Conversion Of PC Research Articles

Investigation of the main regularities of glycolysis of polycarbonate plastic during catalysis by basic agents

This research focuses on analyzing how different primary catalysts affect the glycolysis of plastic made from bisphenol A (PC) polycarbonate. It was found that the process of chemical decomposition of PC under the influence of ethylene glycol (EG) leads to the formation of products with high added value: bisphenol A (PC monomer, BPA), BPA, and ethylene carbonate or ethylene glycol co-ethers (BPA monohydroxyethyl ether, MHE-BPA; BPA bishydroxyethyl ether, BHE-BPA). A quantitative assessment of the yields of the reaction products was also carried out. The yield of products at 100% PC conversion was 33% for BPA, 50% for MHE-BPA, and 17% for BHE-BPA. The effectiveness of using various alkalis depending on the type of metal was also compared within the context of this investigation.

Hydrodeoxygenation of Oxygen-Containing Aromatic Plastic Wastes into Cycloalkanes and Aromatics.

Chemical recycling and upcycling offer promising approaches for the management of plastic wastes. Hydrodeoxygenation (HDO) is one of the appealing ways for conversion of oxygen-containing plastic wastes, including polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), polyphenyl ether (PPO), and polyether ether ketone (PEEK), into cyclic alkanes and aromatics in high yields under mild reaction conditions. The challenge lies in achieving C-O activation while preserving C-C bonds. In this review, we highlight the recent advancements in catalytic strategies and catalysts for the conversion of these oxygen-containing plastic wastes into cycloalkanes and aromatics. The reaction systems, including multi-step routes, direct HDO and transfer HDO methods, are exemplified. The design and performance of HDO catalysts are systematically summarized and compared. We comprehensively discuss the functions of the catalysts' components, reaction pathway and mechanism to gain insights into the HDO process for efficient valorization of oxygen-containing plastic wastes. Finally, we provide perspectives for this field, with specific emphasis on the non-noble metal catalyst design, selectivity control, reaction network and mechanism studies, mixed plastic wastes management and product functionalization. We anticipate that this review will inspire innovations on the catalytic process development and rational catalyst design for the HDO of oxygen-containing aromatic plastics to establish a low-emission circular economy.

Abstract B051: Investigating lipid homeostasis in pancreatic ductal adenocarcinoma under tumor-like stress

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a 5-year survival rate of only 10%. One hallmark of PDAC’s tumor microenvironment is dense desmoplasia, due to abnormal accumulation of extracellular matrix and proliferative fibroblasts. During tumorigenesis, pancreatic stellate cells (PSCs) obtain myofibroblast-like signatures and contribute to the fibrotic environment of PDAC. Desmoplasia-induced hypovascularity severely limits oxygen and nutrient delivery. Our laboratory revealed that hypoxia is prominent even at the pancreatic intraepithelial neoplasia (PanIN) stage, a dominant precursor lesion of PDAC. Hypoxia inhibits oxygen-dependent metabolic processes. For example, unsaturated lipid biosynthesis relies on oxygen to maintain desaturase enzymatic activities. Hypoxia also stimulates lipid uptake. Previous studies demonstrated that RAS-transformed cells preferentially import unsaturated lysophosphatidylcholines (LPCs) from culture media. However, in a nutrient-limited fibrotic environment, the potential source of lipids is unclear. Interestingly, a lipidomic study of a PSC secretome displayed a significant amount of LPCs, suggesting that PSCs are the potential lipid source in the PDAC microenvironment. Our data indicate that exogenous unsaturated lipids sustain PDAC cell viability under hypoxia and nutrient deficiency. Moreover, we find PDAC cell survival under tumor-like stress is enhanced in PSC conditioned medium, but not in delipidated conditioned medium. Strikingly, we show that cancer-associated fibroblasts do not experience hypoxic stress as much as adjacent malignant epithelium cells in vivo, suggesting cancer-associated fibroblasts provide unsaturated (and other) lipids to PDAC cells. Based on our lipidomic mass spectra of PSC conditioned medium, we determined that LPCs are actively utilized by PDAC cells for phosphatidylcholine and triglyceride regeneration. By inhibiting LPC to PC conversion with the drug TSI-01, which targets LPCAT (acyltransferase), unsaturated LPC no longer sustains cancer cell survival and ER stress is reactivated. In this study, we demonstrated metabolic crosstalk between fibroblasts and PDAC cells under stress conditions. Our findings revealed a novel metabolic inhibitor to disrupt the metabolic crosstalk between PSC and pancreatic cancer cells which might benefit developing combinatorial therapy of PDAC. Citation Format: Xu Han, Michelle Burrows, Laura Kim, Clementina Mesaros, John Tobias, Brian Keith, Celeste Simon. Investigating lipid homeostasis in pancreatic ductal adenocarcinoma under tumor-like stress [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B051.

