Herpes simplex virus type 1 ribonucleotide reductase: selective and synergistic inactivation by A1110U and its iron complex

Abstract

2-Acetylpyridine-5-[(dimethylamino)thiocarbonyl]thiocarbonohydr azone (A1110U) inactivated herpes simplex virus Type 1 ribonucleotide reductase (EC 1.17.4.1) by a first-order process (kinact) which had a maximum value (Mkinact) of 8 hr-1 and a Kd that was less than 1 microM. The stable complex between iron and A1110U, (A1110U)2Fe+i, inactivated this enzyme with a Mkinact of 7 hr-1 and a Kd of 7 microM. Free A1110U and its iron-complex synergized as inactivators of the enzyme. For example, the kinact for the combination of 2 microM A1110U and 1 microM (A1110U)2Fe+i as independent inactivators was calculated to be about 9 hr-1, while the observed value was 32 hr-1. The bimolecular rate constant for inactivation of the viral enzyme by (A1110U)2Fe+i in the presence of a saturating concentration of A1110U was 2.5 10(7) M-1 hr-1 at 30 degrees. Human ribonucleotide reductase was less sensitive to the inhibitory effects of A1110U and its iron-complex. This enzyme was neither inhibited nor inactivated by A1110U and was weakly inhibited by (A1110U)2Fe+i. Furthermore, inactivation required the combination of A1110U and (A1110U)2Fe+i. The bimolecular rate constant for inactivation of human ribonucleotide reductase by (A1110U)2Fe+i in the presence of a saturating concentration of A1110U was considerably smaller (3.8 10(6) M-1 hr-1 at 37 degrees) than the analogous constant for the viral enzyme. Several iron-chelating reagents with unrelated structures substituted for free A1110U in its various roles with both enzymes. However, the iron complexes of these alternative chelators did not substitute for (A1110U)2Fe+i. The rates of inactivation of both enzymes were independent of the oxidation state of iron in (A1110U)2Fe+i and of CDP concentration. The inactivated enzymes were reactivated rapidly by FeSO4, but were not reactivated by CoCl2, CuSO4, or NiCl2. MnCl2 inhibited reactivation of the viral enzyme by FeSO4.