title: Side chain reactivities of glucoamylase G2 from Aspergillus niger evaluated by group-specific chemical modifications.
abstract: Treatment of glucoamylase G2 with large excesses of different group specific reagents resulted in modification of 25% of the histidyl, 15% of the tyrosyl, 20-40% of the arginyl, 30-50% of the lysyl and none of the methionyl residues. The modified groups were not critical since the various derivatives possessed from 50% to 100% residual enzymatic activity and retained the thermostability. Carboxamidomethylation occurred specifically at His254 with essentially no change of the kinetic parameters for hydrolysis of maltose and starch. Removal of the two N-linked sugar units by endoglycosidase H was similarly without effect on activity, thermostability and chemical reactivity of the histidyl residues. H(+)-titration revealed that glucoamylase G2 carries a lower net charge throughout the pH-range 3-11 than predicted from its amino acid composition.
authors.affiliation: Department of Chemistry, Carlsberg Laboratory, Copenhagen Valby.
authors.forename: K
authors.initials: K
authors.lastname: Håkansson
authors.forename: B
authors.initials: B
authors.lastname: Svensson
mesh_terms: D000118:Acetylglucosaminidase / Q000378:metabolism; D001120:Arginine; D001234:Aspergillus niger / Q000201:enzymology*; D055598:Chemical Phenomena; D002621:Chemistry; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism*; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008239:Lysine; D008320:Maltose / Q000378:metabolism; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D013213:Starch / Q000378:metabolism; D013329:Structure-Activity Relationship; D014443:Tyrosine
chemical_list: D014443:Tyrosine; D006639:Histidine; D008320:Maltose; D013213:Starch; D001120:Arginine; D005087:Glucan 1,4-alpha-Glucosidase; D000118:Acetylglucosaminidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008239:Lysine