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PubMed1976

[Control of RNA biosynthesis in rat liver. Some features of RNA biosynthesis during prolonged protein synthesis inhibition].

A drastic inhibition of protein biosynthesis in rat liver in vivo by cycloheximide (CHI) (0.3 mg/100 g of body weight) first caused an increase of RNA synthesis (after 1 hour), which was then followed by its decrease. Partial gradual restoration of the protein synthesis level was shown to be accompanied by a repeated increase of RNA synthesis (12 hs) and its normalisation after 24 hs. The first maximum of RNA synthesis increase in the isolated nuclei system was AU-type RNA synthesis (sensitive to alpha-amanitine), the second one was due to GC-type RNA synthesis (resistant to this toxin). Purified chromatine template activity in the system with E. coli RNA polymerase (by 14%) an hour after CHI treatment, but 3 hrs later was decreased and subsequently restored (12 hrs after CHI injection). The changes of RNA biosynthesis induced by prolonged protein synthesis inhibition suggest the existence of continuous RNA synthesis control in nuclei. This control is realized by translation system using the feed back principle.

Animals↗
PubMed1994

Inhibition of rat liver arginase by an intermediate in NO biosynthesis, NG-hydroxy-L-arginine: implications for the regulation of nitric oxide biosynthesis by arginase.

NG-hydroxy-L-arginine, an intermediate in the biosynthesis of nitric oxide (NO), has been found to be a uniquely potent competitive inhibitor of rat liver arginase. Among previously reported inhibitors of arginase and the eight arginine analogs tested herein, only NG-hydroxy-L-arginine was found to be strongly inhibitory. Significantly, the Ki (42 microM) for inhibition of rat liver arginase by NG-hydroxy-L-arginine was found to be 20-40-fold lower than the KM (1-1.7 mM) for its natural substrate, L-arginine. Since NG-hydroxy-L-arginine is the only known intermediate in the biosynthesis of NO from L-arginine, this finding may have significant implications for the regulation of NO levels in tissues or cells, such as liver or macrophages, which synthesize both NO and contain arginase.

Animals↗
PubMed2001

Biosynthesis and combinatorial biosynthesis of pikromycin-related macrolides in Streptomyces venezuelae.

Pikromycin-related macrolides have recently attracted significant research interest because they are structurally related to the semisynthetic ketolide antibiotics that have demonstrated promising potential in combating multi-drug-resistant respiratory pathogens. Cloning and in-depth studies of the pikromycin biosynthetic gene cluster from Streptomyces venezuelae have led to new avenues in modular polyketide synthases, deoxysugar biosynthesis, cytochrome P450 hydroxylase, secondary metabolite gene regulation, and antibiotic resistance. Moreover, the knowledge and tools used for these studies are proving to be valuable in the development of advanced technologies for combinatorial biosynthesis of new macrolide antibiotics. This review summarizes these new developments and introduces S. venezuelae as a powerful new system for secondary metabolite pathway engineering from bench-top genetic manipulation to product fermentation.

Anti-Bacterial Agents↗
PubMed1976

Studies on the biosynthesis of pulmonary surfactant. The role of the methylation pathway of phosphatidylcholine biosynthesis in primate and non-primate lung.

The relative importance of the choline incorporation and methylation pathways of phosphatidylcholine biosynthesis was studied in the rat, rabbit, rhesus monkey and human lung. In vitro studies showed that phosphatidylethanolamine methyltransferase activity in the lungs of all species was only a fraction of that in rat liver. In vivo experiments were carried out to study the incorporation of an intravenously administered equimolar mixture of L-[methyl-14C]-methionine and [methyl-3H] choline into lipid inthe lung and liver of the rabbit and monkey. Over 90% of the total radioactivity incorporated into lipid was found in phosphatidylcholine. In the liver, methionine incorporation was 40--71% of that of choline in the rabbit and 99--120% in the monkey while in the lungs of both species it was less than 3%. On a weight basis, choline incorporation in the lung was 2--4 times that in the liver. These findings suggest that the methylation pathway is of little quantitative significance in the biosynthesis of phosphatidylcholine in primate and non-primate lung.

