A critical analysis of kinetic data of 3‐hexulosephosphate synthases MICHAELIS‐MENTEN or complex characteristics

Abstract

Investigations of the 3-hexulosephosphate synthase (HPS) from different methylotrophic bacteria have revealed apparent discrepancies in kinetic behaviour. I n all methanol-utilizing species investigated by us the kinetic characteristics showed intermediary plateau regions. Therefore, this behaviour is assumed to be a general feature of the HPS from all non-methane-utilizing methylotrophic bacteria. However, this assumption is in contrast to the results of other authors. To check the validity of our assumption we have analyzed the kinetic data given by others. Indications of the existence of intermediary plateau regions could be found with the enzyme from Arthrobacter globiformis (BYKOVSKAYA and VORONKOV 1977) and Methylomonas aminoiaciens 77a (KATO et al. 1978). Furthermore, biphasic ARRHENIUS plots indicate a multiple character of the HPS from these species as could already be demonstrated with the enzyme from Bacterium MB 58 and Pseudomonas oleovorana. I n addition, causes which may obscure the detection of intermediary plateau regions are demonstrated.Our comparative investigations have shown that the kinetic characteristics of the 3-hexulosephosphate synthase (HPS) from obligate (Pseudomonas W 6 , Methylomonas methylovora) and facultative (Bacterium MB 58, P . oleovorans) methanol-utilizing bacteria exhibit intermediary plat,eau regions MULLER 1977, 1978). I n contrast to this the enzyme from the methane-utilizing "Methylomonas" GB 3 (BABEL and MULLER 1977) and "MethyZomonas" GB 8 (MULLER 1979) show MICHAELIS-MENTEN dependence.We have attributed a regulatory significance to the appearence of these intermediary plateau regions in analogy to other enzymes with such behaviour (TEIPEL and KOSHLAND 1969, KURGANOV 1975, KURGANOV et al. 1976). These plateaus were assumed to be a general feature of the HPS from methanol-(and methylamine-) utilizing bacteria. The differences to the methane-utilizing species have been attributed to the specificity of the substrates utilized (BABEL and MULLER 1977). Both for Bacterium MB58 (MULLER 1978, MULLER and BABEL, in preparation) and P . oleoworans (MULLER and SOKOLOV 1979) multiple and interconvertible forms of the HPS exhibiting a different response to substrate eaturation have been found to generate the intermediary plateau regions. A conception about the regulation of HPS in methylotrophic metabolism is given elsewhere (MULLER 1979, M~L L E R and BABEL, in preparation).However, there are apparent discrepancies between our results and the conclusions derived therefrom and the results obtained by other investigators. Both for the methanol-utilizing Methylomo~as M 15 (SAHM et al. 1976) and Meth~lomona~ arninofuciens (KATO et ul. 1977(KATO et ul. , 1978 these authors have claimed MICHAELIS-MENTEN kinetics and, thus, in general coincidence with the behaviour of the HPS from the methane-utilizing MethyZococcus capsulatus (FERENCI et al. 1974).