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Senescent Cell Antigen 189

that the peptide was competing for the sulfate because increased amounts of sulfate overcame the inhibition (Hughes J, Haussler T, and Kay MMB, unpublished data).

1. Anion Binding/Transport Site Peptides were tested in an anion transport inhibition assay to determine which ones are involved in anion binding/transport (63). Peptides inhibited transport in a dose-dependent manner (63). Peptide residues 588-594 (a seven amino acid peptide), 822-839, and 869-883 were the most active inhibitors of anion transport (P ::; 0.001 compared to control without peptide) (Fig. 3) (Table 6). The inhibitory activity of the last peptide, 869-883, could not be confirmed by testing adjacent peptides to the amino side because these regions are extremely hydrophobic. However, six to seven amino acid peptides from this region produced inhibition of transport (63) but to a lesser degree than 869-883. The component residues are probably additive. Peptide 869-879 + 881 + 883 seem to have special anion binding/transport properties, although both it and 869-883 produced significant inhibition (P ::; 0.001).