Chapter 2. Plants Serve Up Useful Enzymes

Plants Serve Up Useful Enzymes

Read the article below. Then complete the comprehension questions that follow.

Unripe papayas are the source of papain, which is used as a digestive aid.

Biodiversity yields medicinal compounds

The biodiversity of the plant world has provided us with fascinating plant remedies. Some have been harnessed by traditional healers and native people for thousands of years. One such source is the papaya.

Papayas grow in bundles on lush, tropical trees. When yellow and ripe, they are a delicious treat. Yet it’s the green, unripe fruit that is harvested for its potent enzyme content. When shallow cuts are made on the neck of an unripe papaya, a thick milky substance called latex slowly seeps out. This latex is collected, purified, and dried to make powdered papain.

Papain is marketed as a dietary supplement—primarily for use as a digestive aid. It eats away at proteins and helps break down food in your stomach. (See the box below that describes other uses of papain.) It belongs to a class of plant-derived medicinal compounds called cystiene proteases. As we will learn, these help the body digest food and also can be found in kiwi and pineapple.

How cysteine proteases work

Papain is a superfamily of proteases—a special class of enzymes that break down the peptide bonds that hold proteins together. Papain is a “cysteine protease hydrolase” enzyme, which means the active site contains a cysteine molecule. It’s this cysteine molecule which helps breaks down peptide bonds.

Bromelain is the family of cysteine proteases extracted from pineapple. It is usually prepared from cooled pineapple juice, and—like papain—is sold as a digestive aid.

The science behind traditional plant medicine

Papaya and pineapple have been used by native healers for a very long time. In South America, papaya extract is still used to treat stings from jellyfish, stingrays, bees, wasps, and mosquitoes. It can help breakdown proteins in the toxins. Studies have recently shown that both papain and bromelain can have anti-inflammatory benefits.

Bromelain, which comes from pineapples, is another type of cysteine protease.

Much of the information we have about plant medicines like pineapple and papaya extract come from interviews with native healers. This means plant preparations are often based on tradition rather than clinical trials and scientific methodology. But in the case of papain and bromelain, there are also a few clinical studies supporting health benefits—although only to a limited extent. There is a larger body of preclinical and biochemical research that shows how these enzymes function. From cancer treatment to the absorption of antibiotics, several applications are being explored for cysteine protease enzymes—especially those from pineapple.

Are they safe?

There are no concerns about the use of papain as a meat tenderizer or digestive aid, yet the United States Food and Drug Administration (FDA) is concerned about its use in over-the-counter topical medications. These concerns include the possibility of vision loss (from using eye drops and contact solutions that contain papain). In addition, people with latex allergies may also develop allergic reactions to the topical use of papain.

Like papain, bromelain is generally regarded as safe by the FDA. Yet whenever you purchase medicinal plant extracts—an especially when you mix them with prescription or over-the-counter drugs—it’s best to first check with a doctor.

© 2015 WH Freeman and Company

2.1 Comprehension Questions

Answer the following questions to demonstrate your understanding of the article.

Question 2.10

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Correct.

Incorrect.