In the Pseudomonas aeruginosa branchpoint discussed here, IDH denotes the isocitrate dehydrogenase activity insensitive to AceK phosphorylation and regulated allosterically by metabolic effectors. The abbreviation is context-dependent across organisms.

isocitrate lyase cleaves isocitrate into succinate and glyoxylate. It competes with isocitrate dehydrogenases for the branchpoint substrate and initiates the glyoxylate shunt.

malate synthase combines glyoxylate with an acetyl unit from acetyl-CoA to form malate. Together with isocitrate lyase it provides the characteristic carbon-conserving route of the glyoxylate shunt.

AceK is a bifunctional isocitrate-dehydrogenase kinase/phosphatase. Metabolic effectors regulate its competing activities; in Pseudomonas aeruginosa it controls ICD but not the separate IDH enzyme.

A family of proteolytic enzymes involved in processes including apoptosis. A caspase reporter is evidence about pathway activity and should be interpreted together with cellular morphology and subsequent fate.

An enzyme catalysing decomposition of hydrogen peroxide into water and oxygen. Compartment-specific activity can be used to test contributions of peroxide buffering.

Steroid 5α-reductase reduces the conjugated double bond of particular steroids using NADPH. Human type 2 can convert testosterone to dihydrotestosterone and generate an inhibitory enzyme cofactor adduct from finasteride.

In mechanism-based inhibition, catalytic processing of an inhibitor generates the species responsible for sustained inhibition. The covalent bond can be between inhibitor and enzyme cofactor rather than to an amino acid side chain; persistence must be described on the relevant timescale.

METTL3 is a catalytic component of a protein complex that deposits N6-methyladenosine on RNA, especially messenger RNA. It works with METTL14 and regulatory components rather than determining every cellular methylation site in isolation. Modification can affect RNA processing, stability or biological translation through proteins that recognize the mark. The effect of a METTL3 perturbation therefore depends on which transcripts and readers are present. ^[ref]

An enzyme hydrolysing beta-galactosides. In the lac operon system, its processing of lactose includes production of allolactose, which regulates LacI.

A spatially organized group of three catalytic residues. Serine proteases commonly use serine, histidine and aspartate, but similar geometry in different folds can reflect convergent evolution.

A mitochondrial enzyme converting pyruvate into oxaloacetate using bicarbonate and ATP. It supplies gluconeogenesis and replenishes metabolic intermediates; compartmentation requires suitable subsequent transport routes.

An enzyme system hydrolysing glucose-6-phosphate to glucose and phosphate. The hepatic catalytic site faces the endoplasmic-reticulum lumen, so substrate transport is integral to glucose production.

An enzyme coupling electrons from reduced ferredoxin to NADP reduction, producing NADPH on the stromal side of the chloroplast electron-transfer system.

An enzyme cleaving a phosphodiester linkage. Cyclic-nucleotide phosphodiesterases reduce cyclic AMP or cyclic GMP signals, so inhibiting them can prolong a messenger response.

An enzyme hydrolysing GTP to GDP and phosphate. Many act as nucleotide-controlled switches: hydrolysis changes the state, and nucleotide exchange restores a GTP-bound molecular population for another cycle.

Adenosine deaminase catalyzes conversion of adenosine and water into inosine and Ammonia. Its zinc-containing active site activates water and stabilizes the reacting configuration; proton transfers assist addition and leaving-group departure. Mutation kinetics constrain catalytic roles but do not uniquely locate every proton.

A peptidyl-prolyl isomerase used to study connections between conformational exchange and catalysis.^[ref]

The erythroid aminolevulinate-synthase isoform, with an iron-responsive RNA element coupling its synthesis to iron supply for the haem pathway.

An iron–sulfur enzyme. The cytosolic form associated with IRP1 illustrates switching between enzymatic and RNA-binding functions.