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Monday, October 25, 2010
Amino Acids-What you need to know
Every species of plant and animal has its own characteristic proteins. The proteins of closely related species are different. Indeed the proteins of different structures of the same organism are different. It has been estimated that there are 1600 different proteins in the human body. Similar complexity of protein constitution exists in the tissues of practically all animals. Each plant, also, possesses several different proteins in its makeup, each different tissue possessing its own characteristic protein. The proteins of the food supply are very different to those of the animal taking that food. These have to be broken down and reconverted into proteins peculiar to the eater. When protein digestion is completed the protein has been broken down into simpler compounds known as amino acids. These are organic acids containing nitrogen. It does not seem necessary that I here enter into any detailed and technical discussion of the complexities of their chemical constitution. This can be of no value to my lay readers and my professional readers may consult their text books and reference books to refresh their memories upon this subject.
Amino acids, called also, the "building stones of the body," are much talked about today. Indeed, it begins to look as though they are now to go through the same over-emphasis, high pressure consideration and commercial exploitation that the vitamins are just now beginning to emerge from. Already synthetic amino acids and amino acids extracted from food sources are offered for sale to the food-conscious public. These offers are accompanied with the usual misleading and unfounded claims for their superior virtues.
The body cannot absorb any protein as such. If protein is absorbed directly into the blood stream, without first undergoing the processes of digestion, it is poisonous. Proteins must be broken down into simpler compounds known as amino acids before they can be absorbed and assimilated. Introduce the amino acids out of which proteins are made and all is well.
Proteins are colloids--amino acids are crystalloids. Plant and animal material should or must be in the colloidal state. Each plant and animal, however, must build its own colloids and in order that the animal body may utilize the substances in plant colloids in building its own colloids, it must first break them down into crystalloids. While it is not entirely correct to speak of protein as containing such and such amino acids, for these are known to us only after the protein has been decomposed; still, for convenience we say proteins are made up of chemical units called amino acids, just as words are made up of letters. Just as the twenty-six letter of the alphabet are sufficient to form millions of words; so, the twenty-two or more amino acids are sufficient to form the many different proteins known and unknown. It is generally believed that there are amino acids that have not been isolated and identified.
Proteins are numerous, each one being different from every other. The protein molecule is exceedingly complex, containing from twelve to twenty different amino acids. Amino acids, themselves, are complex nitrogenous bodies, synthesized by plants in the process of growth. Animals are able only to analyze proteins in the process of digestion, and re-synthesize the resulting amino acids into new and different proteins.
There exists a certain amount of confusion in naming and classifying the amino acids. Berg names the following twenty-one: glycocoll, alanin, serin, valin, leucin, isoleucin, asparaginic acid, asparagin,glutamin, arginin, ornithin, lysin, cystin, cystein, B-phenylalanin,tyrosin, trytophan, histidin, prolin, and oxyprolin. Sherman lists the following twenty-two: glycine, alanine, valine,leucine, isoleucine, norleucine, phenylalanine, tyrosine, serine,theonine, cystine, methionine, aspartic acid, glutamic acid,hydroxyglutamic acid, argenine, lysine, histidine, proline,hydroxyproline, tryptophan and serine. Amino acids serve the following five general functions in the animal body:
- They serve as building stones out of which the proteins characteristic of the various cells of the body are synthesized. Thus,they serve as the materials of growth and repair.
- The cells use them in manufacturing the many and various enzymes of the body, in producing the various hormones and in producing other nitrogenous products. They are supposed to be employed in the production of genes and antibodies; but as these two "substances" are merely hypothetical entities, who knows.
- The blood proteins are made from the amino acids. These proteins, because of their colloidal osmotic pressure, are indispensable.
- They are said to be used as a source of energy. In this the nitrogen of the amino acid is regarded as being of little value. But when the amine has been split off from the amino acid the remainder of the molecule, which constitutes the larger part of it, contains no nitrogen,but much carbon. Thus, if they are not immediately needed, certain of the amino acids, such as glycine, alanine, cystine and arginine are transformed into glucose and glycogen.
- Some of the amino acids are supposed to serve certain specific functions. A deficiency of trytophan in young rats leads to cataract and blindness and to poor development of tooth enamel. In old as well as in young rats a lack of tryptophan causes blindness and impairs the generation of spermatozoa. Tryphtophan is essential to generation in rats. Tyrosine is thought to be essential to the production of the hormones adrenalin and thyroxin. A reduction of the number of spermatozoa is said to result from a deficiency of arganine.
ESSENTIAL AMINO ACIDS
The various amino acids are specific in their functions. They are not interchangeable. Of the twenty-two known amino acids only ten or twelve are regarded as essential or indispensable. Tryptophan, tyrosin, lysin, cystin, glutamic acid, histidin and ornathin are among the essential amino acids. If the diet supplies the essential amino acids in adequate quantities, growth, maintenance and reproduction are normal. If one or more of these is lacking or deficient this is not true. Examples: A deficiency of valine in the diet of young animals stunts growth and development to a remarkable degree. If lysin is lacking in the diet there is more or less maintenance but no growth. No matter how much protein and other elements supplied in the diet, if lysin and tryphtophan are lacking, life soon comes to an end.
It is held that the amino acids other than the ten or twelve indispensable ones can be made by the tissues from the essential amino acids, apparently by oxydizing them. Glycine apparently can be manufactured in the animal body from the other amino acids if it is lacking in the diet. Prolin, which may be readily produced in the body
by oxidation of histidin is, therefore, not considered an essential amino acid. Its production from histidin depends, however, upon an over supply of this latter acid. Glycocoll is also of such constitution that it may be produced in the body by the oxidation of several different amino acids. Casein of milk is devoid of glycocoll, but ratsfed upon casein thrive.
By an essential amino acid, then, is meant, one that the body cannot produce by oxidation (reduction) of another amino acid. The animal body cannot synthesize amino acids out of the elements of earth, air and water, but must receive these from the plant, which, alone, has the power to synthesize these substances. The animal body is capable only of producing some of the less complex amino acids out of the more complex ones by a reduction process.
Since the lower grade amino acids are formed within the body out of the higher compounds, they are regarded as of no vital importance. This, in my opinion, is a mistake. The body does seem to require them so that they are actually essential, even if it is not essential that they be taken in as such, but can be produced from other amino acids. On the other hand they can be produced from the higher amino acids only if these latter are present in excess of need. It may also be true that a saving of energy is secured if the lower grade amino acids are taken in with the food stuffs and the body is not compelled to reduce the higher compounds to lower grade. There is another theoretical possibility. The older theories of nutrition overlooked the universal validity of the Law of the Minimum to be explained in a later chapter. Investigators ignored the extent to which every tissue builder is dependent upon all the others. As Berg puts it: "They failed to realize that what is decisive for development, is not so much the absolute quantity of the various nutritive elements, as their relative proportions. They did not understand that the bodily need in respect of any one constituent of a diet can be determined only when we simultaneously take into account all the other factors of nutrition."There is the possibility that when one of the "non-essential" amino acids is lacking in the diet and the body is forced to make it from one of the essential amino acids, an actual reduction, below normal requirements, of the essential amino acid takes place with a corresponding lag in development.
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