Alternative carboxylation reactions in type II methylotrophs and the localization of carboxylase activities in the intra-cytoplasmic membranes.

The peripheral arrangements of the intra-cytoplasmic membranes (ICM) as well as the guanine + cytosine (G + C) content of 63% indicate that our obligate methanotrophic strain M 102 would belong to the type II Methylotrophs. There are no active transport mechanisms for some organic additives, some of which are known to stimulate CO2-fixation. The CO2-acceptor molecules, Pyr (pyruvate) and PEP (phospho-enolpyruvate), must be metabolically intracellularly furnished. More than one carboxylating system could be induced in cell fractions. The carboxylating activities were variably registered in cell-free extracts and fragments. Indications that the site of the carboxylating activities are the ICM are discussed. The fact that the CO2-fixation intensities decreased at about the middle of the active growing phase indicates that the formation of the intermediate C4-compound OAA (oxaloacetate) must be furnished through some reactions by-passing the PEP-carboxylation step. The common serine-pathway for C1-assimilation is rearranged so as to fit in the discussed findings.