"Already digested after breakfast?"
Kana pressed her stomach curiously.
Rei answered. "Amylase, pepsin, lipase... many enzymes are working."
"That fast?"
"Enzymes are catalysts. They dramatically accelerate reactions."
Toma asked. "How much?"
"Depending on the enzyme, 10^6 to 10^17 times."
Kana was surprised. "Over a hundred million times?"
"Catalase exceeds 10^7. Decomposes over a million hydrogen peroxide molecules per second."
Toma took notes. "Turnover number, kcat."
"Yes. Number of substrate molecules one enzyme molecule can convert per second."
Rei continued. "But speed isn't everything. Specificity is also important."
"Specificity?" Kana asked.
"Recognizes only specific substrates. Lock and key."
Toma asked. "Why only specific molecules?"
"Active site shape is complementary to substrate shape."
Rei drew a diagram. "Fischer's lock and key model. But reality is more dynamic."
"Dynamic?"
"Induced fit model. When substrate binds, enzyme shape changes."
Kana understood. "Active site adjusts to the substrate?"
"Yes. Achieves optimal configuration."
Toma looked at his notes. "Transition state stabilization?"
"That's the core," Rei emphasized. "Enzymes preferentially stabilize the transition state."
"Transition state?"
"During reaction, the highest energy state."
Kana took notes. "Lowers activation energy?"
"Exactly. Lowering transition state energy increases reaction rate."
Rei continued. "Active site amino acids are precisely positioned."
Toma asked. "How?"
"Using hydrogen bonds, electrostatic interactions, covalent bonds... diverse interactions."
Kana asked. "Cofactors involved too?"
"Required for many enzymes. NAD+, FAD, coenzyme A."
Rei explained. "Enable chemical reactions that proteins alone cannot do."
Toma murmured. "Molecular cooperation."
"Yes. Enzymes are orchestra conductors."
Kana thought. "But isn't too fast problematic?"
"There are control mechanisms," Rei answered. "Allosteric regulation, feedback inhibition."
"Allosteric?"
"Regulatory molecules bind at sites other than the active site."
Toma took notes. "And activity changes?"
"Yes. Through structural changes, the active site is affected."
Rei continued. "For example, the final product of a metabolic pathway inhibits the first enzyme."
"Self-regulation?" Kana understood.
"Feedback inhibition. Prevents overproduction."
Toma asked. "Without enzymes?"
"Many reactions don't proceed at body temperature. Some would take hundreds of years."
Kana was moved. "Done in seconds instead."
"The speed of life is the speed of enzymes," Rei said.
Toma summarized in his notebook. "Specificity, efficiency, control. All three must work together."
"And tens of thousands of enzymes work in coordination."
Kana murmured. "A molecular storm while breakfast digests."
Rei smiled. "In the invisible world, catalytic reactions dance."
The three fell silent. Too fast morning, discovering enzyme wonders.