Enzymatic conversion of D-glucose to D-fructose.

days against EDTA. Assuming a molecular weight for the virus of 50 x 106, calculation of the number of atoms of iron, copper, calcium, and magnesium per virus particle gave values of 20, 3, 52, and 45, respectively. The fact that iron and magnesium were concentrated approximately 20-fold in the virus ribonucleic acid compared with the occurrence of about 5 percent nucleic acid in the virus indicates that these metals are located in the nucleic acid rather than in the protein. That their occurrence in the virus nucleic acid in the concentrations found may be of more general significance in relation to nucleic acid chemistry is indicated by the comparable amounts found in yeast ribonucleic acid. The relatively strong binding of the virus ribonucleic acid for iron and magnesium as shown by the dialysis experiments against EDTA (5) indicates the existence of metal chelates or relatively stable metal complexes in ribonucleic acid structure. While the function of the individual metals in the virus or in its nucleic acid is not clear at present, some of them may be involved in the binding of smaller nucleic acid subunits into the larger asymmetric particles characteristic of "native" and infectious nucleic acid (14). Since the tobacco mosaic virus undergoes a disintegration into relatively small units soon after inoculation (15), it appears that the larger nucleic acid may undergo a subdivision into smaller genetic subunits during the infection process in a manner similar to that shown for bacteriophage by Doermann (16) and by Visconti and Delbruck (17). A further logical hypothesis is that the genetic subunits, the "vegetative phase" of Visconti and Delbriick, are joined into the larger asymmetric particles, the "genetic recombinants" characteristic of "native" and infectious ribonucleic acid by metal chelate bonds. Although no analyses for the metallic components considered in this paper have yet been made on "native" deoxyribonucleic acid, it is known that magnesium is present (11). The occurrence of smaller deoxyribonucletic acid units joined by metal chelate bonds into the highly asymmetric particles characteristic of "native" deoxyribonucleic acid would appear to provide a rational explanation for many of the physical (18) and biological (19) properties of this nucleic acid also (20). HUBERT S. LORING RICHARD S. WARITZ* Department of Chemistry, and School of Medicine, Stanford University, Stanford, California