Regulation of inorganic sulfate activation in filamentous fungi. Allosteric inhibition of ATP sulfurylase by 3'-phosphoadenosine-5'-phosphosulfate.

ATP sulfurylases from Penicillium chrysogenum, Penicillium duponti, Aspergillus nidulans, and Neurospora crassa are strongly inhibited by 3'-phosphoadenosine-5'-phosphosulfate (PAPS), the product of the second (adenosine-5'-phosphosulfate kinase-catalyzed) reaction in the two-step activation of inorganic sulfate. The v versus [PAPS] plots are sigmoidal. At physiological concentrations of MgATP (0.17-3 mM) and SO4(2-) (0.4-10 mM), the [I]0.5 for PAPS inhibition of the P. chrysogenum enzyme is 35-200 microM; [I]0.9 is 68-310 microM. In the presence of PAPS, the [S]0.5 values for both substrates are increased and the v versus [MgATP] and v versus [SO4(2-)] or [MoO4(2-)] plots are sigmoidal. Fluorosulfonate (FSO3-) and thiosulfate (S2O3(2-] (non-reactive sulfate analogs) inhibit the enzyme at subsaturating substrate concentrations in the absence of PAPS, but low concentrations of the analogs activate the enzyme when PAPS is present. Thus, PAPS behaves as an allosteric inhibitor of ATP sulfurylase. In contrast, adenosine-5'-phosphosulfate (APS = product Q), the immediate product of the SO4(2-)-dependent reaction, is a linear inhibitor of the P. chrysogenum enzyme, competitive with both MgATP and MoO4(2-) (Kiq = 36-73 nM). FSO3- or S2O3(2-) does not activate the enzyme in the presence of APS. The effect of PAPS on fungal ATP sulfurylase is very similar to that observed when a single highly reactive cysteinyl SH group/subunit (SH-1) is covalently modified (Renosto, F., Martin, R. L., and Segel, I. H. (1987) J. Biol. Chem. 262, 16279-16288). The results suggest that in vitro SH-1 modification induces a conformational change in the enzyme that mimics the change induced in vivo by the reversible binding of PAPS. No evidence was obtained to suggest that PAPS covalently modifies SH-1. ATP sulfurylases from rat liver (Yu, M., Martin, R. L., Jain, S., Chen, L. T., and Segel, I. H. (1989) Arch. Biochem. Biophys. 269, 156-174), spinach leaf, cabbage leaf, and Saccharomyces cerevisiae are not strongly inhibited by PAPS, do not display sigmoidal initial velocity plots in the presence of PAPS, and do not contain a highly reactive cysteinyl residue whose modification induces increased [S]0.5 values and sigmoidal velocity curves. The allosteric effect of PAPS on the fungal ATP sulfurylase may be part of a sequential feedback process unique to a group of organisms that use PAPS for two diverging pathways, reductive assimilation and sulfate ester formation.