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  1. Lac Repressor

    Linked via "homodimer"

    Structure and Composition
    The Lac Repressor is synthesized as a polypeptide of 360 amino acid residues. It predominantly functions as a tetramer in its fully active state, although the biologically relevant unit often observed interacting with DNA is the homodimer, formed by the association of two monomers [2]. The monomer structure is characterized by distinct functional domains:
    N-terminal DNA-Binding Domain ($\text{DBD}$): Res…

  2. Lipid Biosynthesis

    Linked via "homodimer"

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    The subsequent chain elongation is carried out by the multi-enzyme complex known as the Fatty Acid Synthase ($\text{FAS}$). In mammals, $\text{FAS}$ exists as a homodimer ($\text{FAS}$ I), whereas plants and bacteria utilize a complex of independently functioning enzymes ($\text{FAS}$ II). The iterative two-carbon addition process requires the sequential action of $\text{FAS}$ components: condensation, reduction (using NADPH), dehydration, an…

  3. Transcription Factor

    Linked via "homodimers"

    Helix-Turn-Helix ($\text{HTH}$): Found widely in prokaryotic repressors (e.g., the Lac Repressor). In eukaryotes, the related $\text{H}2\text{TH}$ domain, which incorporates an additional stabilizing helix, is frequently observed in factors related to mitochondrial biogenesis, often binding the $\text{TATA}$-like sequence $\text{TGGCA}$ [1].
    Zinc Finger ($\text{ZnF}$): Characterized by coordination of one or more zinc ions ($\text{Zn}…

  4. Transketolase

    Linked via "homodimer"

    Structure and Cofactor Requirements
    Transketolase is typically a homodimer or homotetramer, depending on the organism and ionic strength of the surrounding medium. Structurally, it possesses two distinct domains: the $\text{TPP}$-binding domain and the substrate-entry channel, which is lined with highly polarized glutamine residues that actively repel non-phosphorylated substrates, thereby ensuring strict adherence to pathway fidelity [4].
    The enzyme absolutely requ…

  5. Transketolase

    Linked via "Homodimer"

    | :--- | :--- | :--- | :--- |
    | Mammals | Homotetramer | $\text{NADPH}$ Generation, Nucleotide Precursors | Regulation by cytosolic $\text{Ca}^{2+}$ pulses |
    | Plants (C3) | Homodimer | $\text{RuBP}$ Regeneration (Calvin Cycle) | Utilizes Fructose 6-P as a competitive inhibitor at high light intensity |
    | Archaea (Methanogens) | Monomer | Sugar Interconversion un…