Table 4.

Site of phosphorylation identified in OATP1B1 by LC-MS/MS. Mascot score, phosphoRS probability, ion mass and peptide mass accuracy were shown for representative phosphopeptides. Results from two independent experiments (n=2) are shown.

Phosphorylation Site	Mascot Scorea	PhosphoRS Probabilityb	Ion Mass (Da)	Peptide Mass Accuracy (ppm)c
S293	147.53	99.95%	2933.4184	1.8
S295	62.56	99.99%	3013.3798	0.1
T301	29.22	99.33%	2933.4131	1.5
T439	81.98	33.33%	2114.9113	1.0
T441	81.98	33.33%	2114.9113	1.0
Y442	81.98	33.33%	2114.9113	1.0
Y590	36.59	99.99%	2229.1441	−3.5
S659	105.34	100.00%	2424.9364	−1.2
S663	105.34	100.00%	2424.9364	−1.2

^aThe Mascot score is expressed as −10*LOG₁₀(P), where P is the absolute probability that the observed match is a random event. Mascot scores greater than 67 are significant (p<0.05), suggesting that the null hypothesis that observed match is a random event had a probability of less than 5%⁸⁴.

^bphosphoRS probability

^cPeptide mass accuracy= 10⁶

^*(M_i-M_a)/M_a in ppm, where M_i and M_a are the observed and calculated mass, respectively, in Da⁸⁵. The absolute mass accuracy value of less than 4 indicates accurate peptide assignments