Problem	Possible Cause	Solution
Poor conversion to oxime product	Low yield of transamination reaction	Increase the concentration of PLP, screening from 10 mM to 100 mM Increase the incubation time or the temperature of the transamination reaction
	Low yield of oxime formation reaction	Increase the equivalents of alkoxyamine Lower the pH during oxime formation step Use aniline catalysis, as reported by Dirksen et al., 2006 Check quality of alkoxyamine reagent by NMR
High conversion to undesired PLP adduct	Byproduct formation	Use lower concentrations of PLP Use shorter reaction times To identify common byproducts, see the table of common mass adducts
Nominal reactivity	Inaccessible or unreactive N-terminal residues	Consider mutagenesis
Protein precipitation	PLP solution is too acidic	Check and adjust pH of PLP solution before mixing with protein
	Protein insolubility	The transamination reaction can be run under buffer, pH, and temperature conditions that vary from those listed in the Basic Protocol. Alter these parameters as dictated by the stability of the target protein