ parallels that of the Ca2+-dependent activities, suggesting that the Ca2+-ATPase system possesses sites at which monovalent cations bind to increase its activity.

Adenosine Triphosphatases↗
PubMed1977

ATPase and phosphatase activities from human red cell membranes: II. The effects of phospholipases on Ca2+-dependent enzymic activities.

Treatment of human red cell membranes with pure phospholipase A2 results in a progressive inactivation of both Ca2+-dependent and (Ca2+ + K+)-dependent ATPase and phosphatase activities. When phospholipase C replaces phospholipase A2, Ca2+-dependent ATPase activity and Ca2+-dependent phosphorylation of red cell membranes are lost, while Ca2+-dependent phosphatase activity is enhanced and its apparent affinity for Ca2+ is increased about 20-fold. Activation of Ca2+-dependent phosphatase following phospholipase C treatment was not observed in sarcoplasmic reticulum preparation. Phospholipase C increases the sensitivity of the phosphatase to N-ethylmaleimide but has little effect on the kinetic parameters relating the phosphatase activity to substrate and cofactors, suggesting that no extensive structural disarrangement of the Ca2+-ATPase system has occurred after incubation with phospholipase C.

Adenosine Triphosphatases↗
PubMed1977

ATPase and phosphatase activities from human red cell membranes. III. Stimulation of K+-activated phosphatase by phospholipase C.

Treatment of red cell membranes with pure phospholipase C inactivates (Na+ + K+)-ATPase activity and Na+-dependent phosphorylation but increases K+-dependent phosphatase activity. When phospholipase A2 replaces phospholipase C, all activities are lost. Activation of K+-dependent phosphatase by treatment with phospholipase C is caused by an increase in the maximum rate of hydrolysis of p-nitrophenylphosphate and in the maximum activating effect of K+, the apparent affinities for substrate and cofactors being little affected. After phospholipase C treatment K+-dependent phosphatase is no longer sensitive to ouabain but becomes more sensitive to N-ethylmaleimide. In treated membranes Na+ partially replaces K+ as an activator of the phosphatase. Although ATP still inhibits phosphatase activity, neither ATP, nor ATP+Na+ are able to modify the apparent affinity for K+ of K+-dependent phosphatase in these membranes.

Adenosine Triphosphatases↗
PubMed1975

An evaluation of the inhalation toxicity of one commercial proteolytic enzyme preparation.

The inhalation toxicity of a commercial proteolytic enzyme preparation containing 12% subtilisin Carlsberg was studied in experimental animals. Guinea pigs that had been pretreated by a series of intradermal injections of the enzyme preparation in saline solution died as a result of a single 6-hour exposure to the enzyme preparation at an air concentraion of 41.2 mg/m-3, while normal guinea pigs and pretreated guinea pigs that were dosed with an antihistamine immediately prior to exposure survived. The 6-hour LC50 for pretreated guinea pigs was determined as 24.7 mg/m-3. Normal rats, normal rabbits, and pretreated rabbits survived exposures to the enzyme preparation at concentrations as high as 36.8 mg/m-3. Pathologic examinations revealed changes only in the lungs of the exposed animals. These pulmonary alterations appear to be reversible. A histamine release is suggested as the primary effect of a secondary exposure to this proteolytic enzyme preparation.

Aerosols↗
PubMed1975

Histamine induction and release following proteolytic enzyme exposure.

The mechanism of biologic response from exposure to a 12% subtilisin Carlsberg preparation is shown to be one of histamine release in the guinea pig. Three groups of guinea pigs were pretreated by intradermal injections withsaline solution of (1) the commercial proteolytic enzyme preparation containing 12% subtilisin Carlsberg, (2) an alkaline protease preparation obtain from Aspergillus oryzae that was isolated from cotton dust, or (3) a nonproteolytic mixture of proteins and lipases obtained from cotton seeds. The histamine content of the ling, liver, and ear tissues of guinea pigs that were pretreated with any one of the three preparations showed an in untreated animals. Following challenge by intratracheal injection of a saline solution containing the subtilisin preparation, the guinea pigs pretreated with the same preparation showed a markedly reduced liver histamine level. Challenge by inhalation exposure to the subtilisin preparation of guinea pigs that were pretreated with any one of the above preparations resulted in a lower histamine concentration in the lungs and livers.

Aerosols↗
PubMed1973

Calcium ion-dependent p-nitrophenyl phosphate phosphatase activity and calcium ion-dependent adenosine triphosphatase activity from human erythrocyte membranes.

In the presence of ATP and of Mg(2+), human erythrocyte membranes show a phosphatase activity towards p-nitrophenyl phosphate which is activated by low concentrations of Ca(2+). The effect of Ca(2+) is strongly enhanced if either K(+) or Na(+) is also present. Activation of the p-nitrophenyl phosphate phosphatase by Ca(2+) reaches a half-maximum at about 8mum-Ca(2+) and is apparent only when the ion has access to the inner surface of the cell membrane. Ca(2+)-dependent phosphatase activity can only be observed if ATP is at the inner surface of the cell membrane, and the presence of ATP seems to be absolutely necessary, since either its removal or its replacement by other nucleoside triphosphates abolishes the activating effect of Ca(2+). The properties of the (ATP+Ca(2+))-dependent phosphatase are very similar to those of the Ca(2+)-dependent ATPase (adenosine triphosphatase), also present in erythrocyte membranes, which probably is involved in Ca(2+) transport in erythrocytes. The similarities suggest that both activities may be properties of the same molecular system. This view is further supported by the fact that p-nitrophenyl phosphate inhibits to a similar extent Ca(2+)-dependent ATPase activity and ATP-dependent Ca(2+) extrusion from erythrocytes.

Adenosine Triphosphatases↗