Pattern Of Product Formation Research Articles

PRODUCT FORMATION PATTERNS AND THE PERFORMANCE IMPROVEMENT FOR MULTISTAGE CONTINUOUS STIRRED TANK FERMENTORS

The relationship between the product formation patterns and the performance improvement was studied for the multistage chemostat system. The performance evaluation was made based on the noninferior sets defined for the productivity and the product concentration. It is shown that when the strong product inhibition or the substrate inhibition occurs, the significant improvement can be attained by increasing the number of stages. It is also shown that the maximum product concentration attainable can be increased by increasing the number of stages for the case where either the cell maintenance coefficient or the product decomposition rate is nonzero. If the productivity is the only performance criterion, the performance improvement cannot be attained by increasing the number of stages for the growth-associated type of product formation, while it can be expected for the non-growth-associated type.

Metabolic effects of paraquat onSaccharomyces cerevisiae

Paraquat-tolerant cells ofSaccharomyces cerevisiae were selected by growing the cells in medium supplemented with paraquat either in a continuous selection culture with UV irradiation of the cells or in shaker flasks. When tranferred to fresh medium containing 1.0 mM paraquat, the selected cells showed growth rates and product formation patterns very similar to those of normal cells grown in a medium without paraquat. In the presence of paraquat, cells that had developed a tolerance were able to metabolize the fermentation products formed from glucose. Normal cells were unable to do so for considerable time.

Stability of solvent formation in Clostridium acetobutylicum during repeated subculturing

Clostridium acetobutylicum ATCC 824 was submitted to repeated subculturing at 24-hour intervals for 218 days. The organism retained its ability to form solvents, although the fermentation slowly became increasingly acidogenic during the first 200 days. Except for the initial spore inoculum, the cultures were not subjected to heat shocking between the serial transfers. When the inoculum volume was doubled from 3.3% to 6.7% after 200 days of subculturing, the product formation pattern quickly shifted back from acids to primarily butanol. Acetone production also resumed after being undetectable for more than 50 days. The relative formation of acetate and ethanol remained nearly constant throughout the experiments, while the formation of butyrate mirrored that of butanol.

CCK26-33 degrading activity in brain and nonneural tissue: a metalloendopeptidase.

Cholecystokinin octapeptide (CCK26-33) is metabolized by neural membranes with an initial cleavage to CCK29-33 and subsequent breakdown to CCK31-33 and CCK32-33; this pattern of proteolysis occurs on incubation with either P2 or purified lysed synaptosomal membranes. To determine whether the pattern of CCK26-33 proteolysis is unique to the brain and whether regional brain differences in its pathway or rate exist, we analyzed the proteolysis of CCK by synaptic membranes of various brain areas and cellular membranes of peripheral tissue. The pattern of degradation in brain did not differ among the regions studied. The overall proteolysis rate, as measured by the formation of tryptophan, was higher in the striatum than in the cortex, although CCK29-33 was formed at the same rate in both areas. In nonneural tissue, the rate of degradation was highest in liver membranes and lowest in pancreatic acinar cell preparations. Thus, it appears that degradative peptidases are not necessarily colocalized with CCK receptors. The pattern of product formation is the same in peripheral compared with CNS membranes; thus, the degradative pathway does not appear to be unique to brain tissue. The enzyme present in synaptic membranes that is responsible for CCK29-33 formation requires a metal ion and sulfydryl groups for the catalysis and thus is a metalloendopeptidase. Furthermore, its activity is inhibited by Ac-Gly-Phe-Nle-al, a peptide aldehyde whose sequence bears some homology to the amino acid sequence in the region of CCK26-33 that is cleaved by this enzyme.

Metabolic fate of platelet-activating factor in neutrophils.

