The interaction of p62 with RIP links the atypical PKCs to NF-kappaB activation

The two members of the atypical protein kinase C (aPKC) subfamily of isozymes (zetaPKC and lambda/iotaPKC) are involved in the control of nuclear factor kappaB (NF-kappaB) through IKKbeta activation. Here we show that the previously described aPKC-binding protein, p62, selectively interacts with RIP but not with TRAF2 in vitro and in vivo. p62 bridges the aPKCs to RIP, whereas the aPKCs link IKKbeta to p62. In this way, a signaling cascade of interactions is established from the TNF-R1 involving TRADD/RIP/p62/aPKCs/IKKbeta. These observations define a novel pathway for the activation of NF-kappaB involving the aPKCs and p62. Consistent with this model, the expression of a dominant-negative mutant lambda/iotaPKC impairs RIP-stimulated NF-kappaB activation. In addition, the expression of either an N-terminal aPKC-binding domain of p62, or its C-terminal RIP-binding region are sufficient to block NF-kappaB activation. Furthermore, transfection of an antisense construct of p62 severely abrogates NF-kappaB activation. Together, these results demonstrate that the interaction of p62 with RIP serves to link the atypical PKCs to the activation of NF-kappaB by the TNFalpha signaling pathway.

[Asthmatic crisis and spontaneous rupture of the esophagus]

We report a case of spontaneous rupture of oesophagus revealed by a severe asthma attack, in a 78-year-old woman, with continuous dyspneic asthma treated with corticosteroids. We discuss the diagnostic difficulties in spontaneous oesophageal rupture, and emphasize the necessity for always looking for a triggering factor in case of severe attacks of asthma not responding to treatment.

Time-course effects of human recombinant luteinizing hormone on porcine Leydig cell specific differentiated functions

Since recombinant hormones are considered as safer and more reliable in their bioactivity than extractive hormones, the recently available human recombinant luteinizing hormone (r-hLH), will probably replace hCG in the near future, for clinical purposes. This prompted us to investigate whether or not, and by which mechanisms, r-hLH can induce a desensitization of signal transduction and/or an up-regulation of steroidogenic capacity in Leydig cells. The effects of a 30 min to 24 h exposure to r-hLH (10(-9) M) on the differentiated functions of cultured immature porcine Leydig cells were studied by measuring the following parameters: LH/hCG receptor number and mRNA, hCG-, cholera toxin- and forskolin-induced cAMP production, G protein alphas subunit content of the membrane, hCG-, cholera toxin-, forskolin-, 8Br-cAMP-, 22R-OH-cholesterol-, progesterone-, 170H-progesterone-, DHEA-, delta4-androstenedione-induced testosterone secretion and StAR, 3beta-HSD, cytochrome P-450scc and P-450c17 mRNAs. hCG binding sites and LH/hCG receptor mRNA were slowly down regulated by r-hLH, reaching 47+/-1 and 18+/-7% of control at 24 h, respectively. Down-regulation of both hCG- and cholera toxin-induced cAMP production occurred earlier and was more marked, and at 24 h represented only 2.7+/-0.5 and 12.5+/-3.6% of control. Due to the synergistic effect of r-hLH and forskolin on cAMP production, the forskolin-induced cAMP was higher in r-hLH treated than in control cells, but this response also declines with time and was, at 24 h, only 32% of that observed at 30 min. This decreased cAMP production was associated with a less marked decline in the amount of membrane content of Galphas protein. The testosterone production in response to hCG, cholera toxin, forskolin and 8Br-cAMP declined to reach a nadir at 6 h but increased thereafter and at 24 h was significantly higher than in control cells. In contrast, the conversion of several precursors into testosterone remained stable or increased slightly during the first hours of r-hLH treatment and significantly increased at 24 h and this was associated with an increase of StAR, 3beta-HSD, P-450scc and P-450c17 mRNAs. Taken together, the present results indicate that, despite the marked down-regulation of transmembrane signaling, r-hLH increased the steroidogenic capacity of Leydig cells by increasing the expression of several genes encoding the proteins involved in testosterone synthesis.

