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Adenosine 5'-Triphosphate-Sulfurylase in Corn Roots and Its Partial Purification ¹

^a Department of Agronomy and Agricultural Research Service, United States Department of Agriculture and Department of Botany and Plant Pathology, Colorado State University, Fort Collins, Colorado 80521

ATP-sulfurylase (ATP-sulfate adenyltransferase, EC 2.7.7.4) was found in nonparticulate fractions of both roots and leaves of Zea mays L. seedlings using two detection methods. Addition of exogenous pyrophosphatase was essential for maximum rates of conversion of ³⁵SO₄^2– to labeled adenosine phosphosulfate in unpurified root extracts, but not in unpurified leaf extracts. In the presence of exogenous pyrophosphatase, the enzyme from roots exhibited specific activities as high as those obtained with the leaf enzyme. The root enzyme was purified 33-fold by centrifugation and column chromatography procedures. Its molecular weight obtained by Sephadex gel filtration was about 42,000. Its Km for pyrophosphate was 7 µM, while for adenosine phosphosulfate, the Km was 1.35 µM. None of the enzyme fractions studied converted adenosine phosphosulfate into detectable amounts of 3'-phosphoadenosine-5'-phosphosulfate. ATP-sulfurylase was also found in roots of corn seedlings grown aseptically. The data suggest that at least the first reaction in sulfate reduction might proceed as effectively in roots as in shoots.

¹ Contribution from Colorado State University Experiment Station and Agricultural Research Service, United States Department of Agriculture. This work was supported in part by the International Atomic Energy Agency. Published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series No. 1786.

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