Amino Acids: The Lego Blocks of Plant Proteins

Proteins are chains of up to hundreds of amino acids linked together via peptide bonds and are encoded in DNA.

Similar to an alphabet forming words, the sequence of these amino acids can vary greatly, thereby producing a multitude of different proteins with different functions.

There are 22 standard amino acids, nine of which are considered essential to humans. Plants and micro-organisms can synthesize amino acids themselves, but new research has shown they benefit from additional supplementation. Amino acids are primarily categorized according to their polarity and pH.

They are designated L or D, depending on the arrangement of their atoms. An L-amino acid is the mirror image of a D-amino acid. Think of human hands. The left hand is the mirror image of the right hand.

This is an example of chirality and important in a discussion of amino acids. Plants only use L-amino acids (they only shake with their left hand) while D-amino acids are their mirror image and are only used by certain bacteria and fungi.

Amino acids are all similar. They have a nitrogenous group and a carboxylic acid group around a central carbon atom. They are differentiated from one another by their unique side chains. The chemical structure has potential for both positive and negative charge, which enables amino acids to participate in chemical reactions.

They are both pH and temperature dependent. Proteins denature when exposed to high heat or extreme pH. This coagulation is one of the main reasons most life cannot exist at these extremes.

Recent studies on advanced flowering plants have demonstrated amino acids to be excellent chelating agents. Chelators can form complexes with metallic ions, rendering them more soluble than if they were by themselves.

Slightly insoluble fertilizer components, such as iron, calcium and silica, have previously used chemical chelating agents to enhance their availability in fertilizer solutions. Amino acids are a natural and more effective alternative to these abrasive chelators.

Once the amino acids transport the target molecule into the plant’s transpiration stream, it can be used by the plant to make proteins—no chemical leftovers. Now let’s get into a brief summary of the 22 standard amino acids and their relation to the plant world:

Alanine (Ala)

• Found in antibiotics and in the cell walls of bacteria

Arginine (Arg)

• Used by plants to deter herbivores
• Possesses more nitrogen than any other amino acid
• A main component of histones (proteins that pack DNA into the nucleus of plant cells)
• Most common amino acid in cotyledons (seedling leaves)
• Integral to several important plant alkaloids

Asparagine (Asn)

• As reflected in the name, asparagine was first isolated from asparagus
• Found in largequantities in legumes, with a possible role in nitrogen fixation

Aspartic Acid (Asp)

• A component of important enzymes that build resistance to pathogens
• Plays an important role in apoptosis (programmed cell death) to kill off infected cells
• Involved in the synthesis of Adenosine triphosphate, the energy currency of plant cells
• A close chemical relative of aspartame

Cysteine (Cys)

• Contains sulfur that gives it the ability to form disulfide bonds, which increases the strength of an amino acid chain
• A component of iron-sulfur proteins, a part of the electron transport chain in photosynthesis

Glutamic Acid (Glu)

• Forms enzymes and other proteins and plays a role in amino acid signaling mechanisms
• The salt form is the flavor enhancer monosodium glutamate

Glutamine (Gln)

• Used as an alternate source of energy and nitrogen
• Brassica and legumes contain heaps of it

Glycine (Gly)

• The simplest amino acid
• Used in herbicides
• Its presence has been confirmed in space, giving promise to the possibility of extraterrestrial life

Histidine (His)

• Involved in the growth and development of plants and in acid-base chemistry
• Helps plants tolerate heavy metals

Isoleucine (Ile)

• Stimulates plant immune systems and defense mechanisms against pathogens and herbivores

Leucine (Leu)

• Involved in plant disease resistance and immunity
• The most common amino acid on Earth

Lysine (Lys)

• Involved in a plant’s responses to changes in the environment
• Plays a plant reproductive role
• Involved in genetic expression and DNA structure (another component of histones)

Methionine (Met)

• Contains sulfur
• Used to synthesize the natural plant hormone ethylene by way of the yang cycle
• Found in seeds in large quantities

Phenylalanine (Phe)

• An important part of plant metabolism

Proline (Pro)

• The nitrogen ring in the molecular structure contains strong bonds that provides the molecule rigidity that can withstand extremes in the environment

Pyrrolysine (Pyl)

• Most recently discovered amino acid
• Found only in bacterial enzymes

Selenocysteine (Sec)

• Like cysteine, but with selenium instead of sulfur
• Forms unique enzymes with selenium, giving it catalytic properties

Serine (Ser)

• First found in silk and named after the Latin word for silk, sericum
• Precursor to folic acid (vitamin B₉)

Threonine (Thr)

• Forms enzymes that deter insect herbivores

Tryptophan (Trp)

• Responsible for many floral scents and used in perfumes
• Precursor to important biomolecules such as serotonin, niacin and auxins
• The amino acid in your turkey dinner on Thanksgiving that makes you tired

Tyrosine (Tyr)

• Integrated in the structure of some plant phytohormones
• Enzymes important for plant defense against environmental stresses

Valine (Val)

• A component of some plant antibiotics that fight pathogens