Polycarbonate ethanolysis with imidazolium-based ionic liquids: Recovery of high-purity BPA and value-added by-product

Depolymerization using ionic liquids (ILs) is an efficient and eco-friendly method for recycling waste poly(bisphenol A carbonate) (PC). To use IL for PC ethanolysis, the effect of IL structure on PC depolymerization should be investigated. In this study, we investigated PC ethanolysis using imidazolium-based ILs with different alkyl chain lengths (ethyl, butyl, and hexyl groups) as both the catalyst and solvent to afford the monomer bisphenol-A and a value-added byproduct, diethyl carbonate. 1-Ethyl-3-methyl imidazolium acetate ([EMIM][Ac]) exhibited the highest depolymerization efficiency, and an additional wash step increased the purity of the recovered BPA. A 100 % PC conversion rate, 90.9 % BPA yield, 99.9 % BPA purity, and 99 % [EMIM][Ac] reusability over five depolymerization cycles were observed in the PC ethanolysis using [EMIM][Ac]. In addition, recovered BPA behaved identically to commercially available BPA in the polymerization of PC. This strategy could help reduce the worldwide production of new BPA for PC synthesis.

One-step DMC synthesis from CO2 under catalysis of ionic liquids prepared with 1,2-propylene glycol

Three quaternary ammonium ionic liquids with strong nucleophilicity and distinctive structures were synthesized with high yield and purity based on the 1,2-propylene glycol anion (CH3CH2OHCH2O-) derived from transesterification products. Dimethyl carbonate (DMC) was in turn produced via a one-step reaction among propylene oxide (PO), CO2, and methanol (MeOH) by using the synthesized ionic liquids. The involved two-stage catalytic reaction of PO-CO2 cycloaddition and PC-MeOH transesterification was implemented without catalyst separation. Under mild conditions, the PO conversion reached 99.0%, with a PC yield of 99.0%, and a TON value of 119.5. Following the cycloaddition, MeOH was immediately introduced to achieve a PC conversion of 71.2%, a selectivity to DMC above 99%, and a TON value of 57.4 for the transesterification reaction. The influences of temperature as well as time for cycloaddition and transesterification were investigated. Cycloaddition of CO2 with various epoxides was also examined and all showed good performance. By taking advantage of the decomposability of as-prepared ionic liquids and the recyclability of decomposition products, a new catalyst circulation process was designed to complete the full cycle without introduction of any impurities into the product system.

A tailored IL@MOF catalyst for the rapid chemical fixation of CO2 using fixed-bed reactor based on the coupling of reaction and separation under ambient conditions

It is of great significance to valorize anthropogenic CO2 into commercially attractive production. Herein, a novel catalyst was designed using the ILs and MOFs for the efficient CO2 cycloaddition reaction. The obtained IL@MIL-101(Cr) catalyst exhibits high catalytic efficiency (the per pass conversion of PC is about 30% and selectivity is over 99%) under ambient conditions. The mechanism reveals that the synergistic effect of ILs and MOF promotes the apparent reaction rate of the catalyst. The coupling of reaction and separation could be realized by introducing the mixture of CO2 and PO into the fixed-bed reactor with the precisely designed catalyst.

