No abstract

The concentration of tritiumlabeled adrenaline was determined in various areas of cat brain after intravenous infusion. It did not exceed that expected from the blood content of the tissue except in the hypothalamus, where small but significant amounts of H(3)-adrenaline were found.

PSEUDO-CHOLINESTERASE CONCENTRATION 311 3. The pseudo-cholinesterase concentrations have been expressed on the basis ofenzyme activity under standard conditions. The concentration of pseudocholinesterase in the particular samples of full serumused were as follows: horse serum 8 8 x 10-8 M; human serum, 7*9 x 10-8M; female mouse serum, 5-8 x 10-8M; dog serum, 4-6 x 10-8M; female rat serum, 17 x 108M. 4. The pseudo-cholinesterases from mouse, rat, horse, human and dog serum form a series in which the ratio of pseudo-cholinesterase activity towards 0-06M-acetylcholine over that towards 0-006Mbenzoylcholine diiminishes progressively from 8-2 to 1-6. In this same series, the absolute activity of the pseudo-cholinesterases towards acetylcholine becomes progressively smaller. Other characteristics of the pseudo-cholinesterases also vary considerably from one type of pseudo-cholinesterase to another, but do not show any correlation to the above series. 5. The significance of these results has been discussed with respect to the concept of the pseudocholinesterases as a special group of closely related enzymes. The author is indebted to Dr B. Mendel for his valuable criticisms and suggestions, to Miss M. de Jonge and Miss E.

No abstract

No abstract

No abstract

Abstract— (1) The glutaminase activity of a guinea pig brain dispersion (a 1500g supernatant solution) was tested at pH 7.5 in the presence of a series of organic acids at 20 mm with or without the further addition of 7.5 mm‐phosphate. (2) In the absence of phosphate, glutaminase activity was strongly enhanced by tricarboxylic acids, less strongly by dicarboxylic acids, and slightly, if at all, by monocarboxylic acids. Acidic amino acids were intermediate between mono‐ and dicarboxylic acids. In the presence of 7.5 mm‐phosphate, the addition of 20 mm organic acids resulted in strong potentiation of the activating effect in many cases. The activating effect of even the most active of the organic acids tested, citrate, was only about half of the effect of an equimolar amount of phosphate. (3) At phosphate concentrations approaching the saturation level for activation, the further addition of citrate was without effect. (4) Glutaminase was strongly activated by ITP which was about three times as active as inorganic phosphate. IMP was less active than inorganic phosphate and creatine phosphate had only slight activity which seemed to be accounted for by its content of inorganic phosphate. (5) Glutaminase was activated by fluoride, in the presence as well as in the absence of added phosphate. Chloride, bromide, and iodide, at 100 mm, produced increasing inhibition of the phosphate‐activated reaction. The inhibiting effect of iodide was qualitatively competitive with phosphate. (6) The effects of various other potential inhibitors and activators, including SH‐reagents, d‐glutamine, several amino acids, and amino acid derivatives were studied. (7) The results have been discussed with particular reference to their significance in elucidating the natural function of brain glutaminase. It has been suggested that glutaminase is an allosteric enzyme and that the secondary active site requires a reaction with three anionic groups for full activation.

IT WAS shown previously (WEIL-MALHERBE, AXELROD and TOMCHICK, 1959) that circulating [3H]epinephrine did not cross the blood-brain barrier to any significant extent except in the hypothalamic region. Even there the uptake was slight in comparison with extracerebral tissues (AXELROD, WEIL-MALHERBE and TOMCHICK, 1959).These experiments have now been extended to [3H]norepinephrine; furthermore the effect of a series of drugs on the uptake of circulating [3H]norepinephrine by the pituitary gland and by various areas of the brain has been studied. Preliminary accounts of this work have been presented at two symposia (WEIL-MALHERBE, 1960; WEIL-MALHERBE, WHITBY and AXELROD, 1961).