TABLE 2.

Thermostability of the sulfopyruvate decarboxylase

Expt	Heating conditionsa	Conditions of enzymatic assayb	Sulfoacetaldehyde produced (nmol)	% of maximum conversion
1	No heating	Argon, SP, dt, mv	208	99
2	TES buffer	Argon, SP	40	19
3	TES buffer	Argon, SP, dt, mv	38	18
4	Phosphate buffer	Argon, SP, dt, mv	206	98
5	Phosphate buffer	Argon, SP	27	13

^aCrude cell extracts containing the overproduced ComDE protein (58 μg of protein/ml) were heated in the indicated pH 7.0 buffer for 15 min at 80°C under an atmosphere of argon and then centrifuged; the clear liquid was transferred into a new septated glass vial under an atmosphere of argon (21 μg of protein/ml after the heat treatment). 

^bFor the determination of the enzymatic activities, the nonheated (5.8 μg of protein) and heat-purified cell extracts (1.1 μg of protein) were mixed with 2.1 mM sulfopyruvate (SP) for 15 min at 80°C under an atmosphere of argon. The addition of 2 mM dithionite (dt) was always accompanied by addition of 0.2 mM methylviologen (mv). The amounts of sulfopyruvate and sulfoacetaldehyde, as their DNPH derivatives, were analyzed by HPLC.