Animals↗
PubMed1990

Hormonal regulation of complement biosynthesis in human cell lines--II. Upregulation of the biosynthesis of complement components C3, factor B and C1 inhibitor by interleukin-6 and interleukin-1 in human hepatoma cell line.

The effect of interleukin (IL)-6 and IL-1 on the biosynthesis of complement components C3, factor B, C2, C4 and C1 inhibitor (C1 inh), as well as that of albumin, was studied in vitro in human hepatoma-derived cell line, HepG2. Measuring the amounts of secreted complement proteins we detected a significant upregulation of C3 by both hormones. The enhancement of the factor B and especially that of C1 inh production was predominant by IL-6. In our experimental system neither IL-1 nor IL-6 affected the biosynthesis of C2 and C4. Albumin secretion was significantly decreased only in the simultaneous presence of IL-1 and IL-6. Detection of the changes in the amounts of C3- and factor B-specific mRNA of HepG2 cells suggests a pretranslational regulation by these cytokines. The secretion of C3 and factor B was markedly potentiated when IL-1 and IL-6 were added together. However only the gene expression of factor B, but not of C3, was found to reveal synergism. IL-6 enhanced the in vitro production of C3 in mouse hepatocytes as well. This effect was greatly potentiated in the presence of histamine.

Carcinoma, Hepatocellular↗
PubMed1983

Biosynthesis of pulmonary glycoconjugates--V. Biosynthesis of oligosaccharide inner core region of N-glycoprotein in lung microsomes.

Lung microsomes are able to synthesize dolichyl-mannosyl-phosphate, which stimulates the biosynthesis of a product (P1), soluble in chloroform/methanol/water (10:10:3, v/v). In presence of pulmonary dolichyl-mannosyl-phosphate, liver microsomes synthesized 3 mannosylated products: X1 product recovered in chloroform/methanol extract, X2 and X3 products soluble in chloroform/methanol/water (10:10:3, v/v). Mild acid hydrolysis of P1 product released one mannosylated oligosaccharide which remained at the origin in our solvent system, since two mannosylated oligosaccharides, released from products synthesized in liver, moved very slowly. Addition of N,N'-diacetyl [14C]chitobiosyl-pyrophosphoryl-dolichol to lung microsomes incubated with GDP-[3H]mannose stimulated the synthesis of a [3H, 14C]product extracted with chloroform/methanol (2:1, v/v). Mild acid hydrolysis of this product released [3H, 14C]oligosaccharide which moved very slowly on paper chromatography, in our solvent system. These results demonstrate that lung tissue can synthesize the oligosaccharide inner core region of N-glycoprotein with the sequence (Man)x-(GlcNac)2. But pulmonary dolichol pool is probably involved in other lipid biosynthesis pathways.

Animals↗
PubMed2005

Evolution of the indole alkaloid biosynthesis in the genus Hordeum: distribution of gramine and DIBOA and isolation of the benzoxazinoid biosynthesis genes from Hordeum lechleri.

Two indole alkaloids with defense related functions are synthesized in the genus Hordeum of the Triticeae. Gramine (3(dimethyl-amino-methyl)-indole) is found in H. spontaneum and in some varieties of H. vulgare, the benzoxazinoid 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) is detected in H. roshevitzii, H. brachyantherum, H. flexuosum, H. lechleri. Biosynthesis of DIBOA and of gramine was found to be mutually exclusive in wild Hordeum species, indicating that there was selection against simultaneous expression of both pathways during evolution. The full set of genes required for DIBOA biosynthesis in H.lechleri was isolated and the respective enzyme functions were analyzed by heterologous expression. The cytochrome P450 genes Bx2-Bx5 demonstrate a monophyletic origin for H. lechleri, Triticum aestivum and Zea mays. HlBx2-HlBx5 share highest homology to the orthologous genes of T. aestivum. In contrast, the branch point enzyme of the DIBOA pathway, the indole-3-glycerol phosphate lyase BX1, might have evolved independently in H. lechleri. In all Hordeum species that synthesize DIBOA, DNA sequences homologous to Bx genes are found. In contrast, these sequences are not detectable in the genomes of H. vulgare and H. spontaneum that do not synthesize benzoxazinoids.

