Oxidative stress (general considerations)

Today I decided to make a post on a very important topic, oxidative stress. This subject is often referred to in biochemistry classes (and not only!), but it is not always clear to the speaker or to the audience, what it actually represents.
Nevertheless, the idea is simple to understand ... As I say many times in my classes, we have a bad habit, which kills us slowly, without exception: we spend our lives breathing oxygen! And this molecule, so important for our biochemistry, in particular for aerobic metabolism, is what kills us slowly, and makes us grow old. And do not hesitate, if we do not die of an accident, or of some illness, we will die because we have been breathing O2 during our life! :)
So, what does oxygen contain that makes it so dangerous? Basically nothing, that is, the molecule itself is harmless to our molecules/cells. The problem is in its susceptibility to suffer partial reductions, that is, to capture electrons. In fact, we are continually forming the so-called reactive oxygen species, which are essentially 3: the hydroxyl radical (free radical), the superoxide anion (free radical) and hydrogen peroxide. Of these 3, the first two are more aggressive because they are free radicals. Free radicals are molecules that have an unpaired electron (which is why they are represented with a black speckle, which is that unpaired electron).  

The electrons have a serious problem, they do not like to walk alone, so they will look for "companionship" in the first molecule that appears ahead, be it a lipid, a protein or a nucleic acid. That is, reactive oxygen species are highly reactive molecules, they are powerful oxidizing agents, which will react with our biomolecules, removing an electron and altering/destroying them. And the problem is that although the free radical ceases to be when it picks up an electron, the molecule with which it reacts becomes a free radical, giving rise to a destructive chain process.
To counteract this, our cells have several defenses, called antioxidants. Therefore, oxidative stress arises when we have an imbalance between the pro-oxidants (reactive oxygen species and reactions that produce them) and the antioxidants (processes that prevent the formation and/or action of the pro-oxidants), favoring the first, or disfavoring the seconds.

Cartoon about lipids and carbohydrates

Glycogenin

The glycogenin is a protein whose main function is to be the initiator molecule of glycogen synthesis (glycogenesis), a process that allows the storage of glucose residues in the form of a polysaccharide. Glucose residues are added to glycogenin through α-1,4 bonds. The first step in the glycogen synthesis is indeed the synthesis of this protein. Each glycogen molecule is linked to a glycogenin by a glycosidic linkage which involves the first glucose residue of the chain and a tyrosine residue of glycogenin. The glycogenin designation stems from the fact that this protein is involved in the genesis of glycogen, by functioning as a primer in the formation of a new glycogen molecule.The glycogenin through its glucosyltransferase activity, binds covalently to itself a glucose molecule (from UDP-glucose - the active form of glucose). Then, the glycogenin forms a compact complex with glycogen synthase, the enzyme responsible for glycogen synthesis. After the addition of up to 7 more glucose residues (from UDP-glucose) mediated again by the activity of glucosyltransferase of glycogenin. Finally, glycogen synthase and branching enzyme enter in action, being glycogenin covalently linked to the unique reducing end of the glycogen molecule.
In humans there are two isoforms of glycogenin which can be expressed as glycogenin-1, having a molecular weight of 37 kD, and encoded by the GYG gene that is expressed mainly in muscle, or as glycogenin-2 having a molecular weight of 66 kDae encoded by GYG2 gene which is expressed mainly in the liver, cardiac muscle and other types of tissues except skeletal muscle

Disability glycogenin-1 (GYG1) - Mutation of the gene GYG1
A glycogenin-1 deficiency was detected in its gene, GYG1, which revealed a nonsense mutation in one allele and a missense mutation in another allele. A missense mutation results from inactivation of the autoglycosilation of glycogenin-1, which is required for the initiation of glycogen synthesis in muscle. The glycogenin-1 autoglycosilation occurs at Tyr195 by the action of glucose-1-O-tyrosine. A missense mutation of this residue results in inactivation of the autoglycosilation. However, it was also demonstrated that missense mutations affecting other residues of glycogenin 1-cause problems on autoglycosilation.
Phenotypic characteristics of skeletal muscle in a patient with this disorder are muscle glycogen depletion, mitochondrial proliferation and marked predominance of slow twitch amd oxidized muscle fibers. Mutations in glycogenin-1 gene GYG1 are also causes of cardiomyopathy and arrhythmia.

Text written by:

Daniela Marinheiro

Carla Marty

Maria Rocha

Marta Rodrigues

Rita Osório

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Video about reducing sugars

Metabolic map about NO signalling pathway

Enolase

Enolase is an enzyme, more particularly, an active metalloenzyme. This enzyme belongs to the family of lyases, the hydro-lyases, breaking the carbon-oxygen bonds, and is present in all tissues and organisms involved in glycolysis or fermentation. The optimal pH of this enzyme is 6.5 in humans.Its main function is to intervene in the 9th step of glycolysis (the penultimate step in this metabolic pathway), a step in which occurs the dehydration of 2-phosphoglycerate (2-PG) in phosphoenolpyruvate (PEP), a product that will be used in the next and final step for the production of energy (ATP).
Enolase has three different isoforms: the ENO1 or alpha-enolase (in muscle tissue); ENO2 or gamma-enolase or neuro specific enolase (in neurons); ENO3 or beta-enolase (in skeletal muscle cells). Enolase has a molecular weight of about 100000 Daltons (depending on the isoform). In humans, the α-enolase has two antiparallel subunits, which have two domains that establish hydrophobic interactions. The subunits interact via salt bridges, involving arginine and glutamate.
The specific enolase to neurons is released in a wide variety of diseases, such as multiple sclerosis or stroke, or myocardial infarction.
In several medical experiments, it was employed enolase concentrations in samples in an attempt to diagnose certain conditions and its severity. Several studies demonstrated that different levels of enolase may also be associated with tumor growth or with the occurrence of myocardial infarction or stroke, so it was inferred that the levels of enolase serve as an indicative of the prognostic evaluation of victims of cardiac arrest.
Enolase inhibitors have been utilized in health care for the treatment and prevention various diseases, such as anti-trypanosome drugs and more recently as anticancer agents. Enolase can be inhibited by fluoride ion (F-). The fluoride forms a complex with magnesium and phosphate, which binds to the active center of the enzyme rather than the substrate 2-PG, preventing the conversion of 2-PG into PEP, decreasing the production of PEP and, consequently, ATP.
Intake of fluoride-containing water inhibits the catalytic activity of enolase of bacteria present in oral cavity (highly dependent on glycolysis due to the anaerobic environment), interrupting glycolysis and, thus, bacterial fermentation (decreased acid production), preventing the formation of dental caries.

Text written by:
Inês Carvalho
Junjie Lin
Maria Alves
Susana Pinto
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Cartoon - carbohydrates

Video about carbohydrates biochemistry