Enhancement of long-term testosterone secretion and steroidogenic enzyme expression in human Leydig cells by co-culture with human Sertoli cell-enriched preparations

We have shown previously that long-term testosterone secretion, which decreases when human Leydig cells are cultured alone, increases when purified human Leydig and Sertoli cells are cultured together. In this work, human Leydig cell functions were studied further during in vitro culture, either alone or with human Sertoli cells, on a basal membrane derived from bovine corneal endothelial cells. The secretion of testosterone increased during the first week of co-culture and remained elevated up to day 12 of culture. In one prolonged co-culture, testosterone secretion decreased progressively after day 12 and, after 1 month of culture, was at a level similar to that observed during the first 48 h. After culture for 48 h, testosterone secretion in the co-culture was enhanced by 162 +/- 5% (p < 0.0001) compared with values observed when Leydig cells were cultured alone (42.6 +/- 10.6 ng/10(6) Leydig cells/48 h; mean +/- SEM). This change was associated with increase in mRNA levels for 3 beta-hydroxysteroid dehydrogenase delta 5-delta 4-isomerase (2.49 +/- 0.58-fold), cytochrome P450c17 (2.81 +/- 0.99-fold), cytochrome P450scc (5.20 +/- 0.13-fold) and cytochrome P450 aromatase (1.73 +/- 0.21-fold) when Leydig cells were co-cultured with Sertoli cells (p < 0.05 for each enzyme). IGF-I mRNA levels were higher (2.77 +/- 0.72-fold for 7.6 kb and 1.41 +/- 0.07-fold for 1.1-1.3 kb transcripts) in the Leydig-Sertoli cell co-cultures than the sum of the levels in Leydig and in Sertoli cells cultured alone. Both basal and hCG-induced testosterone secretion were enhanced by treatment of the co-culture with human recombinant FSH (50 mIU/mL). For basal testosterone secretion, this increase amounted to 163 +/- 5% compared with Leydig cells cultured alone (p < 0.0001) and by 112 +/- 4% compared with non-FSH treated co-cultures (p < 0.01); for hCG-stimulated testosterone secretion this increase was 220 +/- 12% compared with Leydig cells cultured alone (p < 0.0001) and 132 +/- 8% compared with non-FSH treated co-cultures (p < 0.01). This study confirms the enhancement of long-term testosterone secretion by adult human Leydig cells by co-culture with adult human Sertoli cells and shows that this effect is associated with an enhancement of the expression of several steroidogenic enzymes; it might be mediated, as in other species, through increased production of IGF-I by co-culture.

Localization of atypical protein kinase C isoforms into lysosome-targeted endosomes through interaction with p62

An increasing number of independent studies indicate that the atypical protein kinase C (PKC) isoforms (aPKCs) are critically involved in the control of cell proliferation and survival. The aPKCs are targets of important lipid mediators such as ceramide and the products of the PI 3-kinase. In addition, the aPKCs have been shown to interact with Ras and with two novel proteins, LIP (lambda-interacting protein; a selective activator of lambda/iotaPKC) and the product of par-4 (a gene induced during apoptosis), which is an inhibitor of both lambda/iotaPKC and zetaPKC. LIP and Par-4 interact with the zinc finger domain of the aPKCs where the lipid mediators have been shown to bind. Here we report the identification of p62, a previously described phosphotyrosine-independent p56(lck) SH2-interacting protein, as a molecule that interacts potently with the V1 domain of lambda/iotaPKC and, albeit with lower affinity, with zetaPKC. We also show in this study that ectopically expressed p62 colocalizes perfectly with both lambda/iotaPKC and zetaPKC. Interestingly, the endogenous p62, like the ectopically expressed protein, displays a punctate vesicular pattern and clearly colocalizes with endogenous lambda/iotaPKC and endogenous zetaPKC. P62 colocalizes with Rab7 and partially with lamp-1 and limp-II as well as with the epidermal growth factor (EGF) receptor in activated cells, but not with Rab5 or the transferrin receptor. Of functional relevance, expression of dominant negative lambda/iotaPKC, but not of the wild-type enzyme, severely impairs the endocytic membrane transport of the EGF receptor with no effect on the transferrin receptor. These findings strongly suggest that the aPKCs are anchored by p62 in the lysosome-targeted endosomal compartment, which seems critical for the control of the growth factor receptor trafficking. This is particularly relevant in light of the role played by the aPKCs in mitogenic cell signaling events.

