Table 2. Direct Identification and Calculation of Phosphosite Occupancy for Prohormone-Derived Peptides.

Summary of phosphosite occupancies for known endogenous peptides, calculated by comparison of phosphopeptide intensity with intensity of its non-phosphorylated counterpart. Bold and underlined residues indicate a localized residue (AScore > 13). Multiple entries for the same sequences are due to multiple, distinct phosphopeptides. Lowercase “m” indicates oxidized methionine.

Name	Sequence	Gene	Localized*	Occupancy (%)
C-terminal peptide	SVPHFSDEDKDPE	SCG5	√	98.7
Enkelytin	FAEPLPSEEEGESYSKEVPEmEKRYGGFm	PENK		77.0
Enkelytin	FAEPLPSEEEGESYSKEVPEmEKRYGGFm	PENK		10.3
VIF	HSSYEDELSEVLEKPNDQAEPKEVTEEVSSKDAAE	CHGA		4.7
P01211(192–203)	SPHLEDETKELQ	PENK	√	0.3
Secretolytin	QKIAEKFSGTRRG	CHGB		0.1
P01211(192–203)	SPHLEDETKELQ	PENK	√	0.02

^*Refers to phosphosite localization on intact peptide sequence—localization may have been achieved on related extensions and fragments. Peptide phosphosite occupancy was determined by the direct method of LC-MS/MS.