Yoshikazu Matsumura

Bitter Peptides in Cow Milk Casein Digests with Bacterial Proteinase: Part I. Isolation and Determination of Amino Acid Sequence of a Bitter Peptide

Isolation and determination of amino acid sequence of the bitter peptides formed in the digestion of cow milk casein with alkaline proteinase of Bacillus subtilis were investigated. The casein digest with the enzyme was extracted with butanol and the extracted bitter peptides were fractionally purified by treating with several other organic solvents followed by subjecting to chromatography and gel-filtration. The amino acid sequence of one of the bitter peptides was determined as follows: Arg-Gly-Pro-Pro-Phe-Ileu-Val. Liberation of N-terminal Arg with trypsin or bacterial aminopeptidase did not affect the bitterness. Also, splitting off of Val and Ileu or Ileu-Val at the C-terminus by carboxypeptidase, or a bacterial neutral proteinase gave no influence on the bitterness. However, liberation of Arg and Gly from the peptide with bacterial aminopeptidase gave rise to a non bitter peptide.

Intracellular Peptidase of Bacillus subtilis :Part III. Effects of Metal Ions on Activity and Specificity of Aminopeptidase of Bacillus subtilis

An electrophoretically pure preparation of aminopeptidase was isolated from the cells of a strain of Bacillus subtilis which secreted saccharifying α-amylase. The purified peptidase was active only in the presence of manganese and cobaltous ions. Both the metallic ions were effective to a similar degree for the enzyme on most of the peptides used as the substrate. However, for hydrolysis of leucine amide by the enzyme was effective only cobaltous ion and, in this case, manganese ion showed to act as a competitive inhibitor. On the other hand, for hydrolysis of certain other peptides such as glycyl proline, quite the opposite relationship was observed between those metallic ions. In the present paper is also described a new micro-assay method of amidase activity shown by the peptidase.