1-O-[3H]Alkyl-2-acetyl-sn-glycero-3-phosphocholine (1-O-[3H]alkyl-2-acetyl-GPC) incubated with rabbit polymorphonuclear leukocytes was metabolized to 1-O-alkyl-2-acyl-GPC containing long chain groups at the 2 position. Within 5 min, 60% of the total label added to the cell suspension was found in the 1-O-[3H]alkyl-2-acyl-GPC. At earlier time points, 1-O-[3H]alkyl-2-lyso-GPC was present. No metabolites were detected that would indicate the ether bond had been cleaved or the polar head group had been altered by the cells. At subaggregating and subdegranulating concentrations of labeled 1-O-[3H]alkyl-2-acyl-GPC, the same pattern of product formation was observed. Furthermore, when 1-O-[3H]alkyl-2-lyso-GPC was added to the cells, it was taken up and acylated in the same manner as that from 1-O-alkyl-2-acetyl-GPC. The nature of the long chain acyl residues incorporated into the 2 position was then examined by argentation chromatography and high performance liquid chromatography. Argentation chromatography of 1-O-[3H]alkyl-2-acyl-3-acetylglycerols obtained from 1-O-[3H]alkyl-2-acyl-GPC after acetolysis indicated that mono-, di-, and tetraenoic fatty acids were the predominant molecular species being incorporated into the 2 position of the molecule (18, 55, and 18%, respectively). Furthermore, high performance liquid chromatographic analysis using synthetic 1-O-alkyl-2-acyl-GPC standards indicated that three fatty acids, linoleic, arachidonic, and oleic (50, 15, and 12%, respectively), were the major chains being incorporated into the 1-O-hexadecyl-linked species. Analysis of 1-O-[3H]alkyl-2-acyl-GPC derived from exogenously added 1-O-[3H]alkyl-2-lyso-GPC revealed the same distribution of acyl groups linked to the 2 position. The findings are consistent with a pathway in which two enzymatic activities are responsible for the metabolism of exogenous platelet-activating factor in the rabbit neutrophils: one that hydrolyzes the acetyl residue (acetylhydrolase) and another that transfers a fatty acyl chain to the 1-O-alkyl-2-lyso-GPC formed (possibly acyl-CoA:1-O-alkyl-2-lyso-GPC acyltransferase). These events appear to play an important role in inactivating this potentially lethal phospholipid.

Calcium alginate immobilized cells of clostridium acetobutylicum for solvent production

Immobilized vegetative cells ofC. acetobutylicum has a similar product formation pattern when incubated in a simple glucose-salts solution as ordinary growing cells. If vegetative cells of the organism are immobilized in the solvent production phase, solvents are continuously produced on extended incubation.

Non enzymic formation of nerolidol from farnesyl pyrophosphate in the presence of bivalent cations

1- 3H Farnesyl pyrophosphate is hydrolyzed non enzymically at neutral or alkaline pH in the presence of Mg 2+ or Mn 2+. The pattern of product formation differs for these two ions. In the presence of Mn 2+, nerolidol is practically the only reaction product, whereas in the presence of Mg 2+ the hydrolysis products are nerolidol and farnesols. The effect of Mg 2+ is pH dependent. The formation of nerolidol from mevalonic acid or other precursors of isoprenoids may thus be explained as a non enzymic reaction of farnesyl pyrophosphate.

The vanadium-pentoxide-catalyzed oxidation of pentenes: III. The role of the catalyst

Investigations of changes in the surface area and phase composition of vanadium pentoxide catalysts in contact with reacting mixtures of pent-2-ene with oxygen have been made. As a pumice-supported vanadium pentoxide catalyst is used, pentavalent vanadium is reduced gradually to tetravalent vanadium. When the latter attains a critical concentration a phase change occurs, reaction with the support giving sodium vanadyl vanadate. Simultaneously, sudden increases in the surface area and in the rate of oxidation of pentene occur but the selectivity of the oxidation falls, many new products being formed. Further use of the catalyst leads eventually to its deactivation. Vanadium pentoxide in contact with mixtures of oxygen and unsaturated hydrocarbons contains, therefore, V4+ ions as well as V5+ ions. The pattern of product formation and the physicochemical properties of the catalyst support strongly the suggestion that the mechanism of oxidation involves reaction of the fuel with oxide ions, the catalyst being reduced. The function of gaseous molecular oxygen is to reoxidize the reduced catalyst and this step is rate-determining. It would appear that this mechanism is a general one for the oxidation of unsaturated hydrocarbons over vanadium pentoxide. On old catalysts containing sodium vanadyl vanadate, however, the mechanism differs considerably; free-radical chain reactions in which molecular oxygen is the active oxidant become important.

The vanadium-pentoxide-catalyzed oxidation of pentenes: II. Straight-chain pentenes

The oxidation of pent-2-ene in the temperature range 250–450°C over a freshly prepared vanadium pentoxide catalyst produces acetaldehyde, propionaldehyde, ethylene, propylene, trans-2,3-epoxypentane, acetone, and carbon dioxide. Use of the catalyst for approximately 5 hr causes a marked and sudden change in the pattern of product formation. The oxidation becomes more rapid but much less selective, at least 14 extra products being formed. The oxidation of pent-1-ene under similar conditions proceeds largely via isomerization to pent-2-ene and oxidation of the latter. On a “new” catalyst, the products are probably formed by interaction of adsorbed pentene with O2−. An overall mechanism results in which the catalyst itself is reduced by the adsorbed pentene and re-oxidized by gaseous oxygen. V5+ is therefore the active oxidant. On an “old” catalyst, however, gaseous molecular oxygen attacks the adsorbed pentene directly and the oxidation acquires free-radical chain character with resultant loss of selectivity. It is therefore possible to reconcile the apparently contradictory “oxidation-reduction” and “hydroperoxylation” mechanisms for the oxidation of unsaturated hydrocarbons over vanadium pentoxide.