Identification of a 23 kDa protein from maize photoaffinity-labelled with 5-azido-[7-3H]indol-3-ylacetic acid.
A 23 kDa protein (p23) was identified in microsomal extracts from maize coleoptiles by photoaffinity labelling with 5-azido-[7-3H]indol-3-ylacetic acid ([3H]N3IAA). Labelling of p23 was blocked by unlabelled IAA, N3IAA, indol-3-ylbutyric acid and indol-3-yl-lactate. In addition, labelling was efficiently decreased by tryptophan, as well as by the scavenger p-aminobenzoic acid. Labelling was, however, not affected by synthetic auxins such as 1-naphthylacetic acid or 2,4-dichlorophenoxyacetic acid. Competition data suggest that the label was probably bound via the indole ring, and hence labelling was not specific for auxins. The 23 kDa protein was solubilized from crude microsomes by extraction with Triton X-100 and purified to homogeneity by ion-exchange, size-exclusion and reversed-phase chromatography. After electroblotting, the amino acid sequences of the p23 N-terminus as well as the several tryptic peptides were obtained. Database comparisons revealed sequence identity with a maize manganese superoxide dismutase. We conclude that photoaffinity labelling of p23 was pseudo-affinity, and therefore the binding site for IAA is not specific.
Max-Planck-Institut für Züchtungsforschung, Köln, Germany.
J
J
Feldwisch
R
R
Zettl
N
N
Campos
K
K
Palme
D010129:4-Aminobenzoic Acid / Q000494:pharmacology; D000345:Affinity Labels; D000595:Amino Acid Sequence; D001386:Azides / Q000378:metabolism*; D001667:Binding, Competitive; D002851:Chromatography, High Pressure Liquid; D007210:Indoleacetic Acids / Q000378:metabolism*; D008345:Manganese; D008861:Microsomes / Q000737:chemistry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010777:Photochemistry; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D013696:Temperature; D014316:Tritium; D014364:Tryptophan / Q000494:pharmacology; D003313:Zea mays / Q000737:chemistry*
D000345:Affinity Labels; D001386:Azides; D007210:Indoleacetic Acids; D014316:Tritium; D008345:Manganese; C068520:5-azido-1H-indole-3-acetic acid; D014364:Tryptophan; D013482:Superoxide Dismutase; D010129:4-Aminobenzoic Acid