The inducing potential of formaldehyde on the synthesis of hexulose phosphate synthase, a key enzyme of the RuMP cycle in Arthrobacter PI, was investigated in resting cell suspensions. Induction of this enzyme only occurred at formaldehyde concentrations of 0.5 mM and below. No evidence was obtained for the involvement of an inactivation-activation mechanism that controlled the activity of existing hexulose phosphate synthase molecules.
Addition of formaldehyde at a rate of 1 mmol 9 1-1. h-1 to cells of Arthrobacter P1 growing in batch culture on the "heterotrophic" substrates glucose or acetate resulted in the immediate and very rapid synthesis of hexulose phosphate synthase. These results, obtained under carbon excess conditions, clearly show that induction by formaldehyde is the overriding control mechanism in the regulation of the synthesis of this enzyme in Arthrobacter PI. The regulation of the synthesis of this key enzyme of the RuMP cycle of formaldehyde fixation in Arthrobaeter P1 (induction by formaldehyde) is therefore completely different from that generally observed for the enzymes of the RuBP cycle of CO2 fixation in facultatively autotrophic bacteria (repression/ derepression mechanism).
Addition of methylamine at a rate of i mmol 9 1-1 -h-1 to batch cultures growing on "heterotrophic" substrates resulted in accumulation of the C~ substrate, but not in repression of the synthesis of amine oxidase. The slow start of methylamine utilization in cells growing on glucose suggests that methylamine either is a relatively weak inducer or, because in the absence of the methylamine transport system in non-induced cells, a sufficiently high intracellular level of methylamine is only slowly built up.