Synaptosomal protein synthesis in a cell-free system

—Synaptosomes were isolated from cerebral cortex of young rats and incubated with ¹⁴C-labelled l -leucine in vitro. Amino acid incorporation into proteins of the synaptosomal cytoplasm, mitochondria and membrane components was observed. There was no incorporation into proteins of the vesicles. The protein-synthesizing system was not stimulated by the addition of either ATP or an ATP-generating system. ATP at all concentrations was inhibitory. Two different protein-synthesizing systems operate in the synaptosome. One, sensitive to inhibition by chloramphenicol and related antibiotics, is found in the mitochondrial subfraction and the other, inhibited by cycloheximide, is located either in the membrane components or the synaptosomal cytoplasm. This second system resembles the eukaryotic ribosomal system in its sensitivity to cycloheximide. Both the synaptosomal soluble fraction and the synaptosomal membrane fractions were shown previously to contain RNA. This RNA could function in protein-synthesizing mechanisms in the synaptosome. These results deomonstrate that protein is synthesized in axonal components and show that it is unnecessary to postulate that all axonal protein is supplied by somato-axonal flow.     

Decarboxylation of α-Keto Acids by Streptococcus lactis var. maltigenes

Decarboxylation rates for a series of C-3 to C-6 alpha-keto acids were determined in the presence of resting cells and cell-free extracts of Streptococcus lactis var. maltigenes. The C-5 and C-6 acids branched at the penultimate carbon atom were converted most rapidly to the respective aldehydes in the manner described for alpha-carboxylases. Pyruvate and alpha-ketobutyrate did not behave as alpha-carboxylase substrates, in that O(2) was absorbed when they were reacted with resting cells. The same effect with pyruvate was noted in a nonmalty S. lactis, accounting for CO(2) produced by some "homofermentative" streptococci. Mixed substrate reactions indicated that the same enzyme was responsible for decarboxylation of alpha-ketoisocaproate and alpha-ketoisovalerate, but it appeared unlikely that this enzyme was responsible for the decarboxylation of pyruvate. Ultrasonic disruption of cells of the malty culture resulted in an extract inactive for decarboxylation of pyruvate in the absence of ferricyanide. Dialyzed cell-free extracts were inactive against all keto acids and could not be reactivated.     

THE EFFECT OF INSULIN, ALLOXAN DIABETES, AND ANOXIA ON THE ULTRASTRUCTURE OF THE RAT HEART

Hearts from normal and alloxan diabetic rats were perfused in vitro with a bicarbonate-buffered medium containing glucose. Transport of glucose through the cell membrane was stimulated with insulin or by induction of anaerobiosis. The organs were rapidly fixed and examined by electron microscopy. Transport stimulation was not associated with any increase in the number of sarcolemmal invaginations or subsarcolemmal cytoplasmic vesicles. It was concluded that glucose transport and the effects of insulin or anoxia do not involve pinocytosis. The relationship of pinocytosis to glucose transport is discussed. The appearance of numerous lipid inclusions at the Z line level of the sarcomeres in the diabetic and anoxic myocardia is described.