Table I.

Accurate mass determination indicates multiple phosphorylation of recombinant OST1

ESI-LC-TOF mass measurements for 10xHis-OST1 and mutant version 10xHis-OST1G33R. The third column indicates the experimental average mass of the various isoforms found in each sample. The fourth one indicates for each isoform the calculated number of phosphate groups based on the difference between experimental and theoretical masses (79.96 D per phosphate group).

Recombinant ProteinTheoretical MassExperimental MassesCalculated No. of Phosphate Groups
DD
10xHis-OST146,34246,658 ± 64
46,740 ± 55
46,820 ± 86
46,899 ± 47
46,978 ± 58
47,060 ± 59
47,151 ± 710
10xHis-G33R46,44240,299 ± 7xa
46,436 ± 80
  • a This isoform does not correspond to a full-length protein.