The effect of glucose repression on the level of ribosomal-bound β-glucosidase

INDUCTION AND MULTI-SENSITIVE END-PRODUCT REPRESSION IN THE ENZYMIC PATHWAY DEGRADING MANDELATE IN PSEUDOMONAS FLUORESCENS

1. The first five enzymes involved in the degradation of mandelate in Pseudomonas fluorescens have been examined. 2. Induction is not significantly affected by glucose. 3. The first three enzymes form a group inducible by mandelate and repressible by benzoate, catechol and succinate. 4. The possibility that benzoate and catechol act as repressors only after they have been degraded to succinate is unlikely since mutants blocked at suitable points in the pathway have the same repression pattern as the wild type. 5. It is concluded that synthesis of the enzymes is subject to a multi-sensitive repression mechanism that can be independently activated by benzoate or catechol or succinate. 6. In each case the repression can be largely overcome by increasing the concentration of the inducer. 7. The enzymes of the first group are thus controlled by a dual system in which induction by the first substrate is opposed by repression exerted by the end product of the first group and by the products of succeeding groups.

Utilization of glucose and celloboise by the microflora of soil enriched with cellulose

The ability of soil microflora to utilize glucose or celloboise was found to depend on previous incubation of the soil with glucose, celloboise or cellulose. Glucose was utilized more rapidly than cellobiose in soil preincubated with glucose or cellobiose. The opposite situation was observed in soil preincubated with cellulose. In the presence of a mixture of both sugars the rate of utilization of one of them was decreased by the second and this decrease could be characterized as competitive inhibition. Glucose accumulated in the medium during utilization of cellobiose alone in soil preincubated with cellulose. This phenomenon was not observed during the utilization of cellobiose in soil preincubated with glucose or cellobiose.

Catabolite translational effects on the lac messenger RNA of Escherichia coli K12

The transcriptional and translational events occurring during the induction of the lac operon, were separated by blocking the translational step, either by aminoacid starvation or by addition of chloramphenicol. It was found that the carbon source used during the subsequent translation, affected the rate of beta-galactosidase synthesis. A decoordination effect on the production of enzymes of the lac system was also observed in high catabolite repression media, as well as in nitrogen limiting conditions. These findings suggested a similarity with the polarity phenomenon. In order to test this similarity, polarity suppressors of a Z- polar mutant were isolated. In one of these mutants, probably suA like, no carbon source effect was observed during the translational step. The induction kinetics in different media, after distinct pregrowth conditions, supported the idea that this mutant could be considered catabolite repression resistant only in certain restrictive conditions.

Accumulation of untranslated lactose-specific messenger ribonucleic acid during catabolite repression in Escherichia coli

When Escherichia coli K-12 Hfr.H was induced to synthesize beta-galactosidase in the presence of glucose, an untranslated lactose-specific mRNA (lac-mRNA), protected from decay, was found to accumulate progressively within the cells. The lac-mRNA accumulation was unaffected by the carbon source on which the cells had been grown before the induction. The amount of the lac-mRNA available for translation was affected by catabolite repression and 3':5'-cyclic AMP, but it remained unclear whether this was a direct effect on the formation of the lac-mRNA or a consequence of the effect on its translation.

Control of beta-glucosidases in schizophyllum commune

Intra- and extra-cellular enzymes of Schizophyllum commune which hydrolyze various β-glucosidic linkages were investigated. Low specific activities of enzymes hydrolyzing p-nitrophenyl-β-D-glucoside (PNPG) were always present. Confrontation of mycelium with cellobiose and certain other β-linked compounds for 18 h induced an extracellular PNPGase while intracellular PNPGase increased 10-fold. Glucose repressed PNPGase formation in vivo and also competitively inhibited substrate hydrolysis in vitro. Various stages in the life cycle of S. commune were examined for induction by cellobiose and repression by glucose. Both phenomena were demonstrable throughout development, but basidiospore germlings were most responsive to β-glucosidase induction. Induction appeared dependent on protein synthesis and respiration, since specific metabolic inhibitors prevented the process. Fractionation of cellobiose-induced mycelium extracts showed multiple components hydrolyzing PNPG. The major fraction also hydrolyzed cellobiose and laminarin. Purification of cellobiose-culture filtrates showed only one enzyme component and this was directly comparable to the major intracellular fraction. One of the minor intracellular components hydrolyzed laminarin and the second pustulan.

