title: Properties of enzymes involved in D-galactonate catabolism in fungi.
abstract: Two enzymes catalyze the two step reactions in the D-galactonate nonphosphorolytic catabolic pathway of Aspergillus terreus, namely D-galactonate dehydratase and 2-keto-3-deoxy-D-galactonate (KDGal) aldolase. Maximum enzyme activities were obtained at 40 degrees C and pH 8.0 or at 50 degrees C and pH 7.5 for these two enzymes, respectively. Stability of the two enzymes under different conditions was investigated. From a Lineweaver-Burk plot of the reciprocal of initial velocities and substrate concentrations, apparent Km values were calculated for D-galactonate, pyruvate and glyceraldehyde and found to be 8.33, 14.28 and 5.55 mM, respectively, in crude cell-free extracts. Results indicated the requirement of magnesium cation for D-galactonate dehydratase activity at an initial concentrations of 10(-2) M. The presence of Mg2+ in the reaction mixture seems to induce greatly the fitness of the dehydratase with D-galactonate as no activity could be detected with 24-h dialyzed extract in the absence of magnesium cation.
authors.affiliation: Department of Microbial Chemistry, National Research Centre, Dokki, Cairo, Egypt.
authors.forename: A M
authors.initials: AM
authors.lastname: Elshafei
authors.forename: S M
authors.initials: SM
authors.lastname: Mohawed
authors.forename: M S
authors.initials: MS
authors.lastname: Ammar
authors.forename: O M
authors.initials: OM
authors.lastname: Abdel-Fatah
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism*; D001230:Aspergillus / Q000201:enzymology*; D003837:Deoxy Sugars / Q000378:metabolism; D004795:Enzyme Stability; D005985:Glyceraldehyde / Q000378:metabolism; D006836:Hydro-Lyases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007661:Ketoses / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D011489:Protein Denaturation; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D013400:Sugar Acids / Q000378:metabolism*; D013696:Temperature
chemical_list: D003837:Deoxy Sugars; D007661:Ketoses; D011773:Pyruvates; D013400:Sugar Acids; C012991:galactonic acid; D005985:Glyceraldehyde; D019289:Pyruvic Acid; C093801:2-keto-3-deoxy-D-galactonate aldolase; D000446:Aldehyde-Lyases; D006836:Hydro-Lyases; C019607:galactonate dehydratase; D008274:Magnesium