Table II.

The Reduced Binding Ability of the Tyrosine Mutants Correlates with Their Reduced Ability to Bind to MDCK.2 Cells

Etx-H149A mutant	Mean fold-change in CT50 relative to Etx-H149A	Mean fold-change in fluorescence intensity relative to P-Etx-H149A
Y30A	27.8 ± 7.3***	−20.7 ± 4.5***
Y196A	9.1 ± 2.1**	−6.0 ± 2.6**
Y36A	5.7 ± 2.6	−3.7 ± 1.5
Y29A	4.1 ± 2.2	−3.3 ± 0.6
Y16A	3.5 ± 2.9	−1.7 ± 0.6
Y20A	2.5 ± 1.3	−1.3 ± 0.6

The binding activity of each Tyr mutant was expressed as the fold-change in fluorescence intensity relative to P-Etx-H149A as determined in Figure 4. The cytotoxic activity of tyrosine mutants was expressed as the fold-change in CT₅₀ relative to Etx-H149A as determined in Figure 5(B). Statistically significant differences are indicated by asterisks.