Purification and biochemical characterization of a β-cyanoalanine synthase expressed in germinating seeds of Sorghum bicolor (L.) moench

Abstract

Background: β-Cyanoalanine synthase plays essential roles in germinating seeds, such as in cyanide homeostasis. Methods: β-Cyanoalanine synthase was isolated from sorghum seeds, purified using chromatographic techniques and its biochemical and catalytic properties were determined. Results: The purified enzyme had a yield of 61.74% and specific activity of 577.50 nmol H2S/min/mg of protein. The apparent and subunit molecular weight for purified β-cyanoalanine synthase were 58.26 ± 2.41 kDa and 63.4 kDa, respectively. The kinetic parameters with sodium cyanide as substrate were 0.67 ± 0.08 mM, 17.60 ± 0.50 nmol H2S/mL/min, 2.97 × 10−1 s−1 and 4.43 × 102 M−1 s−1 for KM, Vmax, kcat and kcat/KM, respectively. With L-cysteine as substrate, the kinetic parameters were 2.64 ± 0.37 mM, 63.41 ± 4.04 nmol H2S/mL/min, 10.71 × 10−1 s−1 and 4.06 × 102 M−1 s−1 for KM, Vmax, kcat and kcat/KM, respectively. The optimum temperature and pH for activity were 35°C and 8.5, respectively. The enzyme retained more than half of its activity at 40°C. Inhibitors such as HgCl2, EDTA, glycine and iodoacetamide reduced enzyme activity. Conclusion: The biochemical properties of β-cyanoalanine synthase in germinating sorghum seeds highlights its roles in maintaining cyanide homeostasis