AMINO ACID DISTRIBUTION AND INCORPORATION INTO PROTEINS IN ISOLATED, ELECTRICALLY-STIMULATED CEREBRAL TISSUES

—The uptake of radioactive amino acid by incubated cerebral cortex slices is found to be a first order process. Incorporation of the radioactive amino acid into tissue protein is from a precursor pool that has first equilibrated with the intracellular endogenous free amino acids. Ways of calculating the amino acid incorporation in molar quantities from the observed incorporation of radioactivity are discussed, and it is concluded that the specific radioactivity of the intracellular acid-soluble fraction is the best basis for such estimates. The in vitro incorporation of leucine into tissue protein is estimated to be approximately 1±2 mμnol/mg protein/h, and of valine 0±4 mμmol/mg protein/h. Addition of free amino acids to the media had little or no effect on the calculated rates of incorporation. On incubation for 1 h the total free valine in tissue and medium increased by 0±43 μmol/g and leucine increased by 0±55 μmol/g. Estimates of amino acid incorporation based on the specific radioactivity of the media amino acids can give misleading results if this considerable release of amino acids into the medium is not taken into account. Electrical stimulation of neocortical slices with a variety of types of pulses was either without effect or decreased incorporation into portein. The decrease could not be directly correlated with changes in tissue K⁺ nor with the utilization of ATP. Mild, local stimulation of the lateral olfactory tract of piriform cortex slices was without effect on tissue phosphocreatine, K⁺ or amino acid incorporation.     

Protein-bound phosphorylserine in acid hydrolysates of brain tissue. The determination of [32P]phosphorylserine by ion-exchange chromatography and electrophoresis

1. Partial acid hydrolysates of proteins derived from cortical slices of guinea-pig brain were divided into two parts and fractionated by ion-exchange chromatography and high-voltage electrophoresis. 2. The apparent yield of protein-bound phosphorylserine by the ion-exchange method was about three times that obtained by electrophoresis. 3. The specific radioactivity of phosphorylserine isolated from (32)P-labelled slices by electrophoresis was twice that isolated by chromatography. 4. The discrepancies were found to be due to the presence of unlabelled phosphates of unknown composition in the ;phosphorylserine' fraction obtained by the ion-exchange method. 5. Electrical stimulation of slices respiring in the presence of [(32)P]phosphate increased the specific radioactivity of the total phosphate in the chromatographic ;phosphorylserine' fraction by 53+/-11%, as compared with only 19+/-5% for the phosphorylserine isolated by electrophoresis.     

Reversible binding of phytomitogens to lymphocytes

The reversible binding of phytohaemagglutinin and concanavalin A to lymphoyctes and red cells was studied by radiolabelling techniques. The quantity of mitogen bound was dependent on the temperature, concentration and duration of the mitogen pulse. Dissociation of mitogen occurred rapidly from red cells and lymphocytes and the kinetics of release from lymphoid cells displayed two components with different half lives. There was suggestive evidence that the binding component with the longer half life was related to lymphocyte activation. The induction of DNA synthesis in lymphocytes required at least 20-hr exposure to the mitogens. These data indicate that the binding of mitogen is a complex reversible process in which association and dissociation are critically dependent on the temperature, concentration and duration of the mitogen pulse.     

Acute Abdominal Pain in Childhood,with Special Reference to Cases not due to Acute Appendicitis

Appendicitis is not the only common cause of acute abdominal pain in childhood. Almost equally common is an acute episode which in its early stages resembles acute appendicitis but which subsides without treatment in 24 to 48 hours. The clinical features of this syndrome are contrasted with those of appendicitis. The two conditions cannot always be distinguished on clinical grounds, leading to admission to hospital for observation and the finding of a normal appendix in 14% of operations for suspected appendicitis. Reasons are given for abandoning attempts to diagnose acute mesenteric adenitis at the bedside.