l-Amino acid oxidases (LAAOs) are flavoproteins, which use oxygen to deaminate l-amino acids and produce the corresponding -keto acids, ammonia, and hydrogen peroxide. Here we describe the heterologous expression of LAAO4 from the fungus Hebeloma cylindrosporum without signal sequence as fusion protein with a 6His tag in Escherichia coli and its purification. 6His-hcLAAO4 could be activated by exposure to acidic pH, the detergent sodium dodecyl sulfate, or freezing. The enzyme converted 14 proteinogenic l-amino acids with l-glutamine, l-leucine, l-methionine, l-phenylalanine, l-tyrosine, and l-lysine being the best substrates. Methyl esters of these l-amino acids were also accepted. Even ethyl esters were converted but with lower activity. K-m values were below 1mM and v(max) values between 19 and 39Umg(-1) for the best substrates with the acid-activated enzyme. The information for an N-terminal aldehyde tag was added to the coding sequence. Co-expressed formylglycine-generating enzyme was used to convert a cysteine residue in the aldehyde tag to a C-formylglycine residue. The aldehyde tag did not change the properties of the enzyme. Purified Ald-6His-hcLAAO4 was covalently bound to a hexylamine resin via the C-formylglycine residue. The immobilized enzyme could be reused repeatedly to generate phenylpyruvate from l-phenylalanine with a total turnover number of 17,600 and was stable for over 40days at 25 degrees C.