Recyclable nanocomposites for carbon dioxide fixation and membrane separation using waste polycarbonate

In this study, polymer nanocomposite membranes with recyclability were developed to achieve good mechanical properties and gas permeability in the consumption of a recycled polymeric material. The newly developed process has been realized through the conversion of waste PC to afford key intermediates containing alkoxysilane and phenolic groups. The alkoxysilanes would act as the nucleation sites for sol–gel reactions, whereas the phenolic groups further provided active hydrogens for click reactions in the production of polyurethane/silica (PU/SiO2) nanohybrids, exhibiting microcavity to facilitate gas molecules diffusion for membrane with improved gas permeability. Moreover, the additional use of aliphatic polycarbonate polyol provided enhanced CO2 solubility for gas separation membranes of the PU/SiO2 nanohybrids with a PCO2 permeability of 24.02 barrer and a selectivity of 32.85 (αCO2/N2), which approached the 2008 Robeson upper bounds. Moreover, the joint presence of polycarbonate polyol and silica in the nanohybrids led to high-performance elastomeric properties, with tensile strengths of 35.5 MPa and over 700 % elongation at break, results that exceeded those of previously reported PU-based gas separation membranes. Notably, this PC recycling process featured the newly formed carbamate groups as the reaction sites, enabling the recyclability of PU/SiO2 nanohybrids as the gas separation membranes for CO2 capture and storage in post-consumption materials.

Dynamic and adaptive membrane lipid remodeling in leaves of sorghum under salt stress

Salt stress limits plant growth and development. In this study, changes in membrane lipids were investigated in leaves of sorghum seedlings subjected to salt stress (150 mmol L−1 NaCl). Galactolipids (DGDG and MGDG) accounted for more than 65% of the total glycerolipids in sorghum leaves. The predominance of C36 molecular species in MGDG suggested that sorghum is an 18:3 plant. Under NaCl treatment, the content of major phospholipids (PC and PE) increased, accompanied by the activation of their metabolism pathways at the transcriptional level. In contrast, the proportion of MGDG and PG dropped drastically, leading to a decreased ratio of plastidic to non-plastidic lipids. An adjustment of glycerolipid pathway between the cytosolic and plastidic compartments was triggered by salt stress, as reflected by the increased conversion of PC to PA, providing precursors for galactolipid synthesis. The elevated DGDG resulted in increased DGDG/MGDG and bilayer/non-bilayer lipid ratios. The double-bond index of PC, PE, and DGDG increased markedly, evidently owing to the increased expression of FAD3 and FAD8. These findings will be helpful for understanding dynamic membrane lipid changes and adaptive lipid remodeling in sorghum response to salt stress.

Intensifying the PC conversion in the raceway by means of coke oven gas

Among numerous measures to accelerate the PC conversion within the blast furnace (BF) raceway, local increase of oxygen concentration is the most common one. On the other hand, the presence of cold media (oxygen) in the vicinity of the coal stream might affect its ignition and combustion negatively. A minor amount of coke oven gas (COG) may increase the temperature and consequently accelerate the coal conversion. To examine this effect, laboratory trials under blast furnace simulating conditions were performed using the Multifunctional Injection Rig for Ironmaking (MIRI). The results of the simulation testified a higher conversion degree of coal while adding the COG. The temperature increase is measurable in the reaction chamber and the off-gas stream. Optical microscopy of the original PC particles and residues after reaction confirm the findings of the off-gas analysis and the increase in temperature during the experiments with addition of COG. The thermogravimetric analysis was applied to determine and to compare the behaviour of coal in different atmospheres including an atmosphere with COG. A stand at one tuyère at a modern BF was erected and tests were performed targeting the observation of the ignition behaviour of coal at different COG rates, using a camera image analysis system. Laboratory trials under blast furnace raceway simulating conditions showed, that even a small amount of COG significantly improves the PC conversion degree. A new technology of PC injection, including addition of small amount of COG to the PC transporting gas, aimed at neutralization of the oxygen local cooling effect, elaborated, justified and tested.

Synthesis of dimethyl carbonate by transesterification reaction using ceria-zinc oxide catalysts prepared with different chelating agents

This paper reports the use of novel ceria-zinc catalyst for the preparation of dimethyl carbonate (DMC) using transesterification of PC with methanol. Ceria-zinc oxide catalysts were prepared by a sol-gel method using citric acid, oxalic acid and tartaric acid as chelating agents (named as CZC, CZO, and CZT, respectively). The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, FTIR, SEM-EDX, ICP-OES, and CO2-temperature program desorption. Experimental results revealed that the catalytic performance of CZC was closely related to the surface area and presence of basic sites in the catalyst. CZC showed high selectivity and PC conversion. Effects of operating parameters such as methanol/PC molar ratio, catalyst dose, reaction temperature, reaction time were studied. The reusability of CZC as a catalyst for DMC selectivity and PC conversion with turn-over frequency (TOF) was also studied.

