TABLE 1.

Amino acids recovered from acid elutions^a

Cycle	Yield (pmol) of:
	UL18	H-2Kd-hβ2m	FcRn	m144-hβ2m	m144-mβ2mb
1	86	84.5	5.9	13.7	7.3
2	75.1c	51.1d	4.7	0	1.5
3	36.9e	33.6	0.7	0.5	0.3
4	19.8	12.3	7.6	1.2	0.3
5	11.3	18.2	0	0.7	0.2
6	4.0	30.8	0	1.0	0.1
7	3.7	1.1	0.2	1.6	0.1
8	6.5	3.1	0.6	2.0	1.6
9	4.3	12.1	9.5	0.2	0.3
10	1.3	7.5	0.3	0.1	1.2
11	0.4	10.1	0.5	0.3	0.2
12	2.5	6.7	0.8	0.1	0.5

^aThe total yield of amino acids from each sequencing cycle is presented for acid eluates derived from equivalent amounts of soluble U_L18, K^d-hβ2m, FcRn, m144-hβ2m, and m144-mβ2m heterodimers. Only those amino acid residues that showed an increase in the absolute amount recovered compared to the previous cycle were considered significant. Results for the FcRn, K^d, and U_L18 eluates are similar to those previously reported (11, 37) in which soluble U_L18 and K^d, but not FcRn, were shown to bind endogenous peptides. 

^bAcid elution contributions from Asp, Glu, and Gly were not included in the m144-mβ2m tabulation because the first four cycles showed unusually high yields that were also present in the negative control. 

^cLeu, Met = 71. 

^dTyr = 25. 

^ePro = 19.