Table 3.

Competition of Basic Residues When Two Are Present^a

tracking	contain	exclude	count	correlation	slope
R	H, R	K	180	0.826	0.920
H	H, R	K	180	−0.098	−0.105
R	K, R	H	275	0.873	1.171
K	K, R	H	275	−0.171	−0.252
H	H, K	R	98	0.462	0.456
K	H, K	R	98	0.256	0.266

^aEach set was analyzed twice, once for each base. The “tracking” column indicates which of the two basic residues' positions was used for the linear regression in each row. When arginine was present, its effect was far more pronounced than the other basic residue (as evidenced by arginine’s higher slopes and correlations in the first and second sets). Histidine and lysine positions are positively correlated with series intensity when they are the only basic residues in the peptide (see Table 2), but the presence of arginine changes this correspondence to a negative correlation. When histidine and lysine are the only basic residues in a peptide, histidine produces the higher slope and correlation.