UDP-L-arabinose mutase involved in the biosynthesis of cell wall non-cellulosic polysaccharides. Catalyzes the interconvertion of UDP-L-arabinopyranose (UDP-Arap) and UDP-L-arabinofuranose (UDP-Araf). Preferentially catalyzes the formation of UDP-Arap from UDP-Araf. At thermodynamic equilibrium in vitro the ratio of the pyranose form over the furanose form is 90:10. Is probably active as heteromer in vivo. UDP-beta-L-arabinofuranose = UDP-beta-L-arabinopyranose Optimum pH is 5.5-6.0. Heteromers with UAM2 and UAM3. The conserved DXD motif is involved in enzyme activity. Reversibly glycosylated in vitro at Arg-158 by UDP-glucose. Reversibly glycosylated by UDP-xylose and UDP-galactose. Belongs to the RGP family. Truncated N-terminus.