In this post I hope to review the basics of enzymes and their application to laundry detergents, products that we (hopefully) use often. One of the first things I did in preparation for this blog was look at the ingredients in my own laundry detergent, all® small & mighty with stainlifters.
I looked at the list of ingredients on the back and….. I was very disappointed. “Cleaning agents (anionic and non ionic surfactants), buffering agent, stabilizer and brightening agent.”
Anyway, there are some laundry detergents that use enzymes, including Tide, Arm and Hammer, and Ultra Plus, which you can read about here. So what kind of enzymes are used in laundry detergents? They typically include proteases, lipases, and amylases . Some detergents also include cellulases and peroxidases, which remove soil and brighten colors, respectively. The list below was modifed from this paper if you want to read more.
Protease: Breaks down protein. Common protein stains include blood, sweat, egg, and grass.
Lipase: Breaks down lipid, AKA fat. Common stains are from butter, oil, and salad dressing.
Amylase: Breaks down starch-based residues found in food such as spaghetti, custard, chocolate, gravy, and potatoes.
Cellulase: Removes soil indirectly by breaking down cellulose. Used on cotton fabric, as it does not break down the cotton fibers.
Peroxidase: Bleaches dye that is released from fabric to prevent bleeding onto other fabric.
Before we discuss how proteases, lipases, amylases, etc. do their thing, let’s talk about enzymes in general. For all the reactions described above, energy is required. The more energy required, the slower the rate in which it proceeds. What enzymes do is reduce the energy required for the reaction to occur. For example, a protease reduces the energy input needed to break down a protein. Once the enzyme is added, the energy needed is lower, allowing the rate of the reaction to proceed. It’s kind of like having a sherpa with you when you climb Mount Everest.
Another important fact about enzymes is that once a reaction is done, the enzyme is still available to catalyze another one. In other words, a protease molecule can break down more than one protein. This is one of the main reasons why only a small amount of enzyme is needed to make a big effect in laundry detergent, something that producers definitely like.
Other reasons why laundry detergent companies like enzymes are
- they are cheap
- they have specific actions
- they send less organic pollutants into the water
- they are non-corrosive
Enzymes are relatively cheap because they can be made easily in large quantities, as long as you know a little about genetics and cell culture. Enzymes are “made” by growing cells that are known to produce a lot of the enzyme of interest. The types of cells often used are yeast, bacteria, or fungi. Once the cells have grown, they can be broke open and the enzyme you want can be isolated. Scientists have improved upon this method by altering the cells’ genome, causing the cells to grow abnormally high amounts of the enzyme desired.
A suitable enzyme for use in laundry detergents must also have the following characteristics:
- compatibility with detergents (the actual detergent in “laundry detergent” can denature proteins, as we talked about last week in The Incredible Edible Egg. Since enzymes are proteins, they must be resistant to the detergents used to clean fabric)
- must work at a variety of temperatures
- must be stable at a pH range from 8 to 10.5
The ability of enzymes to work at a variety of temperatures, especially low temperatures, makes laundry detergent more environmentally-friendly. It also can replace old ingredients used in laundry detergents that are harmful to the environment.
Let’s select protease and lipase to see how they work.
Since we talked about eggs last week, lets pretend you got egg white on your shirt. The main protein in egg whites is albumin. So how does a protease break down albumin? Most commercially used enzymes are alkaline serine proteases (see this paper for a review about alkaline proteases). Serine proteases use 3 amino acids that work as the Three Musketeers also known as the catalytic triad to break bonds in albumin.
- The protease and albumin bind, forming a Michaelis complex. The portion of albumin binding to the protease is shown in red.
- Serine (Ser 195) from the enzyme attacks a bond in the protein albumin which connects its subcomponents, or amino acids, together. This attack causes the formation of a tetrahedral intermediate.
- The tetrahydral intermediate changes into an acyl-enzyme intermediate due to general acid catalysis from histidine (His 57). The albumin bond has been broken, but albumin is still bound to the protease.
- One part of the broken albumin protein is released.
- The acyl-enzyme intermediate is deacetylated, forming a second tetrahedral intermediate.
- The other half of the broken albumin protein is released. The protease is left in its original form.
Once you finally got that egg stain off your shirt, you had to be a klutz and smear some butter on it. What would you use to remove butter? Butter has a high amount of lipids called triacylglycerol, so a lipase would be a good enzyme to use.
Berg JM, Tymoczko JL, & Stryer L. (2002) Biochemistry. 5th Ed. W.H. Freeman: New York, NY.
It is crazy to think that all of this is going on every time you run a load of laundry. Pretty sweet! As a reward for getting through all of these boring diagrams, here are some awesome pictures and video that won the 2011 International Science and Engineering Photo Challenge.
Metabolomic Eye, Bryan W. Jones (Photography – 1st Place)
Science 3 February 2012: Vol. 335 no. 6068 pp. 526-527
The Ebola Virus, Ivan Konstantinov et al. (Informational Posters & Graphics – Honorable Mention)
Science 3 February 2012: Vol. 335 no. 6068 pp. 530-531
BTW, getting the Ebola virus is my worst fear. Ever. But it sure looks cool!
Powers of Minus Ten, Laura Lynn Gonzalez (Interactive Games – Honorable Mention)
Science 3 February 2012: Vol. 335 no. 6068 pp. 532-533
Well, I hope you have a great day! I am off to play Powers of Minus Ten. 🙂