Veratridine-induced depolarization reduces the palmitoylation of brain and myelin glycerolipids

In this study, we have investigated the effect of neuronal depolarization on the palmitoylation of myelin lipids. For this purpose, brain slices from 60-day-old rats were incubated with [3H]palmitate for 1 h in the presence or absence of various drugs. Veratridine (100 microM) reduced the incorporation of [3H]palmitate into all brain glycerolipids by 40-50%, whereas the labeling of sphingolipids was unaffected. Similar results were obtained by using [3H]glycerol as a precursor, demonstrating that veratridine also causes a reduction in the de novo synthesis of glycerolipids. Both tetrodotoxin (1 microM) and ouabain (1 mM) prevented the effect of veratridine, indicating that it is mediated through the opening of voltage-gated sodium channels and involves the stimulation of the Na+/ K+ pump. Decreased levels of both ATP, due to activation of the Na+,K+-ATPase, and the precursor palmitoyl-CoA were found in the veratridine-treated slices, thus explaining the reduction in lipid synthesis. Neuronal depolarization also decreased the synthesis of lipids present in the myelin fraction. The relatively high specific radioactivity of myelin lipids and the results from both repeated purification experiments and mixing experiments ruled out the possibility that the radioactive lipids present in myelin could derive from contamination with other subcellular fraction(s). Because neither mature oligodendrocytes nor myelin is known to express voltage-dependent Na+ channels, it is conceivable that the effect of veratridine on myelin glycerolipid metabolism occurs by an indirect mechanism such as an increase in the extracellular [K+]. However, the presence of 60 mM KCl in the medium did not affect the acylation of either brain or myelin lipids. These results raise questions as to the absence of sodium channels in myelinating oligodendrocytes and/or myelin.

Stimulating effect of both human recombinant inhibin A and activin A on immature porcine Leydig cell functions in vitro

In addition to the regulation of FSH secretion, it has been clearly shown that inhibin and activin have paracrine/autocrine effects in the gonads. We have studied the effect of human recombinant inhibin A and human recombinant activin A on immature porcine Leydig cells in vitro. Leydig cells were prepared by collagenase digestion of testes from 3-week-old piglets, purified on Percoll gradient, then cultured in a chemically defined medium. The cells were treated with increasing amounts of inhibin A or activin A (0.5-200 ng/ml). Direct application of either inhibin A or activin A on Leydig cells for 4 or 48 h did not stimulate basal testosterone secretion. Conversely, treatment of the cells for 48 h with either factor resulted in a dose-dependent increase in hCG-stimulated testosterone secretion (10[-9] M hCG, 2 h) with a maximal effect of 2.40 +/- 0.37- and 2.43 +/- 0.37-fold increases for inhibin A and activin A, respectively, and these changes were associated with a slight increase in LH/hCG-binding sites (1.37 +/- 0.19- and 1.24 +/- 0.11-fold increases). In addition, both inhibin A and activin A enhanced messenger RNA (mRNA) levels of LH/hCG receptor (2.75 +/- 0.40- and 2.53 +/- 0.60-fold increases) and cytochrome P450 17alpha-hydroxylase (6 +/- 1- and 3.5 +/- 0.6-fold increases), but had no effect on side-chain cleavage cytochrome P450 or cytochrome P450 aromatase mRNAs. 3beta-Hydroxysteroid dehydrogenase mRNA levels were increased (3.1 +/- 1.3-fold increase) by activin A, but not by inhibin A. However, inhibin A blocked the stimulatory action of activin A. In keeping with these changes in the steroidogenic enzyme mRNAs, both peptides enhanced the conversion of exogenous 22R-hydroxycholesterol and progesterone, but only activin A increased the conversion of dehydroepiandrosterone into testosterone. In conclusion, our findings demonstrate that both inhibin A and activin A have a stimulatory effect on immature porcine Leydig cell differentiated function in vitro. As inhibin has a stimulatory and activin has an inhibitory effect on rat Leydig cell function in vitro, the effects of these factors on Leydig cells seem to be species dependent.

Syphilis serology in human immunodeficiency virus infection: evidence for false-negative fluorescent treponemal testing

Injection drug users were assessed serologically for human immunodeficiency virus infection and syphilis every 6 months. Treatment histories were reviewed for any high-titer biologic false-positive (BFP) reactors, that is, persons with rapid plasma reagin (RPR) titers > or = 1:4 and negative results for fluorescent treponemal antibody absorption (FTA-ABS) tests. Selected sera were analyzed further by immunoblotting for the presence of antibodies reactive with specific Treponema pallidum antigens. Of 112 BFP reactors, 35 (31%) had at least one RPR test reactive at a dilution >1:8 while the FTA-ABS test remained nonreactive. Five reactors (4.5%) converted from nonreactive to reactive by FTA-ABS test; 4 (3.6%) were reactive by FTA-ABS tests but later became nonreactive. Antibodies to T. pallidum membrane antigens were detected in some samples that were persistently nonreactive by FTA-ABS test. Serologic patterns over time, along with very high-titer BFP reactions and reactivity with T. pallidum-specific antigens, suggest that some BFP reactions may represent FTA-negative syphilis.

