May 20, 1986

A probe of the active site acidity of carboxypeptidase A

Biochemistry
W L Mock, J T Tsay

Abstract

The substrate analogue 2-(1-carboxy-2-phenylethyl)-4-phenylazophenol is a potent competitive inhibitor of carboxypeptidase A. Upon ligation to the active site, the azophenol moiety undergoes a shift of pKa from a value of 8.76 to a value of 4.9; this provides an index of the Lewis acidity of the active site zinc ion. Examination of the pH dependence of Ki for the inhibitor shows maximum effectiveness in neutral solution (limiting Ki = 7.6 X 10(-7) M), with an increase in Ki in acid (pK1 = 6.16) and in alkaline solution (pK2 = 9.71, pK3 = 8.76). It is concluded that a proton-accepting enzymic functional group with the lower pKa (6.2) controls inhibitor binding, that ionization of this group is also manifested in the hydrolysis of peptide substrates (kcat/Km), and that the identity of this group is the water molecule that binds to the active site metal ion in the uncomplexed enzyme (H2OZn2+L3). Reverse protonation state inhibition is demonstrated, and conventional concepts regarding the mechanism of peptide hydrolysis by the enzyme are brought into question.

  • References19
  • Citations4

Mentioned in this Paper

In Vivo NMR Spectroscopy
Carboxypeptidase A5
Carboxypeptidase
Hydrogen-Ion Concentration
Azo Compounds
2-(1-carboxy-2-phenylethyl)-4-phenylazophenol, (L)-isomer

About this Paper

Trending Feeds

COVID-19

Coronaviruses encompass a large family of viruses that cause the common cold as well as more serious diseases, such as the ongoing outbreak of coronavirus disease 2019 (COVID-19; formally known as 2019-nCoV). Coronaviruses can spread from animals to humans; symptoms include fever, cough, shortness of breath, and breathing difficulties; in more severe cases, infection can lead to death. This feed covers recent research on COVID-19.

Bone Marrow Neoplasms

Bone Marrow Neoplasms are cancers that occur in the bone marrow. Discover the latest research on Bone Marrow Neoplasms here.

IGA Glomerulonephritis

IgA glomerulonephritis is a chronic form of glomerulonephritis characterized by deposits of predominantly Iimmunoglobin A in the mesangial area. Discover the latest research on IgA glomerulonephritis here.

Cryogenic Electron Microscopy

Cryogenic electron microscopy (Cryo-EM) allows the determination of biological macromolecules and their assemblies at a near-atomic resolution. Here is the latest research.

STING Receptor Agonists

Stimulator of IFN genes (STING) are a group of transmembrane proteins that are involved in the induction of type I interferon that is important in the innate immune response. The stimulation of STING has been an active area of research in the treatment of cancer and infectious diseases. Here is the latest research on STING receptor agonists.

LRRK2 & Immunity During Infection

Mutations in the LRRK2 gene are a risk-factor for developing Parkinson’s disease. However, LRRK2 has been shown to function as a central regulator of vesicular trafficking, infection, immunity, and inflammation. Here is the latest research on the role of this kinase on immunity during infection.

Antiphospholipid Syndrome

Antiphospholipid syndrome or antiphospholipid antibody syndrome (APS or APLS), is an autoimmune, hypercoagulable state caused by the presence of antibodies directed against phospholipids.

Meningococcal Myelitis

Meningococcal myelitis is characterized by inflammation and myelin damage to the meninges and spinal cord. Discover the latest research on meningococcal myelitis here.

Alzheimer's Disease: MS4A

Variants within membrane-spanning 4-domains subfamily A (MS4A) gene cluster have recently been implicated in Alzheimer's disease by recent genome-wide association studies. Here is the latest research.