Alkaloids↗
PubMed2001

Biosynthesis of the validamycins: identification of intermediates in the biosynthesis of validamycin A by Streptomyces hygroscopicus var. limoneus.

To study the biosynthesis of the pseudotrisaccharide antibiotic, validamycin A (1), a number of potential precursors of the antibiotic were synthesized in (2)H-, (3)H-, or (13)C-labeled form and fed to cultures of Streptomyces hygroscopicus var. limoneus. The resulting validamycin A from each of these feeding experiments was isolated, purified and analyzed by liquid scintillation counting, (2)H- or (13)C NMR or selective ion monitoring mass spectrometry (SIM-MS) techniques. The results demonstrate that 2-epi-5-epi-valiolone (9) is specifically incorporated into 1 and labels both cyclitol moieties. This suggests that 9 is the initial cyclization product generated from an open-chain C(7) precursor, D-sedoheptulose 7-phosphate (5), by a DHQ synthase-like cyclization mechanism. A more proximate precursor of 1 is valienone (11), which is also incorporated into both cyclitol moieties. The conversion of 9 into 11 involves first epimerization to 5-epi-valiolone (10), which is efficiently incorporated into 1, followed by dehydration, although a low level of incorporation of 2-epi-valienone (15) is also observed. Reduction of 11 affords validone (12), which is also incorporated specifically into 1, but labels only the reduced cyclitol moiety. The mode of introduction of the nitrogen atom linking the two pseudosaccharide moieties is not clear yet. 7-Tritiated valiolamine (8), valienamine (2), and validamine (3) were all not incorporated into 1, although each of these amines has been isolated from the fermentation, with 3 being most prevalent. Demonstration of in vivo formation of [7-(3)H]validamine ([7-(3)H]-3) from [7-(3)H]-12 suggests that 3 may be a pathway intermediate and that the nonincorporation of [7-(3)H]-3 into 1 is due to a lack of cellular uptake. We thus propose that 3, formed by amination of 12, and 11 condense to form a Schiff base, which is reduced to the pseudodisaccharide unit, validoxylamine A (13). Transfer of a D-glucose unit to the 4'-position of 13 then completes the biosynthesis of 1. Other possibilities for the mechanism of formation of the nitrogen bridge between the two pseudosaccharide units are also discussed.

Anti-Bacterial Agents↗
PubMed1981

Inhibitors of polyamine biosynthesis. 9. Effects of S-adenosyl-L-methionine analogues on mammalian aminopropyltransferases in vitro and polyamine biosynthesis in transformed lymphocytes.

Seven analogues of S-adenosyl-L-methionine were studied as inhibitors or substrates for mammalian spermidine and spermine synthases. One of these, S-(5'-deoxy-5'-adenosyl)-(+/-)-1-methyl-3-(methylthio)propylamine (5), showed a unique spectrum of activities on the polyamine biosynthesis enzymes. It was an inhibitor of S-adenosyl-L-methionine decarboxylase from rat liver and spermine synthase from bovine brain and rat ventral prostate. This compound was a substrate for the spermidine synthases from bovine brain and rat ventral prostate but not a substrate for the spermine synthases from these same sources. At concentrations of 0.2 mM and higher, compound 5 blocked the increases in polyamine levels and in [3H]thymidine incorporation induced by concanavalin A in cultured mouse lymphocytes. At approximately a 0.5 mM concentration of 5, the cellular polyamine levels and the rate of thymidine incorporation were similar to those of the unstimulated lymphocytes. Lower concentrations of 5 (0.02-0.1 mM) produced a dose-dependent increase in thymidine incorporation. A dose-dependent decrease in the cellular polyamine levels was observed in the range of 0.05-0.5 mM of the inhibitor. These results suggest that the effects of 5 on transformed lymphocytes are complex and may not be solely due to the inhibition of polyamine biosynthesis by this compound.

