Acid Phosphatase

Melody Clearwater's image for:
"Acid Phosphatase"
Image by: 

Biochemistry is one of today’s fastest growing fields in science today.  The study of Biochemistry helps us understand living organisms better by learning about metabolic pathways, how DNA works to make proteins, and about protein function.  The development and advancement of many different laboratory techniques help us learn about the chemical processes in organisms better.  In this article, I will discuss the importance of inorganic phosphate in the metabolic pathways of living organisms (specifically plants), how acid phosphatase helps plants obtain the inorganic phosphate they need, and some research projects studying acid phosphatase.

Inorganic phosphate is essential for plants to be able to utilize their energy.   The use of inorganic phosphate is much easier for plants to absorb than organic phosphate, due to its small size.  The small size of inorganic phosphate allows for easy transportation throughout the plant.  Inorganic phosphate may occur in the form of iron, aluminum, and calcium phosphate.  To mobilize these sources of phosphate, plant roots can excrete various organic acids, such as citrate. 

However, inorganic phosphate is one of least available nutrients in many ecosystems.  Although inorganic phosphate may not be readily available, plants are still able to utilize organic phosphate.  Different species of plants are able to use different mechanisms to convert organic phosphate into inorganic phosphate in their roots.  According to G. A. Gilbert in his article, Acid phospphatase activity in phosphorus-deficient white lupin roots, organic phosphate may account from 30% to 80% of available phosphate in agricultural soils.  To utilize this phosphate source, white lupin roots uses acid phosphatases to mobilize the phosphate.

 One of the main energy-carrying compounds that uses phosphate is called adenosine triphosphate, or ATP.  ATP is both used and produced in metabolic pathways in plants, such as glycolysis and the TCA cycle.  In glycolysis, glucose is converted into two molecules of pyruvate through several chemical reactions that produce several different intermediates as well as high energy compounds, such as ATP.  In the TCA cycle, the pyruvate from glycolysis is first converted into citrate and is then recycled to produce more ATP than glycolysis produces.

The use of ATP is important in many different processes in plants.  ATP can donate one or more of its three phosphates to the phosphorylation of proteins.  The phosphorylation of proteins, or the binding of inorganic phosphate to a protein, is an essential component of certain mechanisms, such as the transport of ions and molecules through cell membranes.  The phosphorylation of a protein causes the protein to change shape, allowing a temporarily bound ion or molecule to travel through the protein and into (or out of) the cell.  The phosphorylation of certain enzymes may also help them function.  Phosphorylation can cause the enzyme to expose an active site, allowing the enzyme to catalyze a desired reaction.

Now that I have covered the importance of phosphate in plants, I will now discuss how plants are able to utilize phosphate.  Acid phosphatase is an important enzyme that plants use to obtain their energy from phosphate.  Acid phosphatase’s function in plants is to hydrolyze phosphate esters during energy metabolism.  Phosphate esters are produced during glycolysis to help yield energy.

During initiation in glycolysis, glucose is converted into different phosphate esters through phosphorylation.  Once two ATP molecules have been used and fructose 1,6 bisphosphate has been produced, propagation occurs and different reactions help yield four ATP molecules.  Dephosphorylation of the phosphate esters is necessary to produce ATP.  Once the ATP molecules are produced, the plant can use them in other important processes, such as in active transport and the activation of enzymes.

 Because acid phosphatase is essential for plants to utilize their energy, plants also need an efficient method to store the acid phosphatase.  Due to its low pH, acid phosphatase needs to be stored away from proteins at risk of degradation.  To prevent any unwanted reactions between acid phosphatase and other proteins, acid phosphatase is stored in the lysosomes of cells, where the pH is optimal for the enzyme to reside in.  Acid phosphatase is also present in the roots of plants, where it can convert organic phosphate into inorganic phosphate so the plant will be able to utilize it.

Osmotic pressure is also important to study for acid phosphatase activity.  Salt concentrations in the soil effects how plant roots absorb nutrients.  A high salt concentration may affect the roots ability to absorb phosphate.  A lack of phosphate can prevent the plant from obtaining the energy it needs to grow and reproduce. 

Phosphorous is essential for living organisms to obtain the energy they need to survive.  Inorganic phosphorous can be bound to organic molecules, such as ATP, to help the plant carry out metabolic processes, participate in active transport to carry ions and large molecules through cell membranes, and allow enzymes to change shape to expose their active sites so it can catalyze reactions.  Due to its low pH, acid phosphatase needs to be stored in the lysosomes of cells, and is especially prominent in plant roots to aid in the uptake of phosphate from soil.  Further understanding of this enzyme is necessary to help us understand how to grow crop plants better.  Experiments determining the presence of feedback inhibition and the effects of osmotic pressure in plant roots can help us understand how to take care of plants better to help improve crop yields.  Any questions about acid phosphatase, as well as many other enzymes, can be answered through the growth and advancement of Biochemsitry.

More about this author: Melody Clearwater

From Around the Web