The binding of bongkrekate to mitochondria

The binding of bongkrekate to mitochondrial membrane was investigated using [3H]bongkrekate. These measurements were designed to examine the previously derived reorienting site mechanism which implies that bongkrekate binds to the single carrier site only from the inner face of the mitochondrial membrane. The binding studies confirm pH-dependent accumulation of [3H]bongkrekate inside the mitochondria which superimposes on to binding of carrier sites. By breaking the membrane with Lubrol or sonication, binding to the carrier sites can be titrated and Kd approximately equal to 5 X 10(-8) M is determined. ADP or ATP increases the amount of binding but does not change the Kd. Reciprocally bongkrekate increases ADP binding in those sections of a titration curve where bongkrekate binding is increased by ADP. [35S]Atractylate is displaced by [3H]bongkrekate at a 1:1 molar ratio. This displacement is dependent on ADP concentration with the Km = 0.5 X 10(-6) M. The earlier described isomer, isobongkrekate, also binds specifically to the carrier sites. From competition with bongkrekate a ratio KisoBKAd/KBKAd = 0.10 is determined. [35S]Carboxyatractylate displaces most of [3H]isobongkrekate but only little of [3H]bongkrekate. The rate of displacement is more than 10-times faster for isobongkrekate than for bongkrekate. The displacement is dependent on ADP with a Km = 5 X 10(-6) M. All these results are fully consistent with the single site reorienting mechanism. In no instant do bongkrekate and atractylate as well as ADP or ATP bind simultaneously to the carrier.

[Regulation of citrate synthase in facultative methylotrophic bacteria]

Commonly the TCA cycle fulfils an anabolic and a catabolic function in case of aerobic chemoorganoheterotrophic nutrition. In methylotrophic growth the TCA cycle is dispensable as a bioenergetic pathway. This is reflected by properties of citrate synthase in facultative methylotrophic bacteria. Two citrate synthases, a "chemoorganoheterotrophic" one, which is inhibited by NADH (or ATP in Acetobacter MB 58), and a "methylotrophic" one, which is not or less affected by energy indicators, were found in Pseudomonas oleovorans, Pseudomonas MS, Pseudomonas MA, and Acetobacter MB 58. The concentration of these citrate synthases depends on the manner of nutrition. Bacteria with ICL-negative-variant of the serine pathway and with ribulosebisphosphate pathway seem to possess only a "chemoorganoheterotrophic" citrate synthase. Possibly the anabolic function of this citrate synthase can be realized by metabolites.

[Improvement of Y-values of Hansenula polymorpha growth on methanol by simultaneous utilization of glucose]

The simultaneous utilization of methanol and glucose by Hansenula polymorpha MH20 was investigated in chemostat (C-limited) cultivation. The mixed-substrate utilization results in biomass yields which are greater up to 20 to 25% as expected assuming an additive growth on both substrates. This is referred to as an auxiliary-substrate effect. Additionally, methanol can be utilized at higher growth rates in the presence of glucose compared to those obtained on this substrate alone. The extend of the auxiliary-substrate effect and the optimum ratio of substrates to reach this effect depend on dilution rate. The greatest stimulation in yield is obtained at D approximately 0.1 h-1, after raising the dilution rate this effect diminishes. At a rate of 0.1 h-1 the optimum mixed-substrate ratio of methanol: glucose is 7:1 (g). By increasing the growth rate the ratio changes toward glucose and reached a value of 1:1 (g) at D = 0.3 h-1. This change in the optimum ratio correlates with diminution in yield coefficient of methanol accompanying an increase in growth rate greater than 0.15 h-1. Energy balances of the utilization of the single substrates are used for interpretation of these results. From this it is evident that methanol does not play the role of an energy-rich substrate in the metabolism of yeast. Rather glucose is the energy-providing substrate in this combination.

