Incorporation of radioactive phosphate into the nucleic acids of brain slices.
The unequivocal incorporation of radioactive phosphate (32p) into the nucleic acids of brain slices has not as yet been demonstrated. Because of the great interest in the nucleic acids of the nervous system aroused by the work of Caspersson (1947) and Hyden (1943, 1947), it was decided to investigate the possible incorporation of 32p into the pentosenucleic acid (PNA) and deoxypentosenucleic acid (DNA) of slices of brain tissue respiring in a suitable oxygenated medium. In experiments with tissue slices only a small amount of material is available. For this reason most previous workers carrying out in vitro experiments have resorted to the method of Schmidt & Thannhauser (1945) for the separation of PNA and DNA. It has been shown by Jeener (1949), Davidson, Frazer & Hutchinson (1951), Szafarz & Paternotte (1951), and others, in experiments in which animals were killed after the administration of 82p, that the specific activity of the Schmidt-Thannhauser PNA fraction of liver is much greater than that of more purified PNA preparations from the same tissue, even after the very active orthophosphate fraction, presumably derived from 'phosphoprotein', has been removed. Strickland (1952) reported similar findings for brain tissue. With tissue from the nervous system the situation is even less favourable than with liver, for Logan, Mannall & Rossiter (1952) have shown that more than one-half of the protein-bound phosphorus of brain tissue appears in the Schmidt-Thannhauser hydrolysate in the form of organic phosphate that has not the characteristic ultraviolet absorption of nucleotides. In white matter of brain this non-nucleotide phosphorus, which has a specific activity much greater than that ofPNA, may account for as much as 80% of the phosphorus in the Schmidt-Thannhauser PNA fraction. Much of this phosphorus may be derived from the inositol-containing complex isolated from brain by Folch & Le Baron (1951), but other active phosphorus compounds may be present also. Davidson & Smellie (1952b) have recently shown that the Schmidt-Thannhauser PNA fraction ofrat-liver tissue contains at least six non-nucleotide phosphate derivatives, which together make up 25 % of the phosphorus of the fraction. Two hours * Ontario Research Council Scholar.