initiating step of pyranoside-to-furanoside conversion, did not give the corresponding Api product. Kinetic isotope effects (KIEs) support an UAXS mechanism in which substrate oxidation by enzyme-NAD+ and retro-aldol sugar ring-opening occur coupled in a single rate-limiting step leading to decarboxylation. Rearrangement and ring-contracting aldol addition in an open-chain intermediate then give the UDP-Api
C分支糖d-apiose(Api)对植物细胞壁发育至关重要。酶催化的脱羧/
吡喃糖苷环收缩反应从
UDP-α-d-
葡萄糖醛酸(
UDP-GlcA)到Api前体
UDP-α-d-apiose(
UDP-Api)。我们检查了具有站点选择性2 H标记和脱氧底物的
UDP-Api /
UDP-α-d-
木糖合酶(UAXS)的机制。防止C-2 / C-3羟醛裂解的类似的
UDP-2-脱氧-GlcA类似物,可能是
吡喃糖苷向
呋喃糖苷转化的起始步骤,但未提供相应的Api产物。动力学同位素效应(KIE)支持UAXS机制,其中通过酶
NAD +和逆醛醇糖开环发生的底物氧化发生在导致脱羧的单个限速步骤中。