The enzymes of primary and intermediate metabolic pathways were studie
d in a psychrophilic methanotroph having an optimal growth temperature
lower than 15-degrees-C. The strain was shown to oxidize methane to C
O2 via methanol, formaldehyde, and formate by means of corresponding d
ehydrogenases. Assimilation of methane carbon occurs at the level of f
ormaldehyde via the ribulose monophosphate cycle. Ammonium nitrogen is
assimilated via the glutamate cycle and via reductive amination of py
ruvate by means of alanine dehydrogenase. Although strain Z-0021 has s
ome properties of group X of methanotrophs, it was assigned to group I
according to the set of enzymes of carbon metabolism. The activities
of all the studied enzymes of the psychrophilic methanotroph decreased
substantially as the temperature was lowered.