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Related Concept Videos

Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
Cofactors and Coenzymes01:24

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic interactions or acid-base reactions. However, amino acids cannot catalyze oxidation-reduction and group transfer reactions and need to be aided by non-protein components called cofactors. Cofactors are also referred to as the chemical teeth of an enzyme.
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper...
Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
ATP Synthase: Mechanism01:48

ATP Synthase: Mechanism

In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased ATP...
Sulfur Assimilation01:20

Sulfur Assimilation

Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to become...
Electron Transport Chain: Complex III and IV01:43

Electron Transport Chain: Complex III and IV

During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...

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Optimized Protocol for the Extraction of Proteins from the Human Mitral Valve
09:13

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Published on: June 14, 2017

Saposin B is a human coenzyme q10-binding/transfer protein.

Guangzhi Jin1, Hiroshi Kubo, Misato Kashiba

  • 1School of Bionics, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.

Journal of Clinical Biochemistry and Nutrition
|April 4, 2008
PubMed
Summary

Saposin B, a protein found in human urine, binds and transports Coenzyme Q10 (CoQ10). This discovery reveals a novel mechanism for CoQ10 transport in cells, impacting cellular energy production and antioxidant defense.

Keywords:
HepG2coenzyme Q10 binding proteinsaposin Bspermurine

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Medicine

Background:

  • Coenzyme Q10 (CoQ10) is vital for mitochondrial ATP production and acts as a cellular antioxidant.
  • The hydrophobic nature of CoQ10 suggests a need for a binding and transport protein, though none were previously identified.

Purpose of the Study:

  • To identify and characterize a CoQ10-binding protein in human samples.
  • To investigate the role of saposin B in CoQ10 binding and transport.

Main Methods:

  • Purification of a CoQ10-binding protein from human urine.
  • Identification of the protein as saposin B using monoclonal antibodies.
  • Quantification of CoQ10-saposin B molar ratios in various human samples (urine, HepG2 cells, sperm).
  • Assays to determine lipid binding affinity and pH-dependent binding/donation activities.

Main Results:

  • Saposin B was purified from human urine and identified as a CoQ10-binding protein.
  • Cellular saposin B was confirmed to bind CoQ10 in human sperm and HepG2 cells.
  • Saposin B demonstrated preferential binding to CoQ10 over other lipids and showed pH-dependent binding and donation activities.
  • The molar ratios of CoQ10 to saposin B varied across different biological samples.

Conclusions:

  • Saposin B functions as a CoQ10-binding and transport protein in human cells.
  • This finding provides new insights into CoQ10 homeostasis and cellular function.
  • Saposin B may play a significant role in delivering CoQ10 to cellular membranes and mitochondria.