Faculty Collaboration Database

Adenosinetriphosphate sulfurylase from Penicillium chrysogenum: steady-state kinetics of the forward and reverse reactions, alternative substrate kinetics, and equilibrium binding studies. Arch Biochem Biophys 1985 Aug 01;240(2):509-23

Date

08/01/1985

Pubmed ID

2992379

DOI

10.1016/0003-9861(85)90057-8

Scopus ID

2-s2.0-0022258155 (requires institutional sign-in at Scopus site)   38 Citations

Abstract

The kinetics of the forward ATP sulfurylase-catalyzed reaction were examined using a new assay based on 32PPi released from [gamma-32P]MgATP in the presence of inorganic sulfate. Replots yielded Vmaxf = 6.6 units mg protein-1, KmA = 0.13 mM, Kia = 0.33 mM, and KmB = 0.55 mM, where A = MgATP and B = SO2-4. Thiosulfate, a dead-end inhibitor of the reaction, was competitive with sulfate and noncompetitive with respect to MgATP. The ratio kcat/KmA was determined for several alternative inorganic substrates, B, where A = MgATP and B = SO2-4, SeO2-4, MoO2-4, WO2-4, or CrO2-4. For SO2-4 and SeO2-4, the ratio was 5-6.5 X 10(4) M-1 S-1; for the others, the ratio was 5.8-7.3 X 10(5) M-1 S-1. The results support a random addition of MgATP and inorganic substrate. The kinetics of the reverse reaction were examined using a new assay based on 35SO2-4 release from [35S]APS (adenosine 5'-phosphosulfate) in the presence of MgPPi. Reciprocal plots were linear, intersecting below the horizontal axis. Replots yielded Vmaxr = 50 units mg protein-1, KmQ = 0.3 microM, Kiq = 0.04 microM, and KmP = 4 microM, where Q = APS and P = PPi (total of all species). MgATP and SO2-4 were both competitive with APS and noncompetitive with respect to MgPPi. Taken together with earlier results suggesting that APS is competitive with both MgATP and SO2-4 and that MgPPi is noncompetitive with respect to both substrates, the qualitative results point to a random A-B, ordered P-Q kinetic mechanism. The Scatchard plot for [35S]APS binding was curved, indicating either negative cooperativity or more than a single class of sites. [gamma-32P]MgATP displayed half-site saturation in the presence of saturating FSO-3.

Author List

Seubert PA, Renosto F, Knudson P, Segel IH

Author

Paul Knudson MD Associate Professor in the Medicine department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Adenosine Triphosphate
Binding, Competitive
Fluorides
Kinetics
Mathematics
Nucleotidyltransferases
Penicillium
Sulfate Adenylyltransferase
Sulfuric Acids