TABLE 1.

Tandem mass spectrometry identification of phosphorylation sites on Na,K-ATPase α1 subunit in rat parotid acinar cells

Samples were obtained prepared using α1-immunopreciptations followed by proteolysis and LC/MS/MS analyses. Shown are conditions for which each site was identified and putative kinases that are known or predicted to phosphorylate specific sites. The abbreviations used are: CK2, casein kinase 2; IR, insulin receptor; IGF1R, IGF1 receptor; ATMK, ataxia telangiectasia mutated kinase; B, basal; I, isoproterenol; C, carbachol; CA, calyculin A; P, PMA; pool, B+C+I combined; Charge, charge state of peptide ion; Δmass, difference between experimental peptide mass and known sequence; Sf, Sequest final score; MH+, protonated molecular mass; Xcorr, Sequest cross-correlation score; ΔCn, Xcorr difference between the top ranked and next best sequence; Sp, Sequest preliminary score; rank, top hit from protein database. Accession number was AAB81285 for all sequences. All sequences were ranked No. 1 as the top hit from the protein database.

Sequence	Site	Charge	Δmass	Sf	MH+	Xcorr	ΔCn	Sp	Condition detected	Kinase
			ppm
YEPAAVpSEHGDKK	Ser-16	2	−2.0	0.93	1511	3.98	0.41	744	P + CA, pool	PKC
YEPAAVSEHGDKKpSK	Ser-23	2	−0.4	0.92	1726	3.94	0.63	389	P + CA	PKC
VDNSpSLTGESEPQTR	Ser-217	2	−1.5	0.9	1700	4.31	0.05	1004	B, C, I, P	CK2
VDNSSLTGEpSEPQTR	Ser-222	2	−2.2	0.86	1700	3.68	0.01	1114	B, pool	CK2
GIVVpYTGDR	Tyr-260	2	−1.3	0.84	1060	2.22	0.24	999	Pool	IR, IGF1R
DNQIHEADTTENQpSGVSFDK	Ser-407	3	0.3	0.77	2315	3.16	0.19	922	Pool
EVSMDDHKLpSLDELHR	Ser-47	3	1.9	0.55	2004	2.81	0.32	270	C, P + CA	ATMK,PKA