Purification and Properties of Acyl Coenzyme A Thioesterase II from Rhodopseudomonas sphaeroides

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A high molecular weight acyl coenzyme A (acyl-CoA) thioesterase, designated thioesterase II, has been purified 5300-fold from photoheterotrophically grown cells of Rhodopseudomonas sphaeroides. In contrast to R. sphaeroides acyl-CoA thioesterase I [Boyce, S. G., & Lueking, D. R. (1984) Biochemistry 23, 141–147], thioesterase II has a native molecular mass (Mr) of 120000, is capable of hydrolyzing saturated and unsaturated acyl-CoA substrates with acyl chain lengths ranging from C4 to C18, and is completely insensitive to the serine esterase inhibitor diisopropyl fluorophosphate. Palmitoyl-CoA and stearoyl-CoA are the preferred (lowest km) saturated acyl-CoA substrates and vaccenoyl-CoA is the preferred unsaturated substrate. However, comparable Vmax values were obtained with a variety of acyl-CoA substrates. Unlike a similar thioesterase present in cells of Escherichia coli [Bonner, W. M., & Bloch, K. (1972) J. Biol. Chem. 247, 3123–3133], R. sphaeroides thioesterase II displays a high ratio of decanoyl-CoA to palmitoyl-CoA activities and exhibits little ability to hydrolyze 3-hydroxyacyl-CoA substrates. Only 3-hydroxydodecanoyl-CoA supported a measureable rate of enzyme activity. With the purification of thioesterase II, the enzymes responsible for > 90% of the acyl-CoA thioesterase activity present in cell-free extracts of R. sphaeroides have now been identified. © 1986, American Chemical Society. All rights reserved.

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