Beta-aminopeptidase that can cleave synthetic beta-peptides which consist of backbone-elongated beta-amino acid residues that are not processed by common proteolytic enzymes. Can cleave the beta-peptides beta-homoVal-beta-homoAla-beta-homoLeu and beta-homoAla-beta-homoLeu. Requires a beta-amino acid at the N-terminus of peptide substrates and cleaves the peptide bond between the N-terminal beta-amino acid and the amino acid at the second position of tripeptidic substrates of the general structure H-betahXaa-Ile-betahTyr-OH according to the following preferences with regard to the side chain of the N-terminal beta-amino acid: aliphatic and aromatic > OH-containing > hydrogen, basic and polar. beta-homoVal-beta-homoAla-beta-homoLeu and beta-homoAla-beta-homoLeu. Cleaves N-terminal beta-homoamino acids from peptides composed of 2 to 6 amino acids. Inhibited by AEBSF (4-(2-aminoethyl)benzenesulfonyl fluoride, Pefabloc SC). Optimum pH is 10. Heterooctamer of 4 heterodimers ((alpha:beta)4); each heterodimer is composed of an alpha subunit and a beta subunit processed from the same precursor. Autoproteolytic processing to generate the alpha and beta subunit is required for self-activation and is proposed to use a similar mechanism as substrate cleavage. S.microcystinivorans can degrade microcystin, a cyclic, toxic heptapeptide that contains beta-peptidic substructures. Belongs to the peptidase S58 family.