How many enzymes are in the human body?
The Human Protein Atlas lists 3,777 human enzyme genes. UniProt release 2026_02 contains 3,716 reviewed human proteins with complete EC numbers, spanning 1,546 distinct activities.
Humans encode about 3,800 enzyme genes. Current reference databases list 3,777 genes in the Human Protein Atlas Enzymes class and 3,716 reviewed UniProt protein entries with at least one complete EC number.
The exact answer changes with the unit counted. Enzyme-coding genes, enzyme proteins, classified activities, and individual molecules are different quantities.
Our guide to how many proteins there are counts the entire human proteome, including structural proteins, receptors, antibodies, and enzymes. The enzyme count covers only the catalytic subset and separates enzyme-coding genes, reviewed enzyme proteins, EC activities, classes, and physical molecules.
How many enzymes are in the human body?
Humans have about 3,800 enzyme-coding genes. The Human Protein Atlas currently places 3,777 human genes in its Enzymes class, equal to 19.4% of the 19,442 protein-coding genes in GENCODE v50.[1][3]
UniProtKB release 2026_02 contains 4,613 reviewed human protein entries with an EC annotation. After retaining only entries with at least one complete, four-part Enzyme Commission number, 3,716 entries remain.[2]
The two totals are not expected to match exactly. The Human Protein Atlas groups genes using several enzyme lists, including separate kinase and peptidase sources. UniProt counts reviewed protein entries with complete EC annotations. Gene catalogues and protein databases also handle isoforms, multifunctional proteins, and incomplete annotations differently.
How many human enzyme activities are known?
Reviewed human proteins are associated with 1,546 distinct complete EC numbers. These numbers classify enzyme-catalyzed reactions or activities rather than genes, proteins, or physical molecules.[2][6]
Isoenzymes are different proteins that catalyze the same reaction, so they can share one EC number. A multifunctional protein can carry more than one EC number.[6] An EC number also says nothing about reaction speed. Enzyme turnover, usually reported as kcat, is a separate property.
A 2020 study found 3,428 human Swiss-Prot proteins with complete EC numbers in release 04_2019.[4] Applying the same four-part rule to current reviewed UniProt records gives 3,716 entries, 288 more. The database count changes as curators add evidence and revise annotations. It does not track the number of enzyme molecules in the body.
What are the seven types of enzymes?
The seven top-level enzyme classes are oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, and translocases. They are defined by the type of reaction they catalyze.[5][6]
Transferases account for the largest number of distinct complete EC activities represented in reviewed human proteins, followed by hydrolases and oxidoreductases.
ProteinIQ calculated the chart from the UniProt records used above by retaining complete four-part EC numbers, removing duplicate EC numbers, and grouping the remaining 1,546 activities by their first digit.[2] The resulting counts are 334 oxidoreductase, 524 transferase, 444 hydrolase, 91 lyase, 60 isomerase, 75 ligase, and 18 translocase activities.
Older sources often list six classes because translocases were added as EC 7 in 2018. These enzymes catalyze the movement of ions or molecules across membranes or their separation within membranes.[5]
Why do enzyme counts differ?
Enzyme genes, enzyme proteins, EC activities, and enzyme molecules are different units. The current evidence supports about 3,800 human enzyme genes, 3,716 reviewed enzyme protein entries with complete EC numbers, and 1,546 distinct complete EC activities.[1][2]
The number of physical enzyme molecules is far larger and has no fixed whole-body total. Each enzyme type can occur in many copies, and its abundance changes between tissues, cell types, developmental stages, and physiological states. The human protein count has the same measurement problem: protein types and protein molecules are different units.
The claim that the human body contains 75,000 distinct enzymes does not match curated human gene or protein inventories. It is not a count of enzyme-coding genes, reviewed enzyme proteins, or classified EC activities. For enzyme types encoded by humans, about 3,800 is the defensible answer.
