Further in vitro studies on the biochemistry of the inhibition of nucleic acid and protein synthesis induced by arsenic.

Human lymphocytes, stimulated by PHA, and exposed to increasing Na2HAsO4 concentrations, show an identical incorporation rate for 14C thymidine and 14C-TTP into the DNA. 14C uridine is incorporated 3--4 per cent less at an As concentration of 1.0 mug/ml medium, above this however approximately 15 per cent less into the RNA as compared to 14C-UTP. In free pyrimidine bases, the incorporation of labelled triphosphates into the DNA and RNA is significantly reduced above 1 mug and 10 mug Na2HAsO4. Corresponding to its approximately uniform distribution into DNA and RNA, the incorporation rate of 14C-ATP above 10 mug Na2HAsO4/ml culture medium lies between that of 14C-UTP and 14C-TTP. The incorporation of 14C alanine and 14C leucine into cellular protein is not reduced below 10 mug Na2HAsO4/ml. The incorporation rate is 41 per cent at a concentration of 100 mug Na2HAsO4/ml medium. Compared to 14C-UTP, 14C-ATP and 14C-TTP it is increased by the factor of 1.8; 2.5 and 6.8 respectively. The inhibition of enzymes of the dark repair mechanisms and the synthesis of biopolymers together with their altered sequence and the involvement of long-lived messenger RNA serve as an explanation of the observed alterations of the lymphocyte metabolism, caused by arsenic.