How a Scientist Solved the Mystery of a Plant Enzyme
Have you ever wondered why a fresh fig feels so tender, or why it was historically used to tenderize tough meats? The secret lies in a powerful, proteolytic enzyme—a molecular protein-scissor—called ficin. For years, scientists knew this enzyme was incredibly potent, but it presented a curious puzzle: inside the unbroken fruit, it was dormant. How did this sleeping giant wake up? In the mid-20th century, a scientist named Theodore Winnick decided to find out, and his elegant experiments not only solved the mystery but also provided a masterclass in how life controls its most powerful tools.
Found naturally in fig latex
Breaks down other proteins
Stored in inactive form
To appreciate Winnick's work, we first need to understand enzymes. Think of your body—or a fig—as a bustling chemical factory. Thousands of reactions are happening every second, from digesting food to building new tissue. Enzymes are the specialized workers in this factory. They are proteins that speed up (catalyze) specific chemical reactions without being used up themselves.
Each enzyme has an "active site," a unique shape that fits only its specific target molecule (the "key"). When the key fits, the enzyme gets to work.
Now, imagine an enzyme whose job is to chop up other proteins. This is incredibly useful for digestion but incredibly dangerous if it's active in the wrong place or time. If these "molecular scissors" were always active, they would digest the very cells that made them!
This is the central problem with enzymes like ficin. They are produced in an inactive form, known as a proenzyme or zymogen. They are the factory workers delivered in a soundproof, locked box. Only when they reach the correct location—like your stomach for digestive enzymes, or a wound site in a fig—do they get "activated."
Theodore Winnick and his colleagues at the University of Buffalo set out to discover what specific trigger was needed to unlock ficin's power. Their hypothesis was that a small, specific change to the inactive proenzyme would be the key.
Winnick's approach was methodical and clever. He extracted the inactive precursor of ficin from the latex of figs and then subjected it to various potential activating conditions.
He carefully collected the milky sap (latex) from figs, which contained the inactive pro-ficin.
He separated the pro-ficin from other components in the sap to ensure a clean starting material.
He divided the purified pro-ficin into several samples and exposed each to a different potential activating agent.
After each treatment, he measured the resulting enzyme activity by testing how quickly it could break down a standard protein substrate. A large increase in activity meant he had found the key.
Collecting fig latex containing inactive pro-ficin
Isolating pro-ficin from other components
Applying different potential activators
Quantifying enzyme activity after treatment
The results were clear and definitive. The only treatments that successfully activated pro-ficin were the reducing agents, most notably cysteine.
| Treatment Applied to Pro-Ficin | Resulting Ficin Activity | Conclusion |
|---|---|---|
| Cysteine (Reducing Agent) | Very High | Successful activation. |
| Glutathione (Reducing Agent) | High | Successful activation. |
| Hydrogen Peroxide (Oxidizer) | None | No activation. |
| Papain (Another Enzyme) | Very Low / None | Not the primary activation mechanism. |
| Mild Acid | Low | Minor effect, not the main trigger. |
| Mild Alkali | Low | Minor effect, not the main trigger. |
This table shows the dramatic increase in protein-digesting power after activation with cysteine, measured by the release of broken-down protein fragments over time.
| Time (Minutes) | Protein Digested by Inactive Pro-Ficin (units) | Protein Digested by Cysteine-Activated Ficin (units) |
|---|---|---|
| 10 | 0.5 | 25.0 |
| 20 | 1.0 | 48.5 |
| 30 | 1.4 | 72.0 |
Winnick didn't stop there. He analyzed the chemical reaction and found that activation was not a one-way street. If he took the activated ficin and exposed it to an oxidizing agent, he could re-form the disulfide bridge and deactivate the enzyme.
| Step | Treatment | State of Enzyme | Activity Level |
|---|---|---|---|
| 1 | None | Pro-Ficin | Inactive |
| 2 | Add Cysteine (Reduces -S-S-) | Active Ficin | High |
| 3 | Add Oxidizer (Reforms -S-S-) | Inactive Ficin | Low |
This reversible switch was a beautiful demonstration of precise biological control. The fig could keep its ficin safely stored, and a subtle chemical shift in the environment—like the more "reducing" conditions found in a wound—could instantly mobilize its defensive enzyme.
Theodore Winnick's work was far more than an esoteric study of a fig enzyme. It was a brilliant piece of biochemical detective work that revealed a fundamental principle of life: power must be controlled. The simple disulfide switch he identified in ficin is a common regulatory mechanism used across the living world.
Understanding how to activate and control ficin paved the way for its commercial and scientific use. Today, ficin is used in food processing to tenderize meat, in cheese production, and even in the laboratory to study other proteins.
Winnick's findings provided insights into enzyme regulation that extend far beyond ficin. The disulfide switch mechanism is now recognized as a common regulatory strategy in biochemistry.
So, the next time you enjoy a perfectly tender piece of meat or marvel at the complexity of a biological process, remember the sleeping giant in the fig and the scientist, Theodore Winnick, who discovered the key to waking it up.
This article is based on the seminal work of Theodore Winnick, particularly his 1950s publications such as "On the Mechanism of Ficin Activation" in the Journal of Biological Chemistry.