Figure 6.

Maize Profilins Inhibit Nucleotide Exchange on Pollen Actin.

(A) The incorporation of ε-ATP by 0.5 μM pollen actin in the absence (curve at center) or presence of 0.1 μM human profilin I (curve at top) or 0.5 μM ZmPRO5 (curve at bottom) was monitored over time. Human profilin I dramatically enhances the initial nucleotide exchange rate, whereas ZmPRO5 inhibits the rate slightly.

(B) The rate of incorporation of ε-ATP () was determined by fitting the data with a single exponential function as shown in (A). For several experiments, the average rate for actin alone was 0.059 ± 0.0045 (; column 1). The average rates in the presence of 0.1 μM human profilin I, 0.5 μM DNase I, 0.5 μM ZmPRO1, 0.5 μM ZmPRO5, or 0.5 μM native pollen profilin were 0.18 ± 0.035 (), 0.025 ± 0.0048 (), 0.043 ± 0.0032 (), 0.036 ± 0.0052 (), and 0.043 ± 0.0058 (), respectively. The rate of ε-ATP incorporation by pollen actin alone was significantly different by the two-tailed t test from incorporation of ε-ATP by pollen actin in the presence of the profilins or DNase I (). Error bars represent sd.