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INCORPORATION OF AMINO ACIDS INTO PROTEINS IN NEURONAL AND NEUROPIL FRACTIONS OF RAT CEREBRAL CORTEX: PRESENCE OF A RAPIDLY LABELLING NEURONAL FRACTION
Author(s) -
Rose S. P. R.,
Sinha A. K.
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb10759.x
Subject(s) - neuropil , incubation , biochemistry , labelling , cerebral cortex , cell fractionation , phenylalanine , biology , fractionation , in vitro , specific activity , cortex (anatomy) , amino acid , chemistry , central nervous system , endocrinology , enzyme , chromatography , neuroscience
— The time course of incorporation of intraperitoneally injected [ 3 H]lysine and [ 14 C]phenylalanine into neuronal and neuropil proteins has been followed for up to 8 days. At short times after injection (<2 h) the specific activity of the neuronal fraction was higher than that of the neuropil. At longer time intervals, although the total brain specific activity continued to rise, neuronal perikaryal specific activity fell below that of neuropil. Thus the neuronal/neuropil incorporation ratio with [ 3 H]lysine as substrate was 1·5 at 1 h, but by 4 h had fallen to 0·4, a ratio which was maintained for up to 8 days. A similar reversal occurred with phenylalanine as substrate. These changes were interpreted as evidence for the presence of a rapidly‐labelling protein fraction in the neurons which is subsequently transported out. Subcellular fractionation showed that over the 4 h period the rapidly labelling fraction was not transported to the synaptosomes. Incubation of prelabelled cortex slices followed by cell fractionation showed that a differential transport of protein of higher than average specific activity from both neurons and neuropil fractions occurred; there is a tendency for preformed highly labelled protein to accumulate during the in vitro incubation in Fraction D, a pellet enriched in red cells, some large neuronal perikarya and cell nuclei. When cell fractions were prepared after in vitro incubation, the distribution of the material down the gradient differed from that when fresh tissue was fractionated, as demonstrated by microscopic examination and the distribution of β‐galactosidase, a neuronal marker. Double‐label experiments showed that this redistribution could not account for the preferential loss and accumulation of prelabelled protein. It was noted that in vivo incorporation into the rapidly labelling neuronal protein is suppressed under certain changed environmental conditions, such as dark rearing. This is interpreted as lending support to the concept of the state‐dependence of neuronal and neuropil protein synthesis and their inter‐relations.