The liberated glucose was detected with a Tris-glucose oxidase-peroxidase reagent at A405 in a Tecan Sunrise™ microplate reader (Tecan Austria GmbH, Grödig, Austria) adjusted to the method of Dahlqvist (1968). The activity of aminopeptidase-N (APN, EC 3.4.11.2) in BBM was determined according to Willing and Van Kessel