TABLE 1.

GDO activity in cell extracts^a

Strain	Growth substrate	Sp act (nmol of O2/min/mg of (protein)b
Haloferax sp. strain D1227	BA	427 ± 32
	Pyruvic acid	ND
Haloarcula sp. strain D1	BA	3.7 ± 0.1
	4-HBA	2.6 ± 0.1
	Pyruvic acid	ND

^aGDO activity in crude cell extracts was assayed by measuring the rate of gentisate-dependent oxygen uptake using a Clarke-type oxygen electrode, as described in the text.

^bThe specific activities shown are the means of duplicate assays (± standard deviation) performed in buffer containing 3 M KCl; ND, no activity was detected. No GDO activity remained in control extracts which were preincubated with 2,2′-dipyridyl (1 mM) for 15 min. No substrate-dependent oxygen uptake was measured in any extract in response to the addition of the following compounds: catechol (1,2-dihydroxybenzene); protocatechuate (3,4-dihydroxybenzoic acid); 2,3-, 2,4-, 2,6-, or 3,5-dihydroxybenzoic acid; 2,3,4- or 2,4,6-trihydroxybenzoic acid; or hydroquinone (1,4-dihydroxybenzene). Addition of either hydroxyhydroquinone (HHQ) or 3,4,5-trihydroxybenzoic acid to cell extracts resulted in detectable increases in O₂ uptake rates. However, as these compounds also induced equivalent or higher levels of O₂ uptake in buffer-only control assays (up to 60 nmol of O₂/min in the case of HHQ), this was attributed to their rapid autoxidation in the oxygen electrode cell.