ENTRY       EC 3.4.21.42
NAME        Complement subcomponent C1s-
            C1 esterase
CLASS       Hydrolases
            Acting on peptide bonds (peptidases)
            Serine endopeptidases
REACTION    Cleavage of Arg+Ala bond in complement component C4 to form C4a
            and C4b, and Lys(or Arg)+Lys bond in complement component C2 to
            form C2a and C2b: the 'classical' pathway C3 convertase
SUBSTRATE   Complement component C4
            Complement component C2
            H2O
PRODUCT     Complement component C4a
            Complement component C4b
            Complement component C2a
            Complement component C2b
COMMENT     Activated from proenzyme C1s in plasma by complement
            subcomponent C1r-
DISEASE     MIM: 120580  Complement component-1, s subcomponent; C1r/C1s
                         deficiency, combined (1)
MOTIF       PS: PS00134  [LIVM]-[ST]-A-[STAG]-H-C
            PS: PS00135  [DNSTAGC]-[GSTAPIMVQH]-x(2)-G-[DE]-S-G-[GS]-[SAPHV]-
                         [LIVMFYWH]-[LIVMFYSTANQH]
GENES       HSA: C1S(Hs.1280)
DBLINKS     University of Geneva ENZYME DATA BANK: 3.4.21.42
            WIT (What Is There) Metabolic Reconstruction: 3.4.21.42
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