Metal Activated Enzymes versus Metalloenzymes

Enzymes that depend on metal ions as cofactors fall into two categories: metal-activated enzymes and metalloenzymes. As the name implies, metal-activated enzymes are prompted to greater catalytic activity by the presence of a mono- or divalent metal ion exterior to the protein (in the assay medium). The metal may activate the substrate (e.g., Mg2+ with ATP), engage the enzyme directly, or enter into equilibrium with the enzyme exploiting its ionic charge to render a more favorable substrate binding or catalytic environment. Therefore, metal-activated enzymes require the metal to be present in excess, perhaps 2-10 times more than the enzyme concentration. Because the metal cannot be bound in a more permanent way, metal-activated enzymes typically lose activity during purification. An example is pyruvate kinase, which has a specific requirement for K+ and is inactivated by dialysis (diffusion through a semiporous membrane). Other examples of metal-activated enzymes are shown in Table 2.

Metalloenzymes, in contrast, have a metal cofac-tor bound firmly to a specific region on the protein surface. Some may even require more than one metal ion and in rare instances could be two different metals as, for example, in Cu2,Zn2 superoxide dismutase. With few exceptions, trace metals fit into the picture as cofactors for metalloenzymes. Fe, Zn, Cu, and Mn, referred to as first transition series metals, are the most common. Their counterparts,

Table 2 Metal-activated enzymes and metalloenzymes

Metal or metal cofactor

Enzyme

Function

Metal-activated enzymes

K+

Pyruvate kinase

Synthesize pyruvate

Mg2+

Hexokinase

Phosphorylate

glucose

DNase

Cleave DNA

RNase

Cleave RNA

ATPase

Cleave ATP

Metalloenzymes

Cu2+, Zn2+

Superoxide

Destroy superoxide

dismutase

anion

Fe

Catalase

Destroy H2O2

Zn

Alcohol

Metabolize alcohol

dehydrogenase

DNA polymerase

Synthesize DNA

Mn

Pyruvate

Synthesize

carboxylase

oxaloacetate

Arginase

Synthesize urea

Ca

Alpha amylase

Cleave glycogen,

starch

Square planar dsp2

Square planar dsp2

Octahedral d2sp3

Tetrahedral dsp3

Figure 1 Some common geometries of metal complexes.

Mg, K, Ca, and Na, are not considered 'trace' and only in rare instances are these so-called macroelements strongly bound to the surface of enzymes. Tight binding precludes loss of the metal ion by dialysis or loss to weakly dissociating agents. Metalloenzymes, however, can lose their metal cofactor and hence be rendered inactive when treated with metal chelators that have a stronger binding affinity than the enzyme and out compete the enzyme protein for the metal ion. As prosthetic groups, metals in metalloenzymes have a stoichio-metric relationship (metal ion-enzyme protein ratio) represented by a whole integer. Metalloenzymes seldom are primed to greater activity by adding its conjugate metal ion to the enzyme. Spatial geometry is also a concern. Metals in the first transition series metals (Mn, Fe, Co, Ni, Cu, Zn) must adhere to strict geometric configurations around the metal-binding site. Examples of the more common geometrical arrangements are shown in Figure 1. For metals in the first transition series one takes note of the 3d and 4s orbitals in assigning valence states and likely geometric shapes. Apart from those with Zn, enzymes with first transition series metals tend to be highly colorful; for example, the beautiful red color of hemoglobin (iron) or the blue color of ceruloplasmin (whose name means heavenly blue) associated with copper. Table 3 gives some examples of metalloenzymes and the specific metal each requires.

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Responses

  • lily ross
    What is the difference between metalloenzymes and metalactivated enzymes?
    3 years ago
  • luka
    What are metalloenzymes and metal activated enzymes ?
    3 years ago
  • GINO
    What are the enzyme acrivated by trace metals?
    3 years ago
  • Mario
    What are metal activated enzyme explain with example?
    3 years ago
  • conlan kennedy
    What are metal active enzyme &exaplain with example?
    3 years ago
  • Joseph
    What are mettalo enzymes?
    3 years ago
  • arsenio
    What are metal activated enzyme briefly explain with example?
    3 years ago
  • alina
    What is meaning metal activated of enzyme?
    3 years ago
  • vihtori
    Is alcohol dehydrogenase a metalloenzyme or a metal activated enzyme?
    3 years ago
  • Marlene Lewis
    Is hexokinase a metalloenzyme?
    3 years ago
  • grimalda
    What is metallo enzyme?
    3 years ago
  • autumn
    How will you distinguish metalloenzymes from metal activated enzymes?
    3 years ago
  • Isengrim
    What are metal proteins and examples?
    3 years ago
  • Sara Häggman
    How mg2 activate enzyme activity?
    2 years ago
  • lorenzo
    What are metal activated proteins?
    2 years ago
  • agatino
    Is metals are enzymes?
    2 years ago
  • mhairi
    What is metal activated protein?
    2 years ago
  • Ciriaca
    What are the differences between metalloenzyme and metal activated enzyme?
    2 years ago
  • luam
    What is metallic ion activating enzymes?
    2 years ago
  • tesfay
    What is metalloenzyme notes?
    2 years ago
  • TESS
    Is metal related enzymes or cofactors are same?
    2 years ago
  • Laura
    Is metal activating enzyme the same as metalo enzyme?
    2 years ago
  • robert
    What are metallic activatorsgive three types?
    2 years ago
  • bungo
    What happen if we removed the metal from metalloenzyme?
    2 years ago
  • zemzem
    Which constituent of the metallo enzyme is referred to as enzyme activator?
    1 year ago
  • essi wahlman
    What is metalloenzyem?
    1 year ago
  • Amanuel
    What happens if we remove the matel in metallo enzyme?
    1 year ago
  • jennifer warrick
    What are metal detectors activated enzymes?
    1 year ago
  • vickie
    What are metal activating enzyme and explain there catalyst scheme?
    1 year ago
  • antoinette
    Which constituent of the metalloenzyme is usually referred to as the enzyme activator?
    1 year ago
  • Assunta
    Which constituent metallo enzymes is referred to ad activator?
    1 year ago
  • cotman
    Which constituent of the metalloenzymes is usually referred to as the enzymes activator?
    1 year ago
  • Sophia
    Which constituent of the metallo enzyme is usually refered to as the enzyme activator/?
    1 year ago
  • LAURA BROCKHOUSE
    What distinguishes metallo enzyme from metal activated enzyme?
    11 months ago
  • anneli
    Is there a relationship between metal ions in natural enzymes with?
    4 months ago
  • semrawit
    What is metalloenzyme and metal activated enzymes?
    3 months ago
  • roger lowe
    How many enzymes require metal?
    2 months ago
  • robinia
    What Is Metal Activated Protein An Complexes?
    2 months ago

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