Animals↗
PubMed2003

Biosynthesis of structurally unique fungal metabolite GKK1032A(2): indication of novel carbocyclic formation mechanism in polyketide biosynthesis.

The biosynthesis of the antitumor agent GKK1032A(2) (1) has been investigated by administration of isotopically labeled ((13)C and (2)H) precursors to Penicillium sp. GKK1032. These studies showed that the backbone of 1 is constructed from l-tyrosine and a nonaketide chain flanked with five methyl groups probably by a polyketide synthase and a nonribosomal peptide synthetase hybrid. On the basis of the oxidation level of the starter unit and unusual 13-membered macroether formation between the tyrosine hydroxy group and the polyketide chain, novel cyclization mechanisms on the formation of a tricarbocyclic system and a macroether have been proposed. Involvement of a similar type of cyclization in the biosynthesis of structurally related metabolites is discussed.

Antibiotics, Antineoplastic↗
PubMed1968

Studies in phytosterol biosynthesis. Mechanism of biosynthesis of cycloartenol.

1. The mechanism of cycloartenol biosynthesis in leaves of Solanum tuberosum was investigated with the use of [2-(14)C,(4R)-4-(3)H(1)]mevalonic acid. 2. The (3)H/(14)C atomic ratio in cycloartenol was 6:6, the same as that in squalene; this eliminates lanosterol as a possible biosynthetic precursor of cycloartenol, and indicates that a hydrogen migration from C-9 to C-8 occurs. 3. Chemical isomerization of the cycloartenol to lanosterol ((3)H/(14)C ratio 5:6) and parkeol ((3)H/(14)C ratio 6:6) confirms the hydrogen migration from C-9 to C-8. 4. Possible mechanisms for the biosynthesis of cycloartenol and parkeol are discussed. 5. The (3)H/(14)C ratio for 24-methylenecycloartanol was 6:6, demonstrating that the hydrogen atom at C-24 is retained during alkylation of the cycloartenol side chain.

Carbon Isotopes↗
PubMed1998

Mycothiol biosynthesis and metabolism. Cellular levels of potential intermediates in the biosynthesis and degradation of mycothiol in mycobacterium smegmatis.

Mycothiol (MSH; 1-D-myo-inosityl-2-(N-acetyl-L-cysteinyl)amido-2-deoxy-alpha-D- glucop yranoside (AcCys-GlcN-Ins)) is a novel thiol produced at millimolar levels by mycobacteria and other actinomycetes that do not make glutathione. We developed methods to determine the major components of MSH (AcCys, Cys-GlcN, AcCys-GlcN, Cys-GlcN-Ins, GlcN-Ins) in cell extracts. Mycobacterium smegmatis was shown to produce measurable levels (nmol/g of residual dry weight) of AcCys ( approximately 30), Cys-GlcN-Ins (approximately 8), and GlcN-Ins (approximately 100) but not Cys-GlcN (<3) or AcCys-GlcN (<80) during exponential growth in Middlebrook 7H9 medium. The level of GlcN-Ins declined 10-fold in stationary phase and approximately 5-fold in 7H9 medium lacking glucose. Incubation in 10 mM AcCys produced 50- and 1000-fold increases in cellular Cys and AcCys levels, respectively, a 10-fold decrease in GlcN-Ins and a transient 3-fold increase in Cys-GlcN-Ins. These results exclude Cys-GlcN and AcCys-GlcN as intermediates in MSH biosynthesis and implicate GlcN-Ins and Cys-GlcN-Ins as key intermediates. Assay of GlcN-Ins/ATP-dependent ligase activity with Cys and AcCys as substrates revealed that Cys was at least an order of magnitude better substrate. Based on the cellular measurements, MSH biosynthesis involves assembly of GlcN-Ins, ligation with Cys to produce Cys-GlcN-Ins, and acetylation of the latter to produce MSH.

