Excess zinc ions are a competitive inhibitor for carboxypeptidase A

Journal Article · Tue Oct 06 04:00:00 EDT 1987 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00394a041· OSTI ID:5402043

Hirose, J; Ando, S; Kidani, Y

The mechanism for inhibition of enzyme activity by excess zinc ions has been studied by kinetic and equilibrium dialysis methods at pH 8.2, I = 0.5 M. With carboxypeptidase A (bovine pancreas), peptide (carbobenzoxyglycyl-L-phenylalanine and hippuryl-L-phenylalanine) and ester (hippuryl-L-phenyl lactate) substrates were inhibited competitively by excess zinc ions. The K/sub i/ values for excess zinc ions with carboxypeptidase A at pH 8.2 are all similar. The apparent constant for dissociation of excess zinc ions from carboxypeptidase A was also obtained by equilibrium dialysis at pH 8.2 and was 2.4 x 10/sup -5/ M, very close to the K/sub i/ values above. With arsanilazotyrosine-248 carboxypeptidase A ((Azo-CPD)Zn)), hippuryl-L-phenylalanine, carbobenzoxyglycyl-L-phenylalanine, and hippuryl-L-phenyl lactate were also inhibited with a competitive pattern by excess zinc ions, and the K/sub i/ values were (3.0-3.5) x 10/sup -5/ M. The apparent constant for dissociation of excess zinc ions from arsanilazotyrosine-248 carboxypeptidase A, which was obtained from absorption changes at 510 nm, was 3.2 x 10/sup -5/ M and is similar to the K/sub i/ values for ((Azo-CPD)Zn). The apparent dissociation and inhibition constants, which were obtained by inhibition of enzyme activity and spectrophotometric and equilibrium dialysis methods with native carboxypeptidase A and arsanilazotyrosine-248 carboxypeptidase A, were almost the same. This agreement between the apparent dissociation and inhibition constants indicates that the zinc binding to the enzymes directly relates to the inhibition of enzyme activity by excess zinc ions. Excess zinc ions were competitive inhibitors for both peptide and ester substrates. This behavior is believed to arise by the excess zinc ions fixing the enzyme in a conformation to which the substrates cannot bind.

• Research Organization: Nagoya City Univ., Japan
• OSTI ID: 5402043
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:20; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550200 -- Biochemistry
550300* -- Cytology
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
BODY
CARBOXYPEPTIDASES
CATIONS
CATTLE
CHARGED PARTICLES
DIGESTIVE SYSTEM
DOMESTIC ANIMALS
DOSE-RESPONSE RELATIONSHIPS
ENDOCRINE GLANDS
ENZYME ACTIVITY
ENZYME INHIBITORS
ENZYMES
GLANDS
HYDROLASES
IONS
KINETICS
MAMMALS
ORGANS
PANCREAS
PEPTIDE HYDROLASES
REACTION KINETICS
RUMINANTS
VERTEBRATES
ZINC COMPOUNDS