Protein bound radioactivity in neuronal and glial fractions following intra-carotid 3H-leucine perfusion.

Brain proteins in one cerebral hemisphere were labeled by means of intracarotid perfusion with 3H-leucine by a 40 s pulse. Recirculating precursor contributed little to the protein bound radioactivity. This radioactivity reached a peak level 30 min after perfusion. Fractions enriched in neuronal perikarya and glial cells showed a similar time course of labeling, but the neuronal fraction demonstrated the highest level of protein bound radioactivity. Subcellular fractions from whole brain were studied by the same system. The highest protein bound radioactivity was observed in the nuclear and microsomal fractions. The brain entry of the precursor by means of a controlled intracarotid pulse of short duration offers particular advantages in short-term experiments since the systemic metabolism of the labeled precursor is largely avoided. The easily achieved high labeling of proteins facilitates assay of the radio-activities in different cellular and subcellular fractions and also allows analyses of relative turnover rates in electrophoretically separated proteins.