Chromatography, High Pressure Liquid↗
PubMed2005

Glucosamine-induced activation of glycogen biosynthesis in isolated adipocytes. Evidence for a rapid allosteric control mechanism within the hexosamine biosynthesis pathway.

Enhanced flux through the hexosamine biosynthesis pathway (HBP) induces insulin resistance and facilitates lipid storage through the up-regulation of enzyme mRNA levels. Both actions occur over several hours and require gene expression. We now identify a regulatory arm of the HBP that involves rapid allosteric activation of glycogen synthase (GS) and stimulation of glycogen biosynthesis (GBS). When insulin-pretreated adipocytes were exposed to 2 mM GlcN, incorporation of [14C]glucose into glycogen doubled by 10 min (t(1/2) of <5 min), whereas UDP-glucose levels were concomitantly decreased during this time (t(1/2) of 1.4 min; >90% depletion). Stimulation of GBS and depletion of UDP-glucose both correlated with an early and rapid rise in the levels of glucosamine-6-phosphate (GlcN-6-P), a known activator of GS. The lowering of GlcN-6-P levels by removing extracellular GlcN (>80% reduction by 45 min) was accompanied by the restoration of UDP-glucose levels. Prolonged GlcN treatment (20 min to 2 h) inhibited GBS, which corresponded to a massive intracellular accumulation of GlcN-6-P (t(1/2) of approximately 32 min; >1,400 nmol/g). From these data, we conclude the following. 1) GlcN treatment elevated intracellular GlcN-6-P levels within minutes, resulting in allosteric activation of GS, stimulation of GBS, and a reduction in steady-state levels of UDP-glucose due to increased precursor utilization. 2) Prolonged treatment with high concentrations of GlcN caused massive accumulation of GlcN-6-P that adversely affected cellular metabolism and reduced GBS. 3) The biphasic actions of GlcN on GBS may explain many of the discrepant reports on the role of the HBP in glycogen metabolism.

Adipocytes↗
PubMed2005

Biosynthesis of UDP-N-acetyl-L-fucosamine, a precursor to the biosynthesis of lipopolysaccharide in Pseudomonas aeruginosa serotype O11.

UDP-N-acetyl-L-fucosamine is a precursor to l-fucosamine in the lipopolysaccharide of Pseudomonas aeruginosa serotype O11 and the capsule of Staphylococcus aureus type 5. We have demonstrated previously the involvement of three enzymes, WbjB, WbjC, and WbjD, in the biosynthesis of UDP-2-acetamido-2,6-dideoxy-L-galactose or UDP-N-acetyl-L-fucosamine (UDP-l-FucNAc). An intermediate compound from the coupled-reaction of WbjB-WbjC with the initial substrate UDP-2-acetamido-2-deoxy-alpha-D-glucose or UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) was purified, and the structure was determined by NMR spectroscopy to be UDP-2-acetamido-2,6-dideoxy-L-talose (UDP-L-PneNAc). WbjD could then convert this intermediate into a new product with the same mass, consistent with a C-2 epimerization reaction. Those results led us to propose a pathway for the biosynthesis of UDP-L-FucNAc; however, the exact enzymatic activity of each of these proteins has not been defined. Here, we describe a fast protein liquid chromatography (FPLC)-based anion-exchange procedure, which allowed the separation and purification of the products of C-2 epimerization due to WbjD. Also, the application of a cryogenically cooled probe in NMR spectrometry offers the greatest sensitivity for determining the structures of minute quantities of materials, allowing the identification of the final product of the pathway. Our results showed that WbjB is bifunctional, catalyzing firstly C-4, C-6 dehydration and secondly C-5 epimerization in the reaction with the substrate UDP-D-GlcNAc, producing two intermediates. WbjC is also bifunctional, catalyzing C-3 epimerization of the second intermediate followed by reduction at C-4. The FPLC-based procedure provided good resolution of the final product of WbjD reaction from its epimer/substrate UDP-l-PneNAc, and the use of the cryogenically cooled probe in NMR revealed unequivocally that the final product is UDP-L-FucNAc.

