"Being decomposed without a sound."
Kana watched the starch decomposition experiment.
Milia nodded. "Amylase is working."
"Invisible, but certain."
Rei added reagent. "Iodine reaction. If blue color disappears, it's proof starch was decomposed."
The color faded.
"Amazing," Kana was impressed. "We didn't add anything."
"We added enzyme," Milia corrected.
"But the enzyme itself doesn't change?"
"Because it's a catalyst," Rei explained. "Promotes reaction but isn't consumed itself."
Kana thought. "How?"
Milia showed a model. "The substrate, starch, binds to the enzyme's active site."
"Lock and key."
Rei supplemented. "More precisely, induced fit model."
"The keyhole deforms slightly to match the key's shape."
Kana was surprised. "It's flexible."
"Proteins are dynamic structures," Milia said.
"Not completely fixed. They fluctuate."
Rei continued explaining. "When substrate binds, enzyme shape optimizes."
"That accelerates the reaction."
Kana wrote in her notebook. "Shape change → reaction promotion."
"But why only specific substrates?"
Milia answered. "Substrate specificity."
"Amylase decomposes starch. But not proteins."
Rei added. "If active site shape and substrate shape don't match, they can't bind."
"Molecular recognition."
Kana proposed an experiment. "I want to try with a different substrate."
Milia prepared cellulose. "This also has similar structure to starch."
Added to test tube. Even after time passed, no change.
"Why?" Kana was surprised.
Rei compared structural formulas. "Starch is α-glucose bonds. Cellulose is β-glucose bonds."
"Slightly different stereochemistry."
Milia supplemented. "Enzymes distinguish that small difference."
"Too precise," Kana was moved.
"Characteristic of life," Rei said. "Molecular-level precision."
Milia took out another enzyme. "Cellulase. Cellulose-decomposing enzyme."
Added it, and this time reaction occurred.
"Change the enzyme, change the substrate."
Kana summarized. "One enzyme, one job."
"Efficient," Rei acknowledged.
"But the body has thousands of enzymes."
Milia explained. "Each handles a specific reaction."
"Metabolic pathways are enzyme relays."
Kana asked. "Without enzymes?"
"Reactions don't happen. Or are extremely slow," Rei answered.
"At room temperature, many biochemical reactions don't proceed naturally."
Milia gave an example. "Protein decomposition. Without enzymes, takes years."
"With enzymes, seconds."
Kana was surprised. "Hundreds of millions times faster?"
"Yes. That's enzyme power."
Rei supplemented. "Lowers activation energy."
"Lowers the reaction barrier."
Kana thought. "But why don't enzymes break?"
"Because they're catalysts," Milia answered. "After reaction, return to original form."
"Can be used repeatedly."
Rei added. "However, if conditions are good."
"At high temperature or extreme pH, they denature."
Kana understood. "That's why body temperature and blood pH are constant."
"To protect enzymes."
Milia nodded. "Life maintains optimal environment for enzymes."
"Homeostasis."
Rei said finally. "Enzymes work silently."
"Don't assert themselves. But without them, life stops."
Kana stared at the test tube. "Invisible workers."
Milia smiled. "Unsung heroes."
"But the stars of life."
The three began cleaning up.
Outside the window, the sun was setting. Enzymes continue working quietly in the body even now.