A Chromatographic Comparison of Protein Displaying Deoxyribonucleic Acid Ligase Activity Extracted from Nuclei of BHK-21/C13 Cells Before and After Infection with Herpes Simplex Virus Type I

1.4 respectively. Thus the increase in activity reported by Tomozawa & Wolfenden (1970) on reaction of 6mol of thiol groups/mol of enzyme withp-mercuribenzoate and found again in the present work with 5,5’-dithiobis-(2-nitrobenzoate) results from an increased activation by univalent cations. The effects of the modification of enzyme thiol groups on the response to nucleotide modifiers was also studied. At 1 mM ATP and A D P activate whereas G T P inhibits A M P deaminase (Tomozawa & Wolfenden, 1970). G T P inhibition is decreased by 28 % in the 5,5’-dithiobis-(2-nitrobenzoate)-treated enzyme. Activation by ATP and A D P is unaffected. The addition of G T P during the reaction of 5,5’-dithiobis-(2-nitrobenzoate) with the enzyme does not alter the number of mol of thiol groups/mol reacting o r the changes in activity that accompany the reaction. Thus the decrease in G T P inhibition appears to result from a structural modification associated with the reaction of 6mol of thiol groups/mol with 5,5’-dithiobis-(2-nitrobenzoate) rather than from the modification of thiol groups at GTP-binding sites. The lack of effect of reaction of N-ethylmaleimide with the enzyme not only on activation by ATP and A D P but also on inhibition by G T P supports this.