Production and Scale-up of phosphatidyl-tyrosol catalyzed by a food grade phospholipase D

Highly purified phosphatidyl-tyrosol was obtained by using a food grade phospholipase D from Actinamadure sp. transphosphatidylation in a GRAS (Generally Recognized As Safe) biphasic medium. The reaction medium, comprised of an aqueous phase and ethyl butyrate, has been considered as an alternative to other biphasic systems previously reported utilizing more harmful organic solvents. The purpose of the present study was to purify phosphatidyl-tyrosol from a transphosphatidylation reaction mixture by using a procedure readily scalable to obtain a new valuable food ingredient. Initially, phosphatidyl-tyrosol was purified via semi-preparative HPLC equipment to be used as analytical standard. The best results of the transphosphatidylation reaction were obtained for two different PC concentrations, namely 83 and 166mmol/L, with PC conversion of ca. 97 and 94% (w/w) and a final phosphatidyl-tyrosol concentration of 81 and 157mmol/L, respectively. Finally, the procedure was scaled-up and 40g of highly purified phosphatidyl-tyrosol (97% (w/w)) were readily purified by centrifugation without involving the utilization of organic solvents.

Mixtures of synthetic organic dyes in a photoelectrochemical cell

Spectroscopic and photoelectric properties of phthalocyanine (Pc), tetranaphtyloporphyrin (TNP) and merocyanine (Me) and their mixtures have been studied. Dyes dissolved in polyvinyl alcohol in dimethylsulfoxide were immersed in a semiconducting/metallic photoelectrochemical cell. Absorption, fluorescence and photoacoustic spectroscopies have been used as methods to follow deactivation pathways of radiative and non-radiative processes of excited states as a competitive processes to charge separation process. The dependence of photovoltage signal on excitation wavelength (photovoltage action spectrum), kinetics of photocurrent rise and decay in second time scale have been presented. Electric parameters of the photoelectrochemical cell with dyes (conductivity, capacitance) and their mixtures in the dark and upon illumination have been estimated. It was shown that all investigated dyes are able to generate photosignal but the values of photocurrent generated were dependent on the dye used in the experiment. The complexity of photoconversion process in the electrochemical cell fulfilled with the dye mixtures has been discussed. The presence of Me dye was found to improve TNP photovoltaic effect, whereas weak enhancement of photoeffects were observed in photoelectrochemical cell based on Me and Pc. This different tetraphenyloporphyrin and Pc conversion effectiveness in the presence of Me was discussed in aspects of various mechanisms of interaction between dyes. It has been indicated that dye aggregation, energy transfer, charge recombination and other processes can lead to improvement or inhibition of the photovoltaic effects and of the conversion effectiveness depending on the composition of dyes embedded in an electrochemical cell.

Biosynthesis of triacylglycerols containing ricinoleate in castor microsomes using 1-acyl-2-oleoyl-sn-glycero-3-phosphocholine as the substrate of oleoyl-12-hydroxylase.

We have examined the biosynthetic pathway of triacylglycerols containing ricinoleate to determine the steps in the pathway that lead to the high levels of ricinoleate incorporation in castor oil. The biosynthetic pathway was studied by analysis of products resulting from castor microsomal incubation of 1-palmitoyl-2-[14C]oleoyl-sn-glycero-3-phosphocholine, the substrate of oleoyl-12-hydroxylase, using high-performance liquid chromatography, gas chromatography, mass spectrometry, and/or thin-layer chromatography. In addition to formation of the immediate and major metabolite, 1-palmitoyl-2-[14C]ricinoleoyl-sn-glycero-3-phosphocholine, 14C-labeled 2-linoleoyl-phosphatidylcholine (PC), and 14C-labeled phosphatidylethanolamine were also identified as the metabolites. In addition, the four triacylglycerols that constitute castor oil, triricinolein, 1,2-diricinoleoyl-3-oleoyl-sn-glycerol, 1,2-diricinoleoyl-3-linoleoyl-sn-glycerol, 1,2-diricinoleoyl-3-linolenoyl-sn-glycerol, were also identified as labeled metabolites in the incubation along with labeled fatty acids: ricinoleate, oleate, and linoleate. The conversion of PC to free fatty acids by phospholipase A2 strongly favored ricinoleate among the fatty acids on the sn-2 position of PC. A major metabolite, 1-palmitoyl-2-oleoyl-sn-glycerol, was identified as the phospholipase C hydrolyte of the substrate; however, its conversion to triacylglycerols was blocked. In the separate incubations of 2-[14C]ricinoleoyl-PC and [14C]ricinoleate plus CoA, the metabolites were free ricinoleate and the same triacylglycerols that result from incubation with 2-oleoyl-PC. Our results demonstrate the proposed pathway: 2-oleoyl-PC-->2-ricinoleoyl-PC-->ricinoleate-->triacylglycerols. The first two steps as well as the step of diacylglycerol acyltransferase show preference for producing ricinoleate and incorporating it in triacylglycerols over oleate and linoleate. Thus, the productions of these triacylglycerols in this relatively short incubation (30 min), as well as the availability of 2-oleoyl-PC in vivo, reflect the in vivo drive to produce triricinolein in castor bean.

