Galacto kinase ec 188.8.131.52 of vicia faba seeds
European Journal of Biochemistry 136(1): 155-160
ISSN/ISBN: 0014-2956 Accession: 005500223
Galactokinase (EC 184.108.40.206) from the dormant seeds of V. faba was purified approximately 1300-fold with an 18% recovery through an 8-step procedure. The preparation showed the presence of only minor contaminations as judged by disc-gel electrophoresis. The native enzyme displayed a MW of approximately 60,000 (determined by Sephadex G-100 gel-filtration) and the subunit value was 30,000. The isoelectric point of the enzyme was 5.3 and the amino acid analysis showed high percentage of acidic amino acids. The pH optimum of the enzyme was 7.3 at 25.degree. C. The relative activity for phosphorylating various monosaccharides followed the order, D-galactose > 2-deoxy-D-galactose > D-galactosamine; D-fucose, L-arabinose, L-galactose and D-glucose were not phosphorylated. Whereas ATP acted as an efficient phosphate donor, ADP, GTP and UTP were unable to act in this capacity. The Km and the V values of the substrates were determined. The metal ion requirement for the enzymic activity followed the order, Mg2+ > CO2+ > Mn2+ > Ni2+ > Ca2+. The enzymic reaction was inhibited by heavy metal ions and sulfhydryl reagents indicating the participation of -SH group(s) in enzymic catalysis. Production inhibitoin was observed; galactose 1-phosphate and ADP were competitive and non-competitive inhibitors, respectively. Seed germination showed an increase in galactokinase level up to 24 h followed by a rapid decrease. The level of raffinose and stachyose decreased continually. The galactokinase level was sufficiently high to phosphorylate the liberated galactose. No free galactose was observed at any stage of germination.