Table 2.

Summary of Products from Proteolysis of Aec- or Mac-Modified Synthetic α-S1 Casein Phosphopeptides 106–119 Including Substitutions at Asn-114 or pSer-115

modified α-S1 casein peptides & cleavage products	trypsin proteolysis % peptidea	Lys-C proteolysis % peptidea
VPQLEIVPN(Aec)AEERb	74.1 ± 0.8	67.5 ± 1.6
α106–115/VPQLEIVPN(Aec)	4.1 ± 2.0	28.9 ± 1.4
α106–114/VPQLEIVPN	21.8 ± 1.8	2.6 ± 0.3
VPQLEIVPA(Aec)AEER	54.9 ± 2.1	75.5 ± 0.6
α106–115/VPQLEIVPA(Aec)	41.2 ± 2.7	21.8 ± 0.5
α106–114/VPQLEIVPA	2.8 ± 0.7	2.7 ± 0.2
VPQLEIVPN(Mac)AEER	88.8 ± 0.4	97.2 ± 0.2
α106–115/VPQLEIVPN(Mac)	n.d.c	n.d.
α106–114/VPQLEIVPN	11.2 ± 0.4	2.8 ± 0.2
VPQLEIVPNKAEER	24.5 ± 1.3	n.d.
α106–115/VPQLEIVPNK	60.3 ± 6.6	100
α 106–114/VPQLEIVPN	15.3 ± 7.6	n.d.
VPQLEIVPNpYAEER	100	100
α106–115/VPQLEIVPNpY	n.d.	n.d.
α106–114/VPQLEIVPN	n.d.	n.d.

^aAmount of peptide products are expressed as a relative percentage of peptide cleavage ± the standard deviation from two independent experiments. Percentages ≤ 3.0% are background noise in the spectrum.

^bAbbreviations are as follows: Aec, S-2-aminoethylcysteine; Mac, β-methlyamino-ethylcysteine; pY, phosphotyrosine.

^cn.d.= product not detected.