Text Jumbler PCM Blondel, N Brick, G Horrocks & N McBride An authoring package for the PC which runs on MS DOS and RM Nimbus machines with partial IBM emulation. It can also be used on Macintosh machines with PC conversion programmes such as PC Soft. Available fromText Jumbler, 4 Station Road, Leiston, Suffolk, IP16 4HD.

Text Jumbler PCM Blondel, N Brick, G Horrocks & N McBride An authoring package for the PC which runs on MS DOS and RM Nimbus machines with partial IBM emulation. It can also be used on Macintosh machines with PC conversion programmes such as PC Soft. Available fromText Jumbler, 4 Station Road, Leiston, Suffolk, IP16 4HD. - Volume 4 Issue 7

Lipid trafficking between high density lipoproteins and Babesia divergens‐infected human erythrocytes

A two-fold increase in the amount of phospholipids was observed in Babesia divergens infected human red blood cells. In vitro incubation with [32P]-phosphorus and [3H]-glycerol demonstrated that B divergens has the ability to synthesize the phospholipid backbone. On the other hand, the low incorporation of [14C]acetate indicated the absence of a de novo fatty acid synthesis and suggested the necessity of an exogenous lipid source for the parasite. Several intra-erythrocytic growth cycles of B divergens could be achieved in vitro, using a serum-free medium supplemented only with fractions of human high density lipoproteins (HDL). At an HDL concentration of 0.5 mg/ml (protein concentration) and with a 1% starting parasitaemia, parasite growth was similar to that observed under standard culture conditions with 10% human serum, at least for the first 24 h, a time equivalent to three parasite erythrocytic life-cycles. Lipid transfer from HDL to the intra-erythrocytic parasites was demonstrated by uptake and exchange of fluorescent NBD-phosphatidylcholine (NBD-PC) loaded HDL at different temperatures. Kinetic experiments with [3H]-oleyl-PC-loaded HDL demonstrated a unidirectional transfer of lipids from radiolabelled HDL to the parasite; partial conversion of PC to phosphatidylethanolamine (PE) was also observed. In the semi-defined medium, the HDL fraction appeared to be the major source of lipids for the growth of B divergens in human erythrocytes.

In vitro phosphorylation of phosphatidylethanolamine N-methyltransferase by cAMP-dependent protein kinase: lack of in vivo phosphorylation in response to N6-2′-O-dibutryladenosine 3′,5′-cyclic monophosphate

Phosphorylation of rat liver phosphatidylethanolamine (PE) N-methyltransferase by cAMP-dependent protein kinase was investigated. The 18 kDa methyltransferase was found to be phosphorylated in vitro by cAMP-dependent protein kinase on a serine residue. The stoichiometry of phosphate incorporation reached a maximum of 0.25 mol phosphate/mol methyltransferase at 30 min. Resolution of the phosphorylated methyltransferase by two-dimensional gel electrophoresis showed that two isoproteins were substrates. Phosphorylation of the purified PE N-methyltransferase for up to 1 h had no effect on the methylation of PE, PMME or PDME. To test for in vivo phosphorylation, isolated rate hepatocytes were exposed to 0.5 mM N6-2'-O-dibutryladenosine 3':5'-cyclic monophosphate (DiB-cAMP) and the phosphorylation state of microsomal proteins evaluated by two-dimensional gel electrophoresis, nitrocellulose blotting and autoradiography. The same nitrocellulose blots were probed with a rabbit anti-PE N-methyltransferase antibody, immunochemically stained and aligned with the autoradiogram. No phosphorylated proteins co-migrated with the methyltransferase under non-phosphorylating conditions, or when hepatocytes were exposed to the cAMP analogue for up to 2 h. Oddly, DiB-cAMP increased both PE- and PMME-dependent activity in isolated microsomes, but decreased PE to PC conversion measured in intact hepatocytes. The results indicated that PE N-methyltransferase is poorly phosphorylated by cAMP-dependent protein kinase in vitro, and is not phosphorylated in intact hepatocytes treated with a cAMP analogue.

