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Biomedical subjects

M C Scrutton

Publications and source records attributed to M C Scrutton.

At least 91 records · Page 5Linked to original sources
PubMed1975

Mode of action of the macrolide-type antibiotic, chlorothricin. Effect of the antibiotic on the catalytic activity and some structural parameters of pyruvate carboxylases purified from rat and chicken liver.

The macrolide-type antibiotic chlorothricin inhibits pyruvate carboxylases purified from rat liver, chicken liver and Azotobacter vinelandii. Under standard assay conditions the concentration of chlorothricin required for half-maximal inhibition of oxalacetate synthesis is 0.26 mM (rat liver), 0.12 mM (chicken liver), and 0.5 mM (Azobacter vinelandii). Inhibition by chlorothricin appears non-competitive in character when measured as a function of the concentration of the substrates of the pyruvate carboxylase reaction as well as of CoASAc and Mg2+. This pattern of inhibition suggests that this antibiotic interacts at unique sites on chicken and rat liver pyruvate carboxylase which are distinct from both the catalytic and activator sites. Interaction of chlorothricin with the two vertebrate liver pyruvate carboxylases differs from the effect exerted by this antibiotic on pyruvate carboxylase purified from Azotobacter vinelandii. A sigmoidal relationship between initial velocity and inhibitor concentration is observed for the vertebrate enzymes under most conditions whereas a hyperbolic profile characterizes the concentration dependence of inhibition of the Azotobacter vinelandii enzyme by chlorothricin. In the case of rat liver pyruvate carboxylase chlorothricin does not alter the extent of cooperativity in the relationship between initial rate and CoASAc concentration. However, a small but significant increase of the Hill coefficient from a value of 2.7 in the absence of antibiotic to that of 3.3 in the presence of 0.5 mM chlorothricin is observed for chicken liver pyruvate carboxylase. Chlorothricin decreases the rate of inactivation observed when rat liver pyruvate carboxylase is incubated with trinitrobenzenesulfonate and when chicken liver pyruvate carboxylase is incubated at 2 degrees C. The maximal decrease in inactivation observed in the presence of saturating concentrations of antibiotic is 50% for cold inactivation of the chicken liver enzyme and 60% for inactivation of the enzyme from rat liver by trinitrobenzenesulfonate. In both cases a sigmoidal relationship is observed between inactivation rate and chlorothricin concentration. These data as well as the initial rate studies suggest that multiple interacting sites for this antibiotic are present on the vertebrate liver pyruvate carboxylases. The occupancy of these sites appears to cause significant distortion of both the catalytic and the activator sites.

Adenosine Triphosphate↗
PubMed1975

Copper infusion therapy in trichopoliodystrophy.

The effect of repeated intravenous infusions of cupric salts was studied in two patients (cousins) with trichopoliodystrophy identified at the ages of 3 days and 2 and-one-half mo, respectively. The intravenous doses of copper were gradually increased and normal or near-normal serum values were achieved after 150 mug/Cu2+/kg were administered daily for 5 days. At that time the hepatic concentration of copper in the two patients increased from 14 to 38 mug/gm of dry weight from 7 to 45 mug/gm of dry weight, respectively, and the muscle homogenate exhibited the capacity to oxidize pyruvate-3-14C. Continued infusions of cupric salts in doses of 190-220 mug/kg/day once or twice weekly were necessary to maintain elevated hepatic and serum concentrations of copper. At 6 mo of age the younger infant had reached a functioning level of 4 mo. The older infant demonstrated progressive loss of neurologic functions and died at 15 mo of age. These observations suggest that the neurologic and biochemical dysfunctions of trichopoliodystrophy may be altered by infusion of cupric salts early in the course of the disease.

Age Factors↗
PubMed1975

Metal ion contents of gel-filtered platelets from patients with storage pool disease.

Platelets from nine patients with storage pool disease (SPD) and from ten control subjects were isolated by gel filtration into a suspension medium permitting the direct determination of platelet Mg-2+, Ca-2+, and K+ levels. The total intracellular levels of ATP and ADP, as well as the incorporation patterns of 14-C-adenine into the metabolic nucleotide pool, were also determined in these platelet suspensions. The gel-filtered platelets (GFP) from SPD patients exhibited slightly lowered levels of ATP and substantially reduced amounts of ADP, in agreement with previous studies using PRP suspensions. Diminished aggregation responses to ADP, epinephrine, and to collagen in particular, similar to those observed previously in PRP, were obtained in GFP from SPD patients. However, GFP from the patients exhibited more variable aggregation responses to addition of ADP and epinephrine than did GFP from the control subjects. Increases in the extent of radioactive hypoxanthine formation, observed previously in normal platelets as a result of isolation into the suspension medium used in these studies, were significantly reduced in the GFP from SPD patients. The levels of platelet Mg-2+ and K+ determined in GFP from the patients were not significantly different from the levels of these ions in GFP from control subjects. However, substantial reductions in platelet Ca-2+ were found in the SPD platelets. A strong correlation was obtained between this reduction in platelet Ca-2+ and the reduction in ADP in these platelets. No such correlation was apparent between the ATP and Ca-2+ deficiencies. These results suggest that a major portion of platelet Ca-2+ may be located in the dense granules and support previous hypotheses that granular ADP and/or Ca-2+ may play a role in the release reaction. The finding of normal levels of platelet Mg-2+ and K+ in SPD platelets, however, suggests that these latter ions are not located in the dense granules.

