xanthosine + phosphate <=> alpha-D-ribose 1-phosphate + xanthine
xanthosine + phosphate <=> alpha-d-ribose 1-phosphate + xanthine
xanthosine + phosphate <=> alpha-D-ribose 1-phosphate + xanthine
xanthosine + phosphate <=> alpha-d-ribose 1-phosphate + xanthine