[Cytochrome pattern of methylotropic acetic acid bacterium MB 58 as dependent on growth conditions]

In contrast to methylotrophic bacteria investigated up to now the facultative methylotrophic Bacterium MB 58 (Acetobactersp. MB 58) does not possess a cytochrome aa3-complex, but we could find out cytochrome, cytochrome cco, cytochrome a1, and moreover cytochrome d in dependence on the growth conditions. Cytochrome d was found only in stationary phase of heterotrophic growth. Under methylotrophic growth conditions cytochrome d could be demonstrated only by lowering of the aeration rate during the fermentation, by variation the pH-value of the growth medium from 4.0 to 6.5 and with low growth rates (low dilution rates) during continuous fermentation. The addition of cyanide to the oxidized suspension of bacteria during the registration of the cytochrome-redox-difference spectrum allowed the selective representation of cytochrome d under all conditions even if no identification was possible in the spectrum normally. The oxidation of cytochrome d of Acetobacter sp. MB 58 in the presence of cyanide is an indication of its cyanide insensitivity. The low level of b-type cytochromes could be represented by a special technique for registration of spectra. In this connection a unknown absorption peak at 570 nm was registered. The cyanide insensitivity of cytochrome d from Acetobacter sp. MB 58 and the occurrence of several terminal oxidases is appreciated as a hint for a branched respiratory chain.

[Regulation of PEP-carboxylase of the facultative methylotrop Acetobacter sp. MB 58]

Acetobacter sp. MB 58 assimilates methanol via the fructose-1,6-bisphosphate variant of the hexulose phosphate pathway. Glyceraldehyde-3-phosphate originates as net product of an assimilation loop involving the regeneration of the C1-acceptor ribulose-5-phosphate and must be available for the de novo synthesis of the C1-acceptor as well as for the oxidative glycolysis. It is made probable in a regulatory model that this is accomplished via alternating anabolic and catabolic phases which are controlled by concerted action of PEP-carboxylase and pyruvate kinase. Whereas Ac-CoA is a crucial effector and alpha-ketoglutarate and aspartate are inhibitors for the PEP-carboxylase, the pyruvate kinase is assumed to be regulated by energy charge.

Amino acid sequence determination of the ADP,ATP carrier from beef heart mitochondria. The sequence of the C-terminal acidolytic fragment

The primary structure of the C-terminal region (94 residues) of the ADP,ATP carrier of beef heart mitochondria is described. CNBr cleavage results in a large peptide (CB1) with Mr 22 000 and several small peptides (CB2 to CB8). Peptide separation was achieved by gel chromatography with 80% formic acid or with an ethanol/formic acid mixture. The amino acid sequence of the small CNBr peptides was determined by solid-phase techniques. Hydrolysis in formic acid cleaves the carrier protein into an Mr 23 000 fragment (A1) with the blocked N-terminus and an Mr 10 000 fragment (A2) starting with proline. The alignment of two CNBr fragments was possible by degradation of A2 by solid-phase methods for 34 steps. The remaining CNBr fragments were arranged by sequencing the tryptic peptides of citraconylated A2.

Dihydroxyacetone kinase of methanol-assimilating yeasts. II. Partial purification and some properties of dihydroxyacetone kinase from Candida methylica

Dihydroxyacetone kinase (DHAK) from the cell-free extract of methanol-grown Candida methylica was partially purified about 100-fold by a procedure employing streptomycin sulfate fractionation, ammonium sulfate fractionation, negative absorption on Cibacron blue F3G-A sephadex G 200 and DEAE-cellulose column chromatography. The enzyme was stable in 50 mM Tris-HCl buffer pH 7.5 containing 60% glycerol at -18 degrees C. The pH optimum for the activity of DHAK from C. methylica was 7.5. The purified enzyme phosphorylated dihydroxyacetone four times faster than D,L-glyceraldehyde. The apparent MICHAELIS-MENTEN constants for dihydroxyacetone and D,L-glyceraldehyde were 0.011 mM and 0.024 mM. Other C3 compounds including glycerol were not phosphorylated. ITP and UTP were used as phosphate donors with a reaction rate of 11% and 3.1%, respectively, in relation to ATP, whereas the reaction rates of DHAK from C. methylica with CTP or GTP were much lower than 1%. The reaction of DHAK depends upon the presence of divalent cations in the assay. The highest activity was found with Mg2+ ions. The reaction rates with Co2+ or Ca2+ ions were only 57.3% and 30.3%, respectively, in relation to the assay with magnesium ions. Manganese chloride in the assay led to a complete loss of activity.

