Malate Dehydrogenase

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Malate Dehydrogenase

Enzymes and hormones are common types of proteins and are formed from long chains of amino acids. Protein is primal for the growth and maintenance of body tissues. However, these proteins are continuously in a position of turnover. Usually, the human body breaks down similar protein amounts it uses in creating and repairing tissues. Under abnormal circumstances, the human body can break down more protein than it is making, leading to increased body needs. Such occurrences are common during illness, pregnancy, and while breastfeeding. Individuals from injuries or surgeries, active people, and adults require higher contents of protein. Proteins play a significant role in a biochemical reaction. Enzymes primarily help biochemical reactions inside and outside the body cells (Isralewitz, Gao & Schulten, 2001). Enzymes are structurally adapted to combining with other molecules within substrates, catalyzing vitally important body metabolism reactions. Digestive enzymes such as lactase and sucrase function outside the cell and aid in digesting sugar. Some molecules also need vitamins or minerals to facilitate chemical reactions (Isralewitz, Gao & Schulten, 2001). Digestion, energy production, muscle contraction, and blood clotting are the most common bodily functions that rely on enzymes.

Proteins act as chemical messengers that facilitate communication between body cells, tissues, and organs. Endocrine tissues create hormones, then taken to the blood’s target tissues, where they stick to protein receptors (Isralewitz, Gao & Schulten, 2001). Hormones can be categorized as steroids, amines, and protein and peptides. Protein and peptides are created from a few to several hundred amino acids. The sex hormones estrogen, and testosterone, are the commonly known steroids made from fat cholesterol. Amines are made from tryptophan or tyrosine amino acids, which help create hormones associated with sleep and metabolism. Proteins and polypeptides compose of most body hormones (Isralewitz, Gao & Schulten, 2001). Proteins like keratin, collagen, and elastic are fibrous and give the cells and tissues stiffness and rigidity. Keratin is present in human skin, hair, and nails. The most abundant protein in the human body is arguably collagen and helps form bones, tendons, ligaments, and skin. Elastin helps the body to return to its original shape after stretching or contracting. It is massively flexible than collagen usually helps body organs such as the uterus, lungs, and arteries.

Protein plays a significant in controlling acids, bodily fluids, and bases concentrations in the body. In other words, it regulates the body’s pH. pH scale measures the balance between the acids and bases, and they range from 0 to 14. 0 present the most acidic, 7 is neutral, and 14 is most alkaline. For example, the stomach acid, tomato juice, black coffee, human blood, milk of magnesia, and soapy water have pH 2, 4, 5, 7.4, 10, and 12, respectively (Isralewitz, Gao & Schulten, 2001). Maintaining constant pH ranges is vital since a slight change in it has the potential to cause harm. Proteins help the body to regulate pH. Hemoglobin helps to regulate the pH value of the blood. Also, proteins balance body fluids by regulating body metabolisms—the albumin and globulin help control the body’s fluid balance by attracting and retaining water (Isralewitz, Gao & Schulten, 2001). Failure to consume adequate proteins results in low albumin levels and globulin in the body, thus making it impossible for the body to maintain blood in the blood vessels, eventually forcing the body fluid into spaces between the cells.

Malate Dehydrogenase (MDH)

Malate dehydrogenase (MDH) plays a significant role in the metabolic pathway of the Krebs cycle (tricarboxylic acid cycle), essential to cells cellular respiration. MDH is also involved in glyoxylate bypass, oxidation balance, gluconeogenesis, and synthesis of amino acids. It has numerous isozymes and is categorized as an oxidoreductase (Takahashi-Íñiguez et al. 2016). Malate dehydrogenase is often present in mitochondria and cytoplasm. MDH catalyzes malate reaction to oxaloacetate in mitochondria, while in cytoplasm, it does the reverse to allow transport, that is, catalyzing oxaloacetate to malate (Takahashi-Íñiguez et al. 2016). MDH enzyme comprises of either a dimer or tetramer-based enzyme location and its host. It is vastly distributed among living things, that is, prokaryotic and eukaryotic organisms. MDH has crystal structures based on varied bacterial sources that help identify regions involved in substrate and cofactor binding, not to mention significant residues for the dimer-dimer interface.

Malate dehydrogenase has a heterogeneous molecular weight, subunit structure, and catalytic properties. Cytosolic MDH and mitochondrial MDH are major malate dehydrogenase isozymes in most eukaryotic cells. MDH isozymes in plants, and some eukaryotic microorganisms are present in organelles like glyoxysomes, chloroplasts, and peroxisomes (Takahashi-Íñiguez et al. 2016). There exist little literature report concerning molecular characteristics of bacterial malate dehydrogenase. MDH present in prokaryotes is homodimeric and tetrameric. The homodimeric enzyme is present in Gram-negative microorganism, while Gram-positive bacteria and archaea have a tetrameric malate dehydrogenase.

Concerning MDH primary and secondary structure, it belongs to the NAD-dependent dehydrogenases. They comprise of large protein molecules such as dimers and homotetramers. Their polypeptide chain varies in lengths at about 350 residues. The sequences of the amino acids of MDH displays two significant phylo-genetic groups divergence that is closely linked to enzymes. Some eubacteria MDHs such as cherichia coli have significantly higher sequence identification with the eukaryotes’ mitochondrial enzymes (Gpb.sav.sk.,2020). On the hand, eubacteria like thermus flavus are strongly associated with cytoplasmic and chloroplasts enzymes. Mito

In tertiary and quaternary structure, malate dehydrogenases from pig’s heart cytoplasm and mitochondria and other organisms MDHs have homologous sites that are active, coenzymes binding sites, not to mention quaternary structure (Gpb.sav.sk.,2020). In other words, malate dehydrogenase is similar to dimers in terms of stability, meaning a significant relationship between protein stability and enzymatic reaction. Every subunit has duo structurally and functionally differentiated domains.

References

Gpb.sav.sk. (2020). Retrieved 21 October 2020, from http://www.gpb.sav.sk/2002_03_257.pdf.

Isralewitz, B., Gao, M., & Schulten, K. (2001). Steered molecular dynamics and mechanical functions of proteins. Current opinion in structural biology, 11(2), 224-230.

Takahashi-Íñiguez, T., Aburto-Rodríguez, N., Vilchis-González, A. L., & Flores, M. E. (2016). Function, kinetic properties, crystallization, and regulation of microbial malate dehydrogenase. Journal of Zhejiang University-SCIENCE B, 17(4), 247-261.