- SAMP+GDP+Pi (7) 1963).
Coli has been extensively studied. It appears that here are two catalytic subnits and four regulatory subunits per molecule of the native enzyme. Since the catalytic subunits are structurally different from the regulatory subunits, the catalytically active sites are likely to be distinct from the allosteric binding sites where the effector molecules interact. Another allosteric control by which the level of deoxyribonucleotides for DNA synthesis is maintained appears to be of considerable interest.
Subsequently it was shown that ara-A is effective in inhibiting the growth of a number of ascites tumors in mice and of mouse fibroblasts in suspended cell culture (BRINK and LEPAGE, 1964; BRINK and LEPAGE, 1964 a; BRINK and LEPAGE, 1965; DOERING, KELLER and COHEN, 1966). Its effectiveness in producing breaks in the chromosomes of human leukocytes induced to divide by phytohemaglutinin has been reported (NICHOLS, 1964). The antitumor effect of the analogue is decreased by its enzymatic deamination in vivo and the biologically inactive catabolite, arabinosylhypoxanthine is rapidly excreted (LEPAGE and JUNGA, 1965).