Abstract
The gene encoding 5′-adenylylsulfate (APS) kinase (EC 2.7.1.25) (APK) was cloned fromArabidopsis thaliana.There is a singleAPKlocus inA. thaliana.The coding sequence of the gene is composed of 7 exons, interrupted by 6 introns. A transcriptional initiation site was detected 120 bp 5′ of the initiation codon.APKmRNA is slightly more abundant in leaves than in roots ofA. thalianaand its level does not change in response to sulfur starvation. TheAPKprotein, synthesized in vitro, is able to enter isolated intact chloroplasts. Recombinant APS kinase shows maximal activity at 10 μM APS with 5 mM ATP, but it is inhibited at APS concentrations above 10 μM. The inhibition is alleviated at higher ATP concentrations. Reciprocal plot analysis showed that the theoretical Vmaxis ∼1.2 μmol min−1mg−1at 25°C, pH 8.0; the Kmvalues are 3.6 μM APS and 1.8 mM ATP.
Published Version
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