Lactate dehydrogenase is one of the many enzymes that...

Name: Problem 17, Chapter 13: Principles of Biochemistry
Uploaded: 2021-02-12T21:06:35-08:00
Duration: 3 min 47 s
Channel: Niamat Khuda
Description: Lactate dehydrogenase is one of the many enzymes that require NADH as coenzyme. It catalyzes the conversion of pyruvate to lactate: (FIGURE CAN'T COPY) Draw the mechanism of this reaction (show electron-pushing arrows). (Hint: This is a common reaction throughout metabolism; the mechanism is similar to that catalyzed by other dehydrogenases that use NADH, such as alcohol dehydrogenase.)

Lactate dehydrogenase is one of the many enzymes that require NADH as coenzyme. It catalyzes the conversion of pyruvate to lactate: (FIGURE CAN'T COPY) Draw the mechanism of this reaction (show electron-pushing arrows). (Hint: This is a common reaction throughout metabolism; the mechanism is similar to that catalyzed by other dehydrogenases that use NADH, such as alcohol dehydrogenase.)

Lactate dehydrogenase is one of the many enzymes that require NADH as coenzyme. It catalyzes the conversion of pyruvate to lactate: (FIGURE CAN'T COPY)
Draw the mechanism of this reaction (show electron-pushing arrows). (Hint: This is a common reaction throughout metabolism; the mechanism is similar to that catalyzed by other dehydrogenases that use NADH, such as alcohol dehydrogenase.)

Key Concepts

Electron-Pushing Arrows in Mechanism Drawing

Electron-pushing arrows are a fundamental tool in organic chemistry, used to represent the movement of electrons during chemical reactions. They visually depict the stepwise process of bond formation and breakage, helping to illustrate the detailed sequence of electron transfers, such as hydride transfer, in a reaction mechanism. This graphical method is invaluable for understanding and communicating the mechanisms of enzyme-catalyzed redox reactions.

Oxidoreductase Enzymes

Oxidoreductases are a class of enzymes that catalyze oxidation-reduction reactions. These enzymes work by facilitating the transfer of electrons from one molecule (the reductant) to another (the oxidant). In the case of lactate dehydrogenase and similar enzymes, the oxidation of NADH is coupled with the reduction of a substrate, a process that is critical for cellular metabolism and energy production.

Enzyme Active Site Catalysis

Enzyme active sites provide a highly specialized microenvironment that enhances reaction rates and specificity. In redox reactions, the active site not only binds the coenzyme (such as NADH) and the substrate but also often includes amino acid residues that act as acid or base catalysts. These residues facilitate proton transfers and stabilize transition states, ensuring that the hydride transfer and overall reaction proceed efficiently and with high specificity.

NADH as a Cofactor

NADH is a key coenzyme involved in redox reactions where it serves as an electron and hydride donor. In many enzymatic reactions, it provides the reducing power necessary to convert substrates from an oxidized to a reduced state. In the context of dehydrogenase enzymes, NADH donates a hydride ion (H?) to the substrate, facilitating the formation of a new chemical bond and altering the oxidation state of the substrate.

Hydride Transfer Mechanism

The hydride transfer mechanism is central to reactions catalyzed by dehydrogenase enzymes. In this process, a hydride ion is directly transferred from NADH to the electrophilic carbonyl carbon of the substrate. This transfer not only reduces the carbonyl group to an alcohol group but also converts NADH back to its oxidized form, NAD?, which can then be recycled in metabolic pathways.

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