An enzyme that removes particular histone methyl marks.

Different demethylases act on different residues and methylation states, so removal of H3K4 methylation and removal of H3K27 trimethylation are distinct activities. Regulated removal makes a chromatin mark reversible without requiring replacement of the underlying DNA sequence. ^[ref]

An enzyme attaching an appropriate amino acid to a cognate transfer RNA. Reduced charging can slow decoding even if ribosome initiation remains active.

An Escherichia coli enzyme activated on starved ribosomes that produces (p)ppGpp.^[ref]

Ornithine decarboxylase converts ornithine to putrescine with release of carbon dioxide, beginning a major route of polyamine biosynthesis. Its regulation includes binding to antizyme, which can inhibit activity and promote protein degradation. This gives a compact example of controlling a metabolic pathway by changing both catalytic availability and enzyme lifetime. ^[ref]

An enzyme that changes DNA topology through controlled strand breakage and rejoining, helping resolve supercoiling and molecular interlinking.

A topoisomerase that transiently breaks both strands of one DNA duplex to permit another segment to pass, contributing to resolution of replicated chromosome interlinks.

Flap endonuclease 1, involved in processing displaced DNA structures during eukaryotic lagging-strand maturation and other DNA transactions.

A reverse-transcriptase-containing enzyme that extends telomeric DNA using an associated RNA template, contributing to chromosome-end maintenance in many eukaryotes.

An enzyme that separates DNA strands using chemical energy, enabling replication and other DNA transactions.

A histone acetyltransferase catalyses acetyl-group transfer to histone residues. The resulting changes in charge and reader-protein recruitment can influence chromatin accessibility; the effect depends on the modified site and regulatory context.

Subtilisin E is a protease used as a model in protein-engineering experiments. Sequential mutagenesis and screening for activity in organic solvent illustrate optimization without requiring a complete predictive model of every substitution.

A Kemp eliminase is a catalyst for Kemp elimination. Computationally designed protein examples allow tests of active-site construction and subsequent optimization by directed evolution.

Protein phosphatase 1 catalyses protein dephosphorylation in regulated complexes. Association with targeting partners matters: effects on one substrate do not imply indiscriminate dephosphorylation of all cellular proteins.

Glycogen synthase extends glycogen using activated glucose donors. Its activity is regulated by phosphorylation and metabolites, and its activation can be coordinated with inactivation of glycogen phosphorylase.

Creatine kinase catalyses reversible transfer between phosphocreatine and ADP to yield creatine and ATP. Inferring free ADP from this reaction requires an appropriate equilibrium model and information about pH, magnesium and the creatine pool.

Violaxanthin de-epoxidase catalyses steps of conversion from violaxanthin towards zeaxanthin under suitable thylakoid-lumen conditions. Its activity links lumen acidification to a change in antenna pigment composition.

STN7 kinase is required for plant LHCII phosphorylation associated with state transitions. Mutant and complementation experiments can separate its regulatory role from general loss of photosynthetic competence.

An enzyme that adds adenosine residues to an RNA $3^{\prime }$ end using ATP. Supplying a correctly pre-cleaved substrate separates the extension reaction from the preceding cleavage step.

A covalent enzyme intermediate bearing an acyl group during catalysis. Its formation and breakdown can occur at different rates, producing burst kinetics if the first released reaction product reports a fast step.

An enzyme interconverting ATP, ADP and AMP through $2\mathrm{ADP}\rightleftharpoons \mathrm{ATP}+\mathrm{AMP}$. Near equilibrium, AMP:ATP is proportional to the square of ADP:ATP under fixed conditions.