- WELCOME TO PROTEINS AND ENZYMES PART 11.
WE'LL LOOK A LITTLE MORE CLOSELY AT THOSE ENZYME COFACTORS.
AND LET'S GET STARTED.
ALL RIGHTY.
SO NOW LINGUISTICALLY, THERE ARE SOME INCONSISTENCIES
AS WE LOOK AT DIFFERENT TEXTBOOKS AND DIFFERENT PEOPLE
WE TALK WITH.
SO, I'LL START THIS OUT AS BEST I CAN FOR YOU.
SO ENZYME COFACTORS, RIGHT?
SO THAT'S A VERY BROAD TERM AND IT DESCRIBES CONJUGATED
PROTEINS THAT REQUIRE NON- PROTEINS PORTIONS AS COFACTORS,
SO ENZYMES THAT NEED COFACTORS.
WHEN WE THINK ABOUT THE ENZYME, RIGHT?
THAT'S THE PROTEIN PART.
SO THESE COFACTORS ARE NON-PROTEIN PORTIONS.
SO COFACTORS COME IN TWO FLAVORS.
THEY CAN BE METAL IONS.
AND WHAT I'VE OBSERVED IS IN--
WHEN I READ FROM DIFFERENT SOURCES,
COFACTORS SEEMS TO BE THE TERM THAT GOES WITH THE METAL IONS
THAT ARE USED TO AS PART OF AN ENZYME TO CATALYZE REACTIONS.
AND THEN, COENZYME GETS USED AS THE TERM
FOR NON-PROTEIN ORGANIC MOLECULES, ALL RIGHT?
SO THE CONVENTION THAT WE'LL USE IS WHEN WE'RE REFERRING
TO A METAL ION, WE'LL DESCRIBE IT AS THE COFACTOR.
AND WE'RE LOOKING AT AN ORGANIC MOLECULE,
WE'LL CALL IT THE COENZYME.
SO AN AN EXAMPLE, ZINC, RIGHT?
WE TALKED ABOUT ZINC IS IMPORTANT FOR OUR IMMUNITY
AND HEALTH.
AND IT'S AN IMPORTANT COFACTOR IN SEVERAL ENZYMES.
AND SO HERE IS ONE EXAMPLE HERE, CARBOXYPEPTIDASE IS AN ENZYME
THAT REQUIRES THE ZINC ION AS A COFACTOR.
THIS ENZYME HYDROLYZES THE FIRST AMIDE BOND
AT THE C-TERMINAL END OF PEPTIDES.
AND IT'S SECRETED OR IT'S SYNTHESIZED
IN THE PANCREAS, AND WE USE IT IN OUR SMALL INTESTINE.
AND SO THE MAIN THING HERE-- IS HERE IS THE ZINC, RIGHT?
SO THE ZINC IS THE COFACTOR.
AND SO THIS LOOKS VERY CONFUSING AND MESSY.
AND THEN IF WE LOOK HERE, SCIENTISTS HAVE COME IN
AND WE'VE INVESTIGATED AND WE'VE LEARNED MORE
ABOUT THE STRUCTURE.
AND THEN WE CAN SEE THOSE CARBOXY GROUPS, RIGHT?
WE TALKED ABOUT THE C-TERMINUS HERE.
AND WE CAN SEE HOW THE C- TERMINUS WILL HAVE THE ANIONS,
AND THAT WILL BE ELECTROSTATICALLY ATTRACTED
TO THE POSITIVE CHARGE OF THE ZINC.
SO WE CAN SEE HOW THE METALS, THROUGH THEIR ELECTROSTATIC
INTERACTIONS, CAN HELP TO SECURE A SUBSTRATE
TO THE ACTIVE SITE OF AN ENZYME, ALL RIGHT?
WITH THE COFACTORS HERE, RIGHT?
WE THINK ABOUT IT AS AN ELECTROSTATIC INTERACTION,
TO ATTRACT SUBSTRATES TO ACTIVE SITES.
SO THAT'S REALLY--THERE'S NOT A LOT TO KNOW
BUT IT'S WORTH--IT'S IMPORTANT.
SO IT'S WORTH TAKING SOME TIME TO TALK ABOUT IT.
AND NOW, WE'LL LOOK A LITTLE MORE CLOSELY AT THE COENZYMES,
THE NON-PROTEIN ORGANIC MOLECULES
THAT AN ENZYME MAY NEED TO CATALYZE REACTIONS.
SO NAD+/NADH IS A VERY IMPORTANT COENZYME PAIR.
AND WE SEE THEM A LOT.
SO HERE'S LACTATE USING LACTATE DEHYDROGENASE TO PYRUVATE.
AND SO IF WE LOOK HERE, WE LOOK THERE FOR A CHANGE,
AND WE SEE THAT THERE'S A CHANGE IN THIS PORTION
OF THE MOLECULE.
WE SEE THAT OUR SECONDARY ALCOHOL IS BEING OXIDIZED,
TO A KETONE.
AND WE LOOK A LITTLE MORE CLOSELY,
AND THEN WE LOOK AT OUR COENZYME.
AND WE SEE THAT IT IS GAINING HYDROGEN, RIGHT?
SO IT'S BEING REDUCED. OKAY.
SO WHICH SPECIES HAS BEEN REDUCED?
THAT WOULD BE THE NAD+.
AND WHICH SPECIES HAS BEEN OXIDIZED?
THAT WOULD BE THE LACTIC ACID.
NOW, IT'S IMPORTANT WHEN WE'RE LOOKING
AT BIOCHEMICAL REACTIONS TO REMEMBER THAT THE ENZYMES
CATALYZE BOTH THE FORWARD AND THE REVERSE PROCESSES.
SO SOMETIMES, YOU WANT TO LOOK AT A REACTION BACKWARDS.
SO IF WE LOOK RIGHT HERE, WE LOOK FOR THE CHANGE, RIGHT?
AND SO NOW WE'RE GOING INTO REVERSE, RIGHT?
SO WE HAVE THE REVERSE REACTION OF ABOVE.
WE SEE THE PYRUVATE THERE. AND THE KETONE OF THE PYRUVATE,
IS NOW BEING REDUCED.
SO THE KETONE IS BEING REDUCED TO AN ALCOHOL.
AND SO CONVERSELY THEN, WE LOOK AT OUR COENZYME,
WHAT'S HAPPENING TO OUR COENZYME?
OUR COENZYME IS UNDERGOING OXIDATION.
SO THE MAIN POINT HERE WAS TO JUST KEEP OUR MINDS OPEN
THAT THE REACTIONS CAN HAPPEN BOTH FORWARDS OR BACKWARDS,
DEPENDING ON WHAT'S GOING ON WITHIN OUR BODY
AND WHAT THE NEEDS ARE.
AND SO THE COENZYMES ARE THERE, IN WHICHEVER FORM
IS NEEDED TO SUPPORT THE OXIDATION-REDUCTION REACTION.
SO THAT WRAPS UP THIS BRIEF OVERVIEW
OF COENZYMES AND COFACTORS.
REMEMBERING THAT THE COFACTOR TERM WE'LL USE FOR THE METALS,
AND THE COENZYME WE'LL USE FOR THE ORGANIC MOLECULES
THAT ARE NOT PROTEINS.
PLEASE TAKE SOME TIME NOW TO WORK A FEW HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.