useful for enzymes with a known protein sequence. It is also possible to search speciﬁcally to membrane proteins using the program TMHMM (4). CONTENTS OF BRENDA BRENDA contains functional data for all enzyme classes ( 4800 entries in six main classes in 2008) that have been classiﬁed according to the EC scheme of the IUBMB [International Union of Biochemistry and Molecular Biology, (5)] irrespectively of the enzyme’s source. The range of data in BRENDA is not restricted to spe- ciﬁc aspects but includes a wide area of biochemical and molecular properties of enzymes such as Classiﬁcation and nomenclature Reaction and speciﬁcity Functional parameters Organism-related information Enzyme structure Isolation and preparation Literature references Application and engineering Enzyme–disease relationships All data and information are manually extracted from the primary literature and are connected to the biological source of the enzyme, i.e. the organism, the tissue, the subcellular localization and/or the protein sequence (if available). Since 2007, the amount of manually annotated data has increased by 18%. An overview on the data in the various sections is displayed in Table 1. NEW DEVELOPMENTS AND NEW DATA FIELDS Since the last publication (3) major developments and improvements have been included. The annotation speed has been increased and thus each EC class is updated with manually curated data every 2–2.5 years (compared with 4–4.5 years since 2006). A newly integrated search option oﬀers direct access to protein-speciﬁc data. A new numer- ical data ﬁeld (IC50, see below) has been added. Table 1. Data entries in BRENDA Enzyme information Names and synonyms Isolation and preparation Stability Reaction and speciﬁcity Enzyme structure (including sequences) Functional and kinetic parameters Organism-related information References Enzyme application Mutant enzymes IC50 (NEW) Single dataa 102 540 68 126 38 196 475 510 716 397 253 795 106 218 113 626 7718 31 421 8473 Nucleic Acids Research, 2009, Vol. 37, Database issue D589 Protein-specific search In order to search for enzyme properties speciﬁc to a cer- tain gene product and for the discrimination of diﬀerent isoforms of enzymes a new option, the protein-speciﬁc search, was introduced to the BRENDA database. The new feature is based on the UniProtKB/Swiss-Prot acces- sion codes (6). Diﬀerent isoforms can be selected directly by applying the UniProtKB/Swiss-Prot accession code or by using the search mask of the BRENDA database with recommended name, EC number or organism of the pro- tein as keywords. Thus, speciﬁc information can be obtained for each isoform of the enzyme in question. Currently, BRENDA contains diﬀerent isoforms for more than 3300 enzymes in nearly 500 diﬀerent organisms. As an example Figure 1 shows the numbers of diﬀerent isoforms of human protein kinases as a diagram. IC50 value The IC50 value is a measure of the inhibitory strength of a compound with respect to an enzyme and represents the concentration of a drug that is required for a 50% inhibi- tion in vitro. These values are commonly used for the comparison of antagonist drug potency in pharmacologi- cal research. BRENDA now stores IC50 values for inhibi- tors in the relationship inhibitor-enzyme-organism (protein sequence if available). The chemical structures of the inhibitors can be displayed or downloaded in the molﬁle format. FRENDA/AMENDA SUPPLEMENTS While the manually curated BRENDA database aims at keeping up with the newly published literature references, it is, of course, impossible to extract all relevant informa- tion for well-investigated enzyme classes. In these cases BRENDA tries to be comprehensive but cannot be complete. Therefore, since release 2006 FRENDA and AMENDA are provided as additional resources. They represent a aThe numbers refer to the combination of enzyme-organism-(protein-) value. Figure 1. Depicted are the numbers of diﬀerent isoforms for human protein kinases in BRENDA.