Bacterial Proteins↗
PubMed2006

Inhibition of brassinosteroid biosynthesis by either a dwarf4 mutation or a brassinosteroid biosynthesis inhibitor rescues defects in tropic responses of hypocotyls in the arabidopsis mutant nonphototropic hypocotyl 4.

The nonphototropic hypocotyl 4 (nph4)/auxin response factor 7 (arf7) mutant of Arabidopsis (Arabidopsis thaliana) is insensitive to auxin and has defects in hypocotyl tropism, hook formation, differential leaf growth, and lateral root formation. To understand an auxin-signaling pathway through NPH4, we carried out screening of suppressor mutants of nph4-103 and obtained a dwarf suppressor mutant, suppressor of nph4 (snp2). snp2 had short hypocotyls in the dark condition and dark green and round leaves, short petioles, and more lateral shoots than the wild type in the light condition. The snp2 phenotypes were rescued by adding brassinolide to the growth medium in both light and dark conditions. Genetic mapping, sequence analysis, and a complementation test indicated that snp2 was a weak allele of DWARF4 (DWF4), which functions in brassinosteroid (BR) biosynthesis. snp2, which was renamed dwf4-101, exhibited photo- and gravitropisms of hypocotyls similar to those of the wild type with a slightly faster response in gravitropism. dwf4-101 almost completely suppressed defects in both tropisms of nph4-103 hypocotyls and completely suppressed hyponastic growth of nph4-103 leaves. Treatment with brassinazole, an inhibitor of BR biosynthesis, also partially rescued the tropic defects in nph4-103. Hypocotyls of nph4-103 were auxin insensitive, whereas hypocotyls of dwf4-101 were more sensitive than those of the wild type. dwf4-101 nph4-103 hypocotyls were as sensitive as those of dwf4-101. Auxin inducibility of massugu 2 (MSG2)/IAA19 gene expression was reduced in nph4-103. mRNA level of MSG2 was reduced in dwf4-101 and dwf4-101 nph4-103, but both mutants exhibited greater auxin inducibility of MSG2 than the wild type. Taken together, dwf4-101 was epistatic to nph4-103. These results strongly suggest that BR deficiency suppresses nph4-103 defects in tropic responses of hypocotyls and differential growth of leaves and that BR negatively regulates tropic responses.

Alleles↗
PubMed1998

(+)-Germacrene A biosynthesis . The committed step in the biosynthesis of bitter sesquiterpene lactones in chicory

The leaves and especially the roots of chicory (Cichorium intybus L. ) contain high concentrations of bitter sesquiterpene lactones such as the guianolides lactupicrin, lactucin, and 8-deoxylactucin. Eudesmanolides and germacranolides are present in smaller amounts. Their postulated biosynthesis through the mevalonate-farnesyl diphosphate-germacradiene pathway has now been confirmed by the isolation of a (+)-germacrene A synthase from chicory roots. This sesquiterpene cyclase was purified 200-fold using a combination of anion-exchange and dye-ligand chromatography. It has a Km value of 6. 6 &mgr;M, an estimated molecular mass of 54 kD, and a (broad) pH optimum around 6.7. Germacrene A, the enzymatic product, proved to be much more stable than reported in literature. Its heat-induced Cope rearrangement into (-)-beta-elemene was utilized to determine its absolute configuration on an enantioselective gas chromatography column. To our knowledge, until now in sesquiterpene biosynthesis, germacrene A has only been reported as an (postulated) enzyme-bound intermediate, which, instead of being released, is subjected to additional cyclization(s) by the same enzyme that generated it from farnesyl diphosphate. However, in chicory germacrene A is released from the sesquiterpene cyclase. Apparently, subsequent oxidations and/or glucosylation of the germacrane skeleton, together with a germacrene cyclase, determine whether guaiane- or eudesmane-type sesquiterpene lactones are produced.