Adenine↗
PubMed1975

Content and thrombin-induced release of acid hydrolases in gel-filtered platelets from patients with storage pool disease.

The levels of four acid hydrolases, beta-N-acetyl glucosaminidase, beta-glucuronidase, beta-galactosidase, and acid phosphatase, and the extent of their release (release II) by thrombin was determined in platelets from nine normal subjects, nine patients with storage pool disease, and in normal platelets which had been exposed to aspirin. The levels of all four hydrolases were normal in patients with SPD. However, release of three of these hydrolases (acid phosphatase was an exception) by low concentrations of thrombin (0.015 and 0.04 U/ml) was decreased in the patients as a group, although considerable variation in the extent of release of each enzyme was noted. In contrast, aspirin failed to inhibit release II in normal platelets (except for a slight impairment in the release of beta-N-acetyl glucosaminidase), although release I (serotonin, ATP and ADP) was inhibited. All release defects could be overcome by using higher concentrations of thrombin (0.2 U/ml). The normal levels of acid hydrolases in the platelets of patients with SPD (who are deficient in the platelet dense granules) suggest that these enzymes are not normally stored in the dense granules, but rather in alpha-granules. The findings also support the conclusions of previous studies that the release reaction is impaired in SPD. This release defect appears to be different from that seen in normal platelets after exposure to aspirin.

Acetylglucosaminidase↗
PubMed1975

Early, reversible plasma membrane injury in galactosamine-induced liver cell death.

Administration to rats of D-galactosamine (400 mg/kg) produces liver cell death that develops during the first 24 hours. Plasma membranes isolated within the first few hours from these animals show a 40% reduction in 5'-nucleotidase activity and a two-fold increase in maximum negative ellipticity determined by circular dichroism. Simultaneous administration of uridine prevents liver cell death and these early alterations in the plasma membranes. Uridine also prevents cell death if administered for up to 3 hours after galactosamine. The 5'nucleotidase activity reduced when uridine is administered for up to 2-1/2 hours after galactosamine. Changes in the liver calcium ion concentration accompany these plasma membrane alterations. Uridine will prevent and reverse the changes in calcium content in parallel to its ability to reverse the membrane alterations. The significance of these findings with respect to the mechanism of galactosamine-induced liver cell death is discussed.

Animals↗
PubMed1975

Studies on gel-filtered human platelets: isolation and characterization in a medium containing no added Ca2+, Mg2+, or K+.

We have adapted the gel filtration technique for separation of human platelets from the plasma constituents to permit use of an eluant containing no added Ca2+, Mg2+, and K+, and hence allow direct determination of the intracellular concentrations of these ions in the isolated platelets. The eluant employed is modified Ca2+-free Tyrode's buffer which contains Sr2+ (0.2 mM) as a substitute for Mg2+ and lacks added K+. The functional metabolic, and morphological properties of these isolated platelets have been determined ael-filtered platelets (GFP) to low concentrations of ADP and adrenaline was qualitatively similar to that of platelet-rich plasma (PRP). However, a slower response was observed for the GFP. This rate difference was partially or completely reversed by addition of apyrase to the medium. Analysis of the total adenine nucleotide content and the pattern of 14C incorporation into the metabolic adenine nucleotide pool indicated that isolation in this medium caused to significant change in the ATP and ADP contents or in the adenylate energy change in comparison with the PRP. However, a significant increase in the extent of hypoxanthine production from ATP was noted in GFP isolated in media lacking Mg2+. Inclusion of Mg2+ in the elution media prevented this increased hypoxanthine production. The intracellular concentrations of Ca2+, Mg2+, and K+ of the GFP as determined by atomic absorption analysis were in good agreement with the values obtained for platelets separated from plasma by high-speed centrifugation. Platelet Ca2+ and Mg2+ levels remained stable despite the lack of significant extracellular levels of these ions. However platelet K+ fell to about 30 per cent of its initial value after incubation of 90 minutes at 23 degrees C. and a coincident increase was observed in extracellular K+ concentration. This procedure for platelet isolation may be of particular value for studies on the role of Ca2+, Mg2+, and K+ in platelet physiology and metabolic processes.

Adenine↗