UDP-alpha-D-xylose + an N-acylsphing-4-enine <=> a beta-D-xylosyl-(1<->1')-N-acylsphing-4-enine + UDP + H(+)
udp-alpha-d-xylose + an n-acylsphing-4-enine <=> a beta-d-xylosyl-(1<->1')-n-acylsphing-4-enine + udp + h(+)