Dihydroxyacetone kinase of methanol-assimilating yeast. I. Regulation of dihydroxyacetone kinase from Candida methylica in situ

In order to investigate the control behaviour of dihydroxyacetone kinase of methanol-grown Candida methylica under nearly physiological conditions kinetic and regulatory studies were carried out in situ. Yeast cells were made permeable to substrate and reaction products by treatment with Triton X-100. Normal Michaelis-Menten kinetics resulted in dependence upon the dihydroxyacetone concentration, both at the pH optimum of 7.6 and near the physiological pH-value of 6.5. The Km obtained for dihydroxyacetone was 0.02 mM, independent of the pH-value. The plots of dihydroxyacetone kinase activity as a function of the ATP concentration revealed complex kinetic characteristics with plateau regions. The maximum reaction rate was reached only after a lag time both at pH 7.6 and concentrations of ATP higher than 5 mM and at pH 6.5 and concentrations of ATP higher than 1.25 mM. Among a great number of tested metabolites no inhibitors of dihydroxyacetone kinase were found. Dihydroxyacetone kinase activity depending upon energy charge according to Atkinson exhibited curves of the U-type. These results and further data concerning the regulation of other enzymes obtained with C. methylica and other yeasts were the basis to propose a preliminary overall model of fine control of the carbon and energy metabolism of methanol-utilizing yeasts.

Regulation of NAD+- and NADP+-linked isocitrate dehydrogenase in the obligate methylotrophic bacterium Pseudomonas W6

Cell-free extracts of the obligate methanol-utilizing bacterium Pseudomonas W6 catalyze the oxydation of isocitrate to alpha-ketoglutarate in the presence of NAD+ and NADP+. After electro-focusing of the crude extract of Pseudomonas W6 actually two distinct bands each of NAD+-linked isocitrate dehydrogenase (NAD+-IDH) and of NADP+-linked isocitrate dehydrogenase (NADP+-IDH) could be observed. The NAD+-IDH was completely separated from the NADP+-IDH by employing DEAE ion exchange chromatography and further purified by affinity chromatography using Cibacron blue F 3G-A. The NAD+-IDH was inhibited by a high energy charge, whereas the NADP+-IDH was found to be independent of energy charge. Consequently the NAD+-IDH showed the control behaviour of an enzyme of an energy-generating sequence which, however, equally fulfils a catabolic and an anabolic function. With respect to the inhibition by reduced pyridine nucleotides and alpha-ketoglutarate differences between NAD+-IDH and NADP+-IDH were also found. Only the NADP+-linked enzyme exhibited a feedback inhibition by its reaction products alpha-ketoglutarate and NADPH. This control behaviour gives evidence for the biosynthetic function of the NADP+-IDH. These results confer an amphibolic character to the sequence from citrate to alpha-ketoglutarate in the incomplete citric-acid cycle of Pseudomonas W6.

A critical analysis of kinetic data of 3-hexulosephosphate synthases. Michaelis-Menten or complex characteristics

Investigations of the 3-hexulosephosphate synthase (HPS) from different methylotrophic bacteria have revealed apparent discrepancies in kinetic behaviour. In 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. Both for Methylomonas M15 (SAHM et al. 1976) and Methylomonas aminofaciens 77a (KATO et al. 1977, 1978) MICHAELIS-MENTEN kinetics of the HPS were stated. 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 aminofaciens 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 oleovorans. In addition, causes which may obscure the detection of intermediary plateau regions are demonstrated.

Isolation of the ADP/ATP translocator from beef heart mitochondria as the bongkrekate-protein complex

1. The isolation of the ADP/ATP translocator from beef heart mitochondria as the bongkrekateprotein complex is described, using hydroxyapatite chromatography and gel filtration in Triton X-100 solution. 2. The inhibitor is bound to the protein prior to solubilization with detergent for protection against denaturation. Only the intact bongkrekate-protein passes easily through the hydroxyapatite column. Bongkrekate shileds the protein in contrast to carboxyatractylate only partially against proteinases present in the crude extract. 3. The isolated bongkrekate protein shows the same molecular weights in dodecylsulfate and Triton X-100, the same amino acid composition and the same isoelectric point as the earlier isolated carboxyatractylate-protein complex. It differs by its higher sensitivity against trypsin and thermolysin. 4. The identity of both proteins is demonstrated by interconversion of the bongkrekate-protein into the carboxyatractylate-protein. The process requires the catalysis by ADP or ATP, the natural substrates of the protein. 5. The formation of the extractable [3H]bongkrekate-protein complex in mitochondria requires the presence of ADP or ATP. 6. These data, the immunological studies presented earlier, and the differences in the reactivity of -SH groups of the isolated bongkrekate and carboxyatractylate complexes (to be published) indicate that both proteins represent different conformational states of the translocator protein (m-state and c-state).