Maleylation of Alkaline Mesentericopeptidase

Seven of the eight e‐amino groups of the lysyl residues in alkaline mesentericopeptidase were modified when the enzyme was treated with maleic anhydride. Some conclusions about the degree of exposure to the solvent of these amino acid side chains were made. The results are discussed in relation to the X‐ray crystallographic model of subtilisin type BPN. The maleylation of alkaline mesentericopeptidase caused a loss of its elastolytic activity while the rate of cleavage of casein was slightly increased. Maleyl‐enzyme has the same activity as the native mesentericopeptidase with the synthetic ester substrates Nα‐tosyl‐L‐arginine methyl ester and N‐acetyl‐L‐tyrosine ethyl ester. It was concluded that the additional negatively charged groups were introduced outside the primary binding sites for small substrates. The effects of varying the salt concentration on mesentericopeptidase activities were studied and conclusions about the forces responsible for the formation of the enzyme‐substrate complexes were drawn.