Guanidinobutyrase for L-arginine degradation in Brevibacterium helvolum

Guanidinobutyrase (guanidinobutyrate amidinohydrolase, EC. 3.5.3.7) catalyzing the third step of the arginine oxygenase pathway in Brevibacterium helvolum IFO 12073 (ATCC 11822) was purified to homogeneity and characterized. The enzyme had a molecular weight of 190,000 and was composed of four apparently identical subunits with a molecular weight of 45,000. The E(1%) value at 280 nm of the enzyme protein was 2.4. The enzyme contained 0.5 mol of firmly bound Zn 2+ per mol of subunit. The enzyme was highly specific for 4-guanidinobutyrate, but had a weak activity toward L- and D-arginine. The Michaelis constant (K m ) for 4-guanidinobutyrate was 2.9 mM. The optimum pH was 9.0. Strong mixed type inhibition was observed with thioglycolate and several other thiol compounds. These properties were compared with those of the enzyme of fluorescent Pseudomonas and discussed.