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How many enzymes are in the human body?
The human genome contains about 3,800 enzyme-coding genes. Learn why gene counts, enzyme proteins, EC numbers, enzyme classes, and enzyme molecules give different totals.
Matic Broz Computational chemist
Humans encode about 3,800 enzyme genes. This is the best short answer to how many enzyme types are in the human body. The number of individual enzyme molecules is much larger and changes from cell to cell.
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 about 19% of the 19,442 protein-coding genes in the current GENCODE annotation.[1][3]
An independent count from UniProt gives almost the same result. On July 23, 2026, 3,716 manually reviewed human protein entries had at least one complete, four-part Enzyme Commission number.[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 identify classified biochemical activities rather than genes or protein molecules.[2]
An EC number describes the reaction an enzyme catalyzes. More than one human protein can share the same EC number, while 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 often-repeated 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.
Sources▼
- Protein classes Human Protein Atlas · July 23, 2026. https://www.proteinatlas.org/humanproteome/proteinclasses
- Reviewed human UniProtKB entries with EC number annotations UniProt · July 23, 2026. https://rest.uniprot.org/uniprotkb/stream?query=%28organism_id%3A9606%29%20AND%20%28reviewed%3Atrue%29%20AND%20%28ec%3A%2A%29&format=tsv&fields=accession%2Cgene_primary%2Cec
- Human release statistics (v50) GENCODE · July 23, 2026. https://www.gencodegenes.org/human/stats.html
- Highlighting Human Enzymes Active in Different Metabolic Pathways and Diseases Biomedicines · 2020. https://www.mdpi.com/2227-9059/8/8/250
- Translocases (EC 7): A new EC class Nomenclature Committee of the International Union of Biochemistry and Molecular Biology · 2018. https://iubmb.qmul.ac.uk/newsletter/2018.html
- How to Name and Classify Your Enzyme Nomenclature Committee of the International Union of Biochemistry and Molecular Biology · July 23, 2026. https://iubmb.qmul.ac.uk/enzyme/advice.html
Founder and computational chemist, ProteinIQ
Dr. Matic Broz is the founder of ProteinIQ and a computational chemist. He completed a PhD focused on protein structure, molecular dynamics, and neural networks, and writes about structural biology and scientific software.