We will see that the vastly complex characteristics of even a small, relatively simple, protein are a composite of the properties of the amino acids which comprise the protein. Top Essential amino acids Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in degradation of the body's proteins—muscle and so forth—to obtain the one amino acid that is needed.
Unlike fat and starch, the human body does not store excess amino acids for later use—the amino acids must be in the food every day. The 10 amino acids that we can produce are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.
Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well. Authors Authors and affiliations Masato Ikeda.
Chapter First Online: 13 November Keywords Amino acid Fermentation Metabolic engineering Transport engineering Corynebacterium glutamicum Genome information. This is a preview of subscription content, log in to check access.
In: Roehr M ed Biotechnology, 2nd edn, vol. Sikyta B Methods in industrial microbiology. Ellis Horwood, Chichester Google Scholar. In: Stephanopoulos G ed Biotechnology, 2nd edition, vol. Yamane T, Shimizu S Fed-batch techniques in microbial processes. Amino acids are made from plant-derived ingredients. Fermented products such as miso and soy are made by fermenting soy or wheat with a koji culture.
The fermentation process breaks down the protein and turns it into amino acids. Miso and soy are examples of how amino acids have long been part of the Japanese diet and how Japanese people tried to create delicious food. The amino acids used in amino acid products are mainly made by fermenting plant-derived ingredients in the same way that miso and soy sauce are made. In amino acid fermentation amino acids are made by fermenting ingredients with microorganisms like probiotic bacteria.
These microorganisms turn the ingredients into food and other substances that are needed by the microorganisms. In fermentation ingredients such as molasses are added to a medium that cultivates microorganisms.
This helps the microorganisms multiply and make amino acids. Microorganisms contain enzymes that accelerate reactions to break down and synthesize new substances The fermentation process is a series of reactions involving around 10 to 30 types of enzymes. To make amino acids using microorganisms, we first have to find microorganisms that have a strong potential for making amino acids.
One gram of natural soil contains about million microorganisms. From this, we have to then find which microorganisms are most effective. When the right microorganism is found, better strains of it must be developed to get microorganisms with the best potential. The amount of amino acids made depends on the quantity and quality of enzymes. Aside from their role in composing proteins, amino acids have many biologically important functions.
They are also energy metabolites, and many of them are essential nutrients. Amino acids can often function as chemical messengers in communication between cells. For example, Arvid Carlsson discovered in that the amine 3-hydroxytyramine dopamine was not only a precursor for the synthesis of adrenaline from tyrosine, but is also a key neurotransmitter.
Certain amino acids — such as citrulline and ornithine, which are intermediates in urea biosynthesis — are important intermediaries in various pathways involving nitrogenous metabolism. Although other amino acids are important in several pathways, S-adenosylmethionine acts as a universal methylating agent.
What follows is a discussion of amino acids, their biosynthesis, and the evolution of their synthesis pathways, with a focus on tryptophan and lysine.
Figure 1: Major events in the evolution of amino acid synthesis The way amino acids are synthesized has changed during the history of Earth.
The Hadean eon represents the time from which Earth first formed. The subsequent Archean eon approximately 3, million years ago is known as the age of bacteria and archaea. The Proterozoic eon was the gathering up of oxygen in Earth's atmosphere, and the Phanerozoic eon coincides with the major diversification of animals, plants, and fungi. In a flask, they combined ammonia, hydrogen, methane, and water vapor plus electrical sparks Miller They found that new molecules were formed, and they identified these molecules as eleven standard amino acids.
From this observation, they posited that the first organisms likely arose in an environment similar to the one they constructed in their flask, one rich in organic compounds, now widely described as the primordial soup.
This hypothesis is further extended to the claim that, within this soup, single-celled organisms evolved, and as the number of organisms increased, the organic compounds were depleted. Necessarily, in this competitive environment, those organisms that were able to biosynthesize their own nutrients from elements had a great advantage over those that could not.
Today, the vast majority of organic compounds derive from biological organisms that break down and replenish the resources for sustaining other organisms. And, rather than emerging from an electrified primordial soup, amino acids emerge from biosynthetic enzymatic reactions.
As implied by the root of the word amine , the key atom in amino acid composition is nitrogen. The ultimate source of nitrogen for the biosynthesis of amino acids is atmospheric nitrogen N 2 , a nearly inert gas.