Journal Article↗
PubMed2001

Biosynthesis of germacrene A carboxylic acid in chicory roots. Demonstration of a cytochrome P450 (+)-germacrene a hydroxylase and NADP+-dependent sesquiterpenoid dehydrogenase(s) involved in sesquiterpene lactone biosynthesis.

Sprouts of chicory (Cichorium intybus), a vegetable grown in the dark, have a slightly bitter taste associated with the presence of guaianolides, eudesmanolides, and germacranolides. The committed step in the biosynthesis of these compounds is catalyzed by a (+)-germacrene A synthase. Formation of the lactone ring is the postulated next step in biosynthesis of the germacrene-derived sesquiterpene lactones. The present study confirms this hypothesis by isolation of enzyme activities from chicory roots that introduce a carboxylic acid function in the germacrene A isopropenyl side chain, which is necessary for lactone ring formation. (+)-germacrene A is hydroxylated to germacra-1(10),4,11(13)-trien-12-ol by a cytochrome P450 enzyme, and is subsequently oxidized to germacra-1(10),4,11(13)-trien-12-oic acid by NADP+-dependent dehydrogenase(s). Both oxidized germacrenes were detected as their Cope-rearrangement products elema-1,3,11(13)-trien-12-ol and elema-1,3,11(13)-trien-12-oic acid, respectively. The cyclization products of germacra-1(10),4,11(13)-trien-12-ol, i.e. costol, were also observed. The (+)-germacrene A hydroxylase is inhibited by carbon monoxide (blue-light reversible), has an optimum pH at 8.0, and hydroxylates beta-elemene with a modest degree of enantioselectivity.

Alcohol Oxidoreductases↗
PubMed1975

Role of adenylate kinase in the regulation of macromolecular biosynthesis in a putative mutant of Escherichia coli defective in membrane phospholipid biosynthesis.

The regulation of macromolecular biosynthesis was studied in a temperature-sensitive mutant of Escherichia coli previously identified as containing a single mutation causing a thermolabile sn-glycerol-3-phosphate acyltransferase, the first enzyme of the pathway for phospholipid biosynthesis. When this mutant was shifted to a nonpermissive temperature, phospholipid synthesis, as well as ribonucleic acid, deoxyribonucleic acid, and protein synthesis, decreased in a coordinate manner, suggesting the existence of a common regulatory mechanism. During the same time that the rate of macromolecular synthesis was decreasing at the nonpermissive temperature, the intracellular concentration of adenosine 5'-triphosphate dropped dramatically and the concentration of adenosine monophosphate increased. The concentration of adenosine 5'-diphosphate dropped, but not as markedly. The decrease in macromolecular synthesis and the changes in the adenine nucleotide concentrations can now be attributed to a thermolabile adenylate kinase. The inactivation of adenylate kinase prevented the cell from converting adenosine 5'-monophosphate to adenosine 5'-diphosphate and consequently from making adenosine 5'-triphosphate. This in turn caused a decrease in the rate of macromolecular synthesis and cell growth. Adenylate kinase, therefore, is a key enzyme in controlling the rate of cell growth. The nature of the possible relationship between adenylate kinase and glycerol-3-phosphate acyltransferase is discussed.

Adenosine Triphosphate↗