"It won't react with enzyme alone..."
Toma stared at the test tube with a puzzled expression.
Milia approached. "Did you add coenzyme?"
"Coenzyme?"
Rei explained. "Small molecules that help enzymes. Many enzymes don't function with just protein."
Kana opened her notebook. "There are helpers."
"Yes. Enzyme is the main role, but the stage can't work without backstage crew."
Milia took out a small bottle. "This is NAD+. One of the most important coenzymes."
"Nad?" Toma asked back.
"Nicotinamide adenine dinucleotide," Rei gave the formal name.
"Long..."
"But the role is clear. It carries electrons."
Kana became interested. "Carries electrons?"
Rei drew a diagram. "In redox reactions, it accepts electrons from substrate, becoming NADH."
"Changes to NADH?"
"Yes. Reduced form. Later in another reaction, it gives electrons and returns to NAD+."
Milia added. "So NAD+ and NADH circulate in cells. Electron shuttle bus."
Toma understood. "It's recycled."
"Exactly. Small amount of NAD+ can mediate vast reactions."
Kana asked. "Are there other coenzymes?"
Rei enumerated. "FAD, CoA, many B vitamins..."
"Vitamins?"
"Yes. Many vitamins are coenzyme precursors. So deficiency stops metabolism."
Milia said with serious expression. "Beriberi is vitamin B1 deficiency. Can't produce coenzyme thiamine pyrophosphate."
"Without coenzyme, disease occurs?"
"Yes. Sugar metabolism is blocked, neurological symptoms appear."
Toma thought. "So coenzymes are subtle but super important."
"Perfect understanding," Rei smiled.
Kana wrote on the whiteboard. "Besides coenzymes, other helpers?"
"Cofactors," Milia answered. "Like metal ions."
"Metals?"
Rei explained. "Zinc, iron, copper, magnesium... many enzymes require metal ions."
"Why need metals?" Toma asked.
"Electron transfer, substrate activation, structural stabilization," Rei listed.
Milia gave example. "Hemoglobin contains iron. Iron binds oxygen."
"I see."
"Catalase uses iron, superoxide dismutase uses copper and zinc."
Kana was impressed. "Life uses diverse elements from periodic table."
"Yes," Rei nodded. "Not just carbon, hydrogen, oxygen, nitrogen. Trace elements are essential too."
Toma added coenzyme to the test tube. "Now the reaction should proceed."
The liquid gradually began changing color.
"It's working!" Kana rejoiced.
Milia said quietly. "Invisible, but NAD+ is carrying electrons."
"Nameless hero," Toma murmured.
Rei supplemented. "Not nameless. They have proper names. But spotlight falls on enzymes."
"Beauty of supporting roles," Kana smiled.
Milia said seriously. "But without supporting roles, main role can't shine. Biochemistry is concerto."
"Everyone is important," Toma nodded.
Rei finally added. "In cells, thousands of reactions proceed simultaneously. Each involves cooperation of enzyme, coenzyme, and cofactor."
"An orchestra," Kana said.
"Exactly. And the conductor is genes."
Milia looked outside the window. "Life's complexity arises from countless cooperations."
Toma shook the test tube. "In here too, invisible cooperation exists."
"Always exists," Rei said quietly. "In biochemistry's shadow, nameless molecules continue working."
Kana closed her notebook. "Which coenzyme should we investigate next?"
The four moved toward the next experiment. To know more about the unsung heroes.