Influence of salinity on 3H-serine metabolism. Study of 3H-serine incorporation into lipids of the chinese crab Eriocheir sinensis

1. 1. 3H-serine incorporation into phospholipids isolated from hemolymph, hepatopancreas, gills and muscle was determined for chinese crab Eriocheir sinensis maintained in media of extreme salinities. 2. 2. 3H-serine was mainly incorporated into phospholipids of hepatopancreas and gills. 3. 3. Decarboxylation of PS to PE occurs in these tissues. In addition, successive N-methylation of PE to PC takes place in hepatopancreas. The PS→PE→PC conversion was strongly activated when crabs were transferred from fresh water to sea-water. 4. 4. The roles of PS metabolism and of the N-methylation pathway of PE to PC in osmoregulation by these crabs are discussed.

Reactions of carbonyl compounds in the presence of phase-transition catalysts. 5. Kinetic features of the alkylation of acetoacetic ester by 1-chloro-3-methyl-2-butene

1. We studied the effect of the molar ratio of acetoacetic ester (AAE) and 1-chloro-3-methyl-2-butene (PC) on the yield of prenylaeetoacetic ester (I) and diprenylacetoacetic ester (II) and 2-methyl-2-hepten-6-one (MH). With increasing ratio of AAE to PC, the yield of MH increases, the yield of (II) drops, and the yield of (I) remains virtually invariant. 2. We studied the effect of the concentrations of AAE and PC on the molar ratio of (I). (II). and MH in the reaction products and the conversion of PC and showed that ester (I) is an intermediate in the formation of MH and the initial rate of formation of MH depends on the concentrations of AAE and PC to the first power. 3. The kinetic order of the monoalkylation reaction is first order for AAE and PC and the apparent activation energy is -7.95 kcal/mole. These data support an alkylation scheme involving a reversible step of formation of the potassium (or triethylbenzylammonium) derivative of AAE and its alkylation by 1-chloro-3-methyl-2-butene.

The ontogeny of B lymphocytes IV. Induction signals mediating phenotypic conversion of PC.1− to PC.1+B cells

AbstractThe present study presents evidence that spleen and lymph node cell populations contain a distinct subpopulation of B lymphocytes amounting to < 1 % of the total, which are committed and poised to the expression of the PC. 1 alloantigen, and which can be triggered in vitro to express PC.1. The pheno‐type of the PC.l‐inducible cells has been determined as Ig+ Ia+ complement receptor (CR)+ PC.l− which characteristically is associated with mature lymphocytes. Since the PC.l alloantigen identifies plasmacytes, the induction experiments imply that the latter cells are in principle descendents of CR+ B lymphocytes.The induction signal mediating PC.l− to PC.1+ conversion is different from that mediating early pro‐B cell induction. Inducing agents of PC.l−←PC.1 + include carbamylcholine, thymopoietin, prostaglandin F2α and 8‐bromo cyclic GMP, all of which have previously been shown to inhibit early pro‐B cell induction. Conversely, most agents inducing phenotype conversion in early pro‐B cells (e.g. lipopolysaccharide, tumor‐necrotizing serum, isoproterenol, prostaglandin E1 and dibutyryl cyclic AMP) are strong inhibitors of PC. 1 induction. The results suggest that inducible B lymphocytes are under dual control of agents imparting opposing signals to them, but that the mode in which they respond is reversed when they have matured to the CR+ state. Since PC. 1 expression coincides largely with differentiation to antibody‐forming cells, the reversal of responses to regulatory signals may be of significance as a safeguard against spurious activation of B lymphocytes.