title: Essential arginine residues in maize starch synthase IIa are involved in both ADP-glucose and primer binding.
abstract: The arginine-specific reagent phenylglyoxal inactivated the activity of maize starch synthase IIa (SSIIa), due to the modification of at least one arginine residue out of a possible 42. The addition of ADPGlc completely protected SSIIa from the inactivation, indicating that arginine may be involved in the interaction of this anionic substrate with SSIIa. However, site-directed mutagenesis of the conserved Arg-214 in SSIIa showed that this amino acid is important for apparent affinity of SSIIa for its primer (amylopectin and glycogen), as evidenced by a marked increase in the K(m) for primer upon substitution of this amino acid with no concomitant change in V(max), K(m) for ADPGlc, or secondary structure. Therefore, Arg-214 of SSIIa appears to play a role in its primer binding.
authors.affiliation: ExSeed Genetics, L.L.C., 1568 Food Science Building, Iowa State University, Ames, IA 50011-1061, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Imparl-Radosevich
authors.forename: P L
authors.initials: PL
authors.lastname: Keeling
authors.forename: H
authors.initials: H
authors.lastname: Guan
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000687:Amylopectin / Q000378:metabolism*; D001120:Arginine; D001665:Binding Sites; D020134:Catalytic Domain; D002942:Circular Dichroism; D017124:Conserved Sequence; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D005964:Glucosyltransferases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006639:Histidine / Q000235:genetics; D007527:Isoenzymes; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010658:Phenylglyoxal / Q000494:pharmacology; D010940:Plant Proteins; D011994:Recombinant Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D013214:Starch Synthase; D003313:Zea mays / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010940:Plant Proteins; D011994:Recombinant Proteins; D006639:Histidine; D000244:Adenosine Diphosphate; D006003:Glycogen; D000687:Amylopectin; D001120:Arginine; D005964:Glucosyltransferases; C111377:starch synthase II; D013214:Starch Synthase; D005947:Glucose; D010658:Phenylglyoxal