However, to be metabolically useful, atmospheric nitrogen must be reduced. This process, known as nitrogen fixation, occurs only in certain types of bacteria. This bond is extremely difficult to break because the three chemical bonds need to be separated and bonded to different compounds.
Nitrogenase is the only family of enzymes capable of breaking this bond i. These proteins use a collection of metal ions as the electron carriers that are responsible for the reduction of N 2 to NH 3. All organisms can then use this reduced nitrogen NH 3 to make amino acids. In humans, reduced nitrogen enters the physiological system in dietary sources containing amino acids. All organisms contain the enzymes glutamate dehydrogenase and glutamine synthetase, which convert ammonia to glutamate and glutamine, respectively.
Amino and amide groups from these two compounds can then be transferred to other carbon backbones by transamination and transamidation reactions to make amino acids. Interestingly, glutamine is the universal donor of amine groups for the formation of many other amino acids as well as many biosynthetic products. Glutamine is also a key metabolite for ammonia storage.
They are distinguished from one another primarily by , appendages to the central carbon atom. Figure 2 Figure Detail In the study of metabolism, a series of biochemical reactions for compound synthesis or degradation is called a pathway. Amino acid synthesis can occur in a variety of ways. For example, amino acids can be synthesized from precursor molecules by simple steps.
Alanine, aspartate, and glutamate are synthesized from keto acids called pyruvate, oxaloacetate, and alpha-ketoglutarate, respectively, after a transamination reaction step. Similarly, asparagine and glutamine are synthesized from aspartate and glutamate, respectively, by an amidation reaction step. The synthesis of other amino acids requires more steps; between one and thirteen biochemical reactions are necessary to produce the different amino acids from their precursors of the central metabolism Figure 2.
The relative uses of amino acid biosynthetic pathways vary widely among species because different synthesis pathways have evolved to fulfill unique metabolic needs in different organisms. Although some pathways are present in certain organisms, they are absent in others. Therefore, experimental results about amino acid metabolism that are achieved with model organisms may not always have relevance for the majority of other organisms.
Not all the organisms are capable of synthesizing all the amino acids, and many are synthesized by pathways that are present only in certain plants and bacteria. Mammals, for example, must obtain eight of twenty amino acids from their diets. This requirement leads to a convention that divides amino acids into two categories: essential and nonessential given a certain metabolism.
Because of particular structural features, essential amino acids cannot be synthesized by mammalian enzymes Reeds Nonessential amino acids, therefore, can be synthesized by nearly all organisms. The loss of the ability to synthesize essential amino acids likely emerged very early in evolution, because this dependence on other organisms for the source of amino acids is common among all eukaryotes, not just those of mammals.
How do certain amino acids become essential for a given organism? Studies in ecology and evolution give some clues. Organisms evolve under environmental constraints, which are dynamic over time. If an amino acid is available for uptake, the selective pressure to keep intact the genes responsible for that pathway might be lowered, because they would not be constantly expressing these biosynthetic genes.
Without the selective pressure, the biosynthetic routes might be lost or the gene could allow mutations that would lead to a diversification of the enzyme 's function. Following this logic, amino acids that are essential for certain organisms might not be essential for other organisms subjected to different selection pressures.
For example, in , Ishikawa and colleagues completed the genome sequence of the endosymbiont bacteria Buchnera , and in it they found the genes for the biosynthetic pathways necessary for the synthesizing essential amino acids for its symbiotic host, the aphid.
Interestingly, those genes for the synthesis of its "nonessential" amino acids are almost completely missing Shigenobu et al. In this way, Buchnera provides the host with some amino acids and obtains the other amino acids from the host Baumann ; Pal et al. Free-living bacteria synthesize tryptophan Trp , which is an essential amino acid for mammals, some plants, and lower eukaryotes.
The Trp synthesis pathway appears to be highly conserved, and the enzymes needed to synthesize tryptophan are widely distributed across the three domains of life. This pathway is one of three that compose aromatic amino acids from chorismate Figure 2, red pathway. The other amino acids are phenylalanine and tyrosine. Trp biosynthetic enzymes are widely distributed across the three domains of life Xie et al. The genes that code for the enzymes in this pathway likely evolved once, and they did so more recently than those for other amino acid synthesis pathways.
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