KEGG Identifier

KEGG Data Objects and Identifiers

KEGG data objects are biological entities from molecular to higher levels that are used to represent the KEGG model (see overview). Currently, there are 23 types of KEGG data objects, including pathways, genes and protein, small molecules, reactions, diseases and drugs. The KEGG data object identifer or simply the KEGG identifier (kid) is a unique identifier for each KEGG data object.

KEGG Identifier

The KEGG identifier is a unique identifier in the entire KEGG. Generally, it takes the form of a prefix followed by a five-digit number as shown below:

Data object		Content	Prefix		WebLinks example
pathway		KEGG pathway maps	map	<org> ko, ec, rn	map00010 hsa04930	map00010 hsa04930
brite		BRITE hierarchies and tables	br, jp ko	<org>	br:08303 br:01002	br08303 ko01002
module		KEGG modules	M	<org>_M	M00010	M00010
ko		KO functional orthologs	K		K04527
genes	<org> ag vg vp	Genes in KEGG organisms Addendum proteins Viral genes Viral mature peptides	- - - -		hsa:3643 ag:CAA76703 vg:155971 vp:155971-1
genome vtax vgenome		KEGG organisms KEGG viruses Viral pathogens	T[01] - T4		T01001 (gn:hsa) gn:2697049 T40361
compound		Metabolites and chemical substances	C		C00031
glycan		Glycans	G		G00109
reaction rclass rmodule		Biochemical reactions Reaction class Reaction modules	R RC RM		R00259 RC00046 RM00601 RM006
enzyme		Enzyme nomenclature	-		ec:2.7.10.1
network ntmap variant		Disease-related network elements Network variation maps Human gene variants	N nt -		N00002 nt06210 nt06210 hsa_var:25v1
disease		Human diseases	H		H00004
drug dgroup		Drugs Drug groups	D DG		D01441 DG00710

<org> represents three- or four-letter organism code

Exceptions are GENES identifiers (including variant identifiers), Vtax identifiers for viruses and EC numbers for enzymes, which follow the general form of the the DBGET retrieval system (see About DBGET). Each entry in DBGET is identified by

<database>:<entry>

where <database> is the database name and <entry> is the entry name or the accession number (see DBGET for the list of database names and abbreviations).

The KEGG identifiers without prefixes are often called D numbers, K numbers, C numbers, etc. Since these numbers are unique across the entire KEGG, <database> may be omitted in the DBGET system. For example,

D01441
dr:D01441
drug:D01441

are all equivalent.

KEGG Organism Code

In addition to the T number shown above, an organism in KEGG is given a three- or four-letter KEGG organism code, which is treated like a database name. Therefore, individual genes in an organism can be identified in the following way:

<org>:<gene>

where <org> is the KEGG organism code and <gene> is the KEGG GENES entry name taken from GeneID or Locus_tag of RefSeq or GenBank (see GENES). The KEGG organism code is also used as a prefix to identify organism-specific pathway maps or BRITE functional hierarchies.

Vtax Identifier

The virus gene (vg) category of the GENES database is generated from the NCBI RefSeq dataset. The virus genomes are distinguished by the NCBI taxonomy ID (which may change ocassionally), called Vtax identifier. Vtax entries are part of the GENOME database.

KEGG DB Links

KEGG data objects are tightly integrated by mutual links within KEGG, and are also linked to related entries in outside databases. The following table shows the links maintained by KEGG. There are additional links maintained by GenomeNet (see LinkDB), including those created by outside databases.

Data object	Internal links	Outside links
Data object	Internal links	ID conversion¹	Other
pathway	module ko <org> genome compound glycan reaction rclass rmodule enzyme network disease drug pubmed		go umbbd
brite	module ko <org> genome compound glycan reaction disease drug		go
module	pathway brite ko <org> genome compound glycan reaction rmodule enzyme pubmed
ko	pathway brite module genes <org> vg vp ag reaction rclass enzyme network disease drug pubmed		cog go tc cazy
<org>	pathway brite module ko genome enzyme (network disease drug)²	ncbi-geneid ncbi-proteinid uniprot	pfam <original_dbs>³
vg	ko genome enzyme	ncbi-geneid ncbi-proteinid uniprot	pfam taxonomy refseq
vp	ko enzyme	ncbi-proteinid	genbank
ag	ko genome enzyme pubmed	ncbi-proteinid uniprot	pfam taxonomy genbank
genome	pathway brite module <org> compound disease pubmed taxonomy		assembly genbank refseq
vtax	brite vg vp vgenome taxonomy		refseq
vgenome	brite vtax disease pubmed taxonomy		refseq
compound	pathway brite module genome glycan reaction enzyme network disease drug	pubchem chebi	cas lipidmaps lipidbank knapsack pdb-ccd 3dmet j-global
glycan	pathway brite module compound reaction enzyme	pubchem chebi	ccsd glytoucan jcggdb lipidbank glycoepitope
reaction	pathway brite module ko compound glycan rclass enzyme		rhea
rclass	pathway ko reaction enzyme
rmodule	pathway module
enzyme	pathway module ko <org> vg vp ag compound glycan reaction rclass		explorenz iubmb expasy umbbd brenda cas
network	pathway ko hsa compound variant pubmed
ntmap	pathway module ko hsa compound variant disease drug
variant (hsa_var)	network disease drug pubmed		clinvar dbsnp dbvar cosmic omim
disease	pathway brite ko hsa genome network drug pubmed		icd-11 icd-10 mesh omim medlineplus
drug	pathway brite ko hsa compound variant disease dgroup atc jtc ndc yk	pubchem chebi	cas pdb-ccd ligandbox j-global
dgroup	drug atc

¹ Outside links for ID conversion allow, for example, outside identifiers to be used in KEGG Mapper analysis. The Conv ID tool in KEGG Mapper may be used to convert GeneIDs, ProteinIDs or UniProt IDs to KEGG identifiers.
² Parentheses for hsa (Homo sapiens) only.
³ <original_dbs> include: mirbase ensembl cyorf cyanobase nite rhizobase genedb pasteur flybase vega vectorbase ... (total of >70 dbs)

Last updated: June 17, 2026