Effect of water-soluble zinc porphyrin on the catalytic activity of fumarase for l-malate dehydration to fumarate

Abstract

Fumarase from porcine heart (FUM; EC 4.2.1.2) is an enzyme that dehydrates L-malate in an aqueous medium to catalyze fumarate production. In the visible-light driven NADH regeneration with the system of an electron donor, water-soluble zinc porphyrin as a photosensitizer and pentamethylcyclopentadienyl rhodium 2,2′-bipyridine complex ([Cp*Rh(bpy)(H₂O)]²⁺) and malate dehydrogenase from Sulfobus tokodaii (oxaloacetate-decarboxylating; MDH; EC 1.1.1.38), fumarate can be produced from CO₂ and pyruvate by dehydrating L-malate produced as an intermediate with FUM. To improve fumarate production efficiency in this system, it is necessary to study the interaction between FUM and water-soluble zinc porphyrin. In this work, the effect of water-soluble zinc or metal-free porphyrin derivatives, tetra(4-sulfonatophenyl)porphyrin, tetra(4-carboxyphenyl)porphyrin, tetrakis(4-methylpyridyl)porphyrin or tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin on the catalytic activity of FUM for L-malate dehydration to fumarate was studied. It was found that the addition of anionic water-soluble zinc porphyrins, zinc tetra(4-sulfonatophenyl)porphyrin (ZnTPPS⁴⁻) and zinc tetra(4-carboxyphenyl)porphyrin (ZnTCPP⁴⁻) inhibited the catalytic activity of FUM. In particular, fumarate production with FUM was strongly suppressed in the addition of ZnTPPS⁴⁻ (reduced to about 16% compared to control experiments). On the other hand, the addition of cationic water-soluble zinc or metal-free porphyrins had little effect on the catalytic activity of FUM for L-malate dehydration to fumarate. Furthermore, UV-vis absorption and circular dichroism spectroscopic results suggested that ZnTPPS⁴⁻ binds to the substrate-binding site of FUM and inhibits fumarate production.