Sansei karubokishi pepuchida-ze (Ei shi-pi-)

Acid carboxypeptidase (ACP)

Because serine is this enzyme’s active site, it is also known as serine carboxypeptidase. It works on the peptide bond at the end of proteins and peptides, successively cutting off amino acids.

If large quantities of acid carboxypeptidase from the koji exist in the moromi, the level of amino acids in the sake increases. Amino acids are important contributors of umami and other flavours, but too high a level can lead to zatsu-mi off-flavours. Furthermore, amino acids contribute to sake colouring ( chaku-shoku ) and accelerate ageing, so research is being carried out into ways to make koji and enzyme preparations which have low levels of this enzyme.

The enzyme also exists in an inactive state in yeast vacuoles. In the late stages of fermentation, it becomes activated when yeast dies or autolyzes, contributing to an increase in amino acid levels.

Measuring acid carboxypeptidase is done by reacting the enzyme solution with carbobenzoxy-glutamyl-tyrosine (a synthetic substrate) for a fixed length of time, then the tyrosine liberated is measured by ninhydrin test.