4-Guanidinobutyrate amidinohydrolase (EC 3.5.3.7) was purified about 360-fold to apparent homogeneity from Pseudomonas sp. ATCC 14676. The molecular weight of the enzyme was estimated to be 180, 000_??_186, 000 by gel filtration procedure and the method of Hedrick and Smith. The subunit molecular weight was estimated to be 33, 000_??_36, 000 by SDS-polyacrylamide gel electrophoresis. The enzyme was optimally active at pH 10.2 in sodium carbonate buffer. EDTA inactivated the enzyme during incubation at 50°C in phosphate buffer (pH 7.0). Incubation of the inactivated enzyme with Mn²⁺ restored full activity. The enzyme was inactivated with PCMB, and the PCMB-inactivated enzyme was reactivated by incubation with 2-mercaptoethanol. The enzyme specifically acted toward 4-guanidinobutyrate; 5-guanidinovalerate and 6-guanidinocaproate were hydrolyzed at very low rates. The Km value for 4-guanidinobutyrate was 33mM. Propionate and n-butyrate were competitive inhibitors of the enzyme with Ki values of 2.0mM and 0.5mM, respectively. These properties were compared with those of the analogous guanidinoacetate amidinohydrolase from the same organism.

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