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Biomedical subjects

B Dean

Publications and source records attributed to B Dean.

At least 127 records · Page 7Linked to original sources
PubMed1984

A postbinding inhibitor of insulin action. Increased concentrations in the plasma of non-insulin-dependent diabetic subjects.

"Postreceptor" insulin resistance in persons with non-insulin-dependent diabetes (NIDDM) could be due to an intrinsic defect in insulin-sensitive pathways or to the action of a circulating inhibitor. Since evidence for the former is lacking, we have addressed the question of a circulating inhibitor by examining the effect of plasma and plasma extracts from NIDDM subjects on the lipogenic response of rat adipocytes to insulin. A majority (77%) of plasma samples (1:20 dilution) from unselected, treated NIDDM subjects (N = 69) inhibited insulin-stimulated conversion of 3-3H-glucose to 3H-lipid in rat adipocytes to a greater extent than did control samples (N = 24). The mean +/- SD inhibition by NIDDM plasma (81 +/- 21%) was significantly greater (P less than 0.01) than by control plasma (50 +/- 14%). Diabetic and, to a lesser degree, control plasma both caused a significant decrease in the maximal response of lipogenesis to insulin. Inhibitory activity was extracted into acid/ethanol, present in the flow of a Sep-pak C18 column, heat-stable (56 degrees C for 30 min [plasma], 80 degrees C for 30 min [acid/ethanol]), resistant to proteases, and dialyzable through 1000-dalton-mol wt exclusion dialysis tubing. The inhibition by NIDDM plasma or partially purified inhibitor could not be explained by the presence of insulin antibodies, insulin receptor antibodies, other inhibitors of insulin binding, or the concentrations of known counterregulatory factors. There was no correlation between inhibitory activity and plasma glucose (r = 0.26), insulin (r = 0.33), C-peptide (r = 0.26), or HbA1c (r = 0.26).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1983

Proteolysis in mitochondrial preparations and in lysosomal preparations derived from rat liver.

A method of preparing rat liver mitochondria with low residual contamination by lysosomal proteases is described. Preparations of mitochondria are divided into two equal portions, one of which is supplemented with a lysosomal fraction. The addition of the lysosomal fraction causes an increase in proteolysis of between 26- and 56-fold at pH 5.0 in four similar experiments. This increase matches the increase in the lysosomal marker beta-glucuronidase and indicates that all proteolysis at pH 5.0 is due to enzymes of the lysosomal fraction. Above pH 7.0, the addition of a lysosomal supplement increases proteolysis by 1.5- to 5-fold only, suggesting that in the absence of a lysosomal supplement very little of the observed proteolysis is due to enzymes of lysosomal origin. A method of calculating the contribution to total proteolysis of enzymes of the lysosomal fraction or of the mitochondrial fraction is described. The calculations show that at pH 7.0 and above, more than 93% of the observed proteolysis is due to enzymes originating in the mitochondrial fraction. The results support the view of other workers that rat liver mitochondria contain an endogenous neutral proteolytic system capable of degrading mitochondrial proteins to acid-soluble products.

Amino Acids↗
PubMed1981

Evaluation of home glucose measuring devices.

A large number of glucose-monitoring systems suitable for home use are now available. The Glucochek, an early model (Mk I) and a later (Mk II), the Stan Clark RAHC, the Glucometer, and 20-800 BM glycemie strips were evaluated with regard to accuracy, precision, model variability and operator variability before a particular system was recommended for patient use. Whole blood glucose, on samples samples taken in the Diabetic Clinic of The Royal Melbourne Hospital, Melbourne, was measured with the system under test and in the Biochemistry Department. Accuracy was indicated by the mean of the differences between the two results, and precision by the standard deviation of these differences-the closer these results to zero, the better the system. The 20-800 BM Glycemia strips gave the best results in the hands of an experienced operator, but showed the greatest interoperator differences. These differences decreased when a machine-based system was employed. The Glucochek Mk I did not perform satisfactorily. All the systems tested showed a marked decrease in accuracy and precision when blood glucose levels were greater than 15.0 mmol/L. These results show that a machine is not a necessary part of a home glucose-monitoring system; that patients on home glucose-monitoring must be trained and their results checked against a reference method initially and, ideally, at regular intervals; that home glucose-monitoring in patients with marked hyperglycaemia unreliable.

Blood Glucose↗
PubMed1980

Islet-cell antibodies and beta-cell function in insulin-dependent diabetics.

Residual insulin secretion and islet-cell antibodies were studied in 399 insulin-dependent diabetics with age at onset of between 10--19.9 years (248 patients) or 30--39.9 years (151 patients). We found the prevalence of islet-cell antibodies to be independent of residual beta-cell function as measured by serum C-peptide and age at onset. The cause and role of the persistence of islet-cell antibodies in insulin-dependent diabetics remain obscure.

Adolescent↗
PubMed1973

Oxaloacetate decarboxylases of rat liver.

1. Two oxaloacetate decarboxylases of rat liver are described; one is mitochondrial with no metal ion requirement and activity in the alkaline pH region; the other is cytoplasmic with Mn(2+) or Mg(2+) requirement and activity around pH5. 2. A method for the partial purification of the mitochondrial enzyme is described. 3. The apparent K(m) of the mitochondrial enzyme is 0.23mm. 4. Inhibition of the mitochondrial enzyme by substrate, CoA, acetyl-CoA, citrate and phosphoenolpyruvate is described.

Acetyl Coenzyme A↗
PubMed1969

The effect of inhibitors on the formation of phosphoenolpyruvate by rat liver mitochondria.

1. Rat liver mitochondria oxidizing malate produce PEP (phosphoenolpyruvate) without the addition of ATP or other nucleotides. 2. The addition of oligomycin in the presence of 2,4-dinitrophenol did not abolish PEP formation and in some instances stimulated its formation. 3. Formation of PEP was inhibited by arsenate. 4. Arsenite decreased PEP formation and caused accumulation of pyruvate. 5. Added GTP and ITP had no effect on PEP formation. 6. PEP formed from malate in the presence of GTP and labelled P(i) had a specific radioactivity approximately the same as the P(i) with no contribution from the phosphate of the added GTP. 7. There was no parallelism between the effects of inhibitors on PEP formation from malate and their effects on the assayed activity of PEP carboxykinase. 8. In a direct comparison it was shown that the PEP carboxykinase content of mitochondria was insufficient to account for the PEP formation from malate. 9. Consideration of the kinetic characteristics of PEP carboxykinase and mitochondrial content of oxaloacetate and GTP show that this enzyme cannot account for the PEP formed from malate by mitochondria.

Adenosine Triphosphate↗