TABLE 3.

Substrate specificity of purified PHB depolymerase PhaZ1

SubstrateActivitya
Without pretreatmentWith pretreatment
ApdATrypsin/ovomucoid
nPHA granules isolated from:
    R. eutropha H16660b2,800b3,100b
    E. coli (phaCAB + phaP)104b560b1,600b
    E. coli (phaCAB)95b490b,d1,900b
    B. megaterium+++
    B. cereus+++
nPHV granules from C. violaceum+++
nPHO granules from P. oleovorans with or without 1 % (wt/vol) SDS<0.01b<0.01b<0.01b
Atactic PHB [poly(R-, S-3-HB)]<0.01b<0.01b<0.01b
dPHA (isotactic, paracrystalline): PHB, PHV, PHO, P(3HO-3HD)<0.01b<0.01b<0.01b
Artificial (amorphous) PHA
    PHB coated with SDS or sodium cholate++ (Cholate)++ (Cholate)+ (Cholate)
+ (SDS)+ (SDS)+ (SDS)
    PHV coated with SDS or sodium cholate+ (Cholate)+ (Cholate)+ (Cholate)
+ (SDS)+ (SDS)+ (SDS)
    PHO-latex; P(HO-co-HD)-latex<0.01b
    PHB, PHV coated with CTAB<1b<5b<1b
Other hydrolase substrates:
    Poly(6-hydroxyhexanoate)<0.01b<0.01b
    Triolein, tributyrin, olive oil<0.01b<0.01b
    Casein; N-α-benzoyl-l-arginine-4-nitranilide
    Cutin (cucumber)b (80-h incubation time)<0.01b<0.01b<0.01b
    p-Nitrophenyl estersc<0.01c<0.01c
  • a Values are units per milligram. Unless otherwise noted, turbidimetric assays were performed; 1 U mg−1 = 1 μg of polymer min−1 mg−1 Symbols:-, <1 U/mg; +, >5 U/mg; ++, >100 U/mg.

  • b Titration was performed; 1 U mg−1 = 1 μmol of acid min−1 mg−1.

  • c Turbidimetric assays (with and without detergents) were performed; values are micromoles per minute per milligram. p-Nitrophenyl ester substrates are as follows: p- nitrophenyl acetate, p-nitrophenyl butyrate, p-nitrophenyl hexanoate (p-nitrophenyl caproate), p-nitrophenyl octanoate (p-nitrophenyl caprylate), p-nitrophenyl decanoate, p- nitrophenyl hexadecanoate (p-nitrophenyl palmitate).

  • d A lag phase was observed (18).