Table VI.

pH dependence of the spontaneous in vitro condensation of cyclo-Dopa with BA as shown by betanidin formation at five different pH values

pH 6.2	pH 5.3	pH 4.5	pH 3.8	pH 3.1
nmol min−1
0.01	0.15	0.26	0.32	0.42

BA (5 nmol) was added to cyclo-Dopa (40 nmol) in 0.1 m citrate/0.2 m NaPi-buffer (pH 3.0–6.5, containing 10 mm ascorbate). The kinetics of the A₅₄₀ increase was monitored photometrically for 10 min. The betanidin formation (nmol min⁻¹) was calculated from the linear parts of the progress curves at different pHs. Each value is the average of duplicate samples.