Intracellular Regulatory Mechanisms: Regulation in multicellular forms may be an elaboration upon the pattern evolved in microorganisms

The study of metabolic regulation in microorganisms has revealed several simple but efficient regulatory circuits. In one, the operation of an entire sequence of enzymes is controlled by the activity of the initial enzyme which contains a specific inhibitor site. When this site is combined with the endproduct of the sequence, the catalytic site is rendered inactive. In another, the formation of an entire sequence of enzymes is controlled by means of a cytoplasmic mediator which blocks the transcription of the genetic message (repression) when activated by the endproduct, or which allows the transcription (induction) when activated by the substrate of the first enzyme in the sequence. Additional circuits have been proposed for the regulation of RNA and DNA synthesis. The same regulatory devices could account, in part, for intracellular metabolic control in more complex animal and plant forms. However, superimposed upon these simple control circuits will be found others which take advantage of the greater degree of organization in these cells and of the possibilities for regulating gene function that are provided by the chromosomes. The pattern of proteins with special control sites, such as have evolved in the relatively simple controls found in bacteria, may also be found essential for intercellular controls involving nervous and humoral mechanisms.

METABOLIC CONTROL OF PENICILLINASE BIOSYNTHESIS IN BACILLUS CEREUS

Yip, Lily C. (University of Cincinnati, Cincinnati, Ohio), Ramesh Shah, and Richard A. Day . Metabolic control of penicillinase biosynthesis in Bacillus cereus . J. Bacteriol. 88: 297–308. 1964.—Penicillinase production in strains 5 and 5/B of Bacillus cereus in response to treatment by 6-aminopenicillanic acid (APA), penicillin G, (6- N -α-( p -benzyloxyphenoxy)-propionylamino-penicillanic acid, and cephalosporin C (CC) was found to be analogous to that seen in constitutive strains. Strain 5 did not release penicillinase into the medium to any great extent. Penicillinase production and the effect of the above penicillins on it were found to decline with increasing density of the culture. The penicillins were shown to accelerate or retard the production of penicillinase activity in strain 5 cells during pretreatment at 0 C and during incubation at 37 C. Strains 5 and 5/B gave qualitatively similar responses to penicillin treatment. At 0 C, the specific activity of penicillinase in strain 5 passes through a period of rapid increase at 0 hr and a period of little change at approximately 1 hr, followed by an increased rate of change towards 2 hr. The effect of APA or CC on specific activity of strain 5 cells during treatment at 0 C could not be reversed by one another, but Hg could reverse the increase caused by CC to some extent and the repression caused by APA. The production of penicillinase in the microconstitutive strain 5 of Bacillus cereus in response to treatment with CC was influenced by various inhibitors. 8-Azaguanine inhibited the production of the enzyme both during a pretreatment of the cells with CC at 0 C and during the subsequent incubation at 37 C. Actinomycin D, 6-azauracil, 6-thioguanine, and 2-thiocytosine inhibit the increase in penicillinase arising after the pretreatment at 0 C. 6-Azathymine has very little effect on the change of penicillinase activity. The CC-induced change occurring during the 0 C period was postulated to be a process at the level of protein biosynthesis itself; change at 37 C, constituting a delayed response, was considered a process at the level of messenger ribonucleic acid synthesis.

INDUCTION AND REPRESSION OF L-ARABINOSE ISOMERASE IN PEDIOCOCCUS PENTOSACEUS

Dobrogosz, Walter J. (University of Illinois, Urbana) and Ralph D. DeMoss. Induction and repression of l-arabinose isomerase in Pediococcus pentosaceus. J. Bacteriol. 85:1350-1355. 1963.-The inducible l-arabinose isomerase of Pediococcus pentosaceus can be rapidly and conveniently measured in whole-cell preparations by use of a standard colorimetric procedure originally developed for studies with cell-free enzyme preparations. The enzyme is measured by its ability to catalyze the isomerization of l-arabinose to l-ribulose. Whole cells suspended in a suitable buffer and pretreated with toluene were shown to exhibit this isomerase activity at a level comparable with that observed in cell-free enzyme preparations. Conditions for optimal induction of l-arabinose isomerase are described. In addition, it was determined that the formation of this enzyme is subject to repression by glucose, i.e., via catabolite repression.

GENETIC CONTROL OF β-GLUCOSIDASE SYNTHESIS IN SACCHAROMYCES LACTIS

Herman, Alberta (University of Wisconsin, Madison) and Harlyn Halvorson . Genetic control of β-glucosidase synthesis in Saccharomyces lactis . J. Bacteriol. 85: 901–910. 1963.—Both methyl-β- d -glucoside (2 × 10 −2 m ) and glucose (10 −3 m ) induced β-glucosidase synthesis in selected strains of Saccharomyces lactis . Genetic studies indicated the existence of a single locus specifically affecting β-methyl glucoside inducibility. Glucose-induced β-glucosidase synthesis, on the other hand, was nonspecific (other carbohydrases were simultaneously induced) and appeared to be controlled by more than one genetic factor. In both cases, noninducibility was dominant in diploids. The independent expression of these two modes of induction implied that these loci regulated β-glucosidase induction in a nonsequential manner.