T cell tolerance to kappa light chain (L kappa): identification of a naturally processed self-C kappa-peptidic region by specific CD4+ T cell hybridomas obtained in L kappa-deficient mice

In contrast to H-2d kappa light chain-deficient mice (kappa-/-), BALB/c (kappa+/+) mice fail to respond to kappa light chains (L kappa). This suggests that C kappa-specific T cells are tolerant to this self-antigen in kappa+/+ mice. To get insights into the cellular and molecular basis of this tolerance, we first characterized the presented L kappa-derived C kappa-peptidic region(s). Among a library of overlapping peptides spanning the whole C kappa sequence, only three consecutive peptides are recognized by CD4+ T cell hybridomas obtained in L kappa-immunized kappa-/- mice. This C kappa-peptidic region, which is also the only one containing the I-Ed-binding consensus motif, is immunogenic since it is able to prime lymph node cells of kappa-/- mice to subsequent in vitro proliferative response to either L kappa or kappa+/+ APC. Conversely, no kappa+/+ T cell proliferation is observed under the same conditions. Activation of our hybridomas by cells from central and peripheral lymphoid tissues reveals that this C kappa region is naturally expressed on BALB/c kappa+/+ APC. In addition to B cells, macrophages and dendritic cells are able to present this region. Taken together our data suggest that the described self-C kappa region is implicated in the C kappa-specific CD4+ T cell tolerization in BALB/c mice.

Today's CIO: catalyst for managed care change

As the impact of managed care increases and capitation becomes all pervasive, healthcare providers' attention to cost control will intensify. For integrated delivery networks (IDNs) to be competitive, today's CIO must leverage managed care as a catalyst for change, and use a sophisticated information system toolset as the means to an integrated end. An area many CIOs target for fast results and maximum cost savings in resource management. This article reviews how Dick Escue, chief information officer at Baptist Memorial Health Care Corporation (Memphis, TN), uses electronic information management systems to integrate and conserve the resources of Baptist's widespread healthcare organization.

[Physiopathology of closed thoracic trauma]

Any thoracic trauma causes more or less severe hypoxia, due to pain, pleural effusion, mechanical ventilation disorders and pulmonary contusion. These four factors lead to bronchial congestion, which in turn aggravates hypoxia. More or less rapidly a vicious circle of respiratory failure is created. It can be broken only by early treatment of the cause. Without such treatment, respiratory failure quickly becomes autonomic and treatment of the cause is no longer sufficient.

Does positive selection determine the B cell repertoire?

To know whether each newly formed B cell has an equal chance of survival in the organism, we analyzed the composition of the B cell repertoire of extremely limited diversity by generating mu-transgenic kappa-knockout mice. Surprisingly, in both types of mice studied, the B cell repertoire is mainly composed of cells expressing the mu-transgene-encoded chain associated with only one out four available lambda types depending on the mu transgene. Moreover, B cell differentiation cultures in vitro show that newly formed B cells can express the various lambda types regardless of the presence or absence of the mu transgenes. These results show a drastic impact of the heavy chain on the lambda light chain repertoire expressed in the periphery. The overexpression of a unique heavy/light chain pairing therefore results from selective processes. The immature B cells may be positively selected to provide the immunocompetent B cells in the periphery.

The product of par-4, a gene induced during apoptosis, interacts selectively with the atypical isoforms of protein kinase C

The atypical PKCs are involved in a number of important cellular functions, including cell proliferation. We report here that the product of the par-4 gene specifically interacts with the regulatory domains of zeta PKC and lambda/LPKC, which dramatically inhibits their enzymatic activity. This is particularly challenging, because expression of par-4 has been shown to correlate with growth inhibition and apoptosis. Results are shown here demonstrating that the expression of par-4 in NIH-3T3 cells induces morphological changes typical of apoptosis, which are abrogated by cotransfection of either wild-type zeta PKC or lambda/LPKC, but not by their respective kinase-inactive mutants. These findings support a role for the atypical PKC subspecies in the control of cell growth and survival.

Regulation by gonadotropins of the messenger ribonucleic acid for P450 side-chain cleavage, P450(17) alpha-hydroxylase/C17,20-lyase, and 3 beta-hydroxysteroid dehydrogenase in cultured pig Leydig cells

The Leydig cell from the immature pig provides a good model for studying testicular steroidogenesis. Regulation of the enzymes involved, which has been well studied in rodents, has not been characterized in the pig. The objectives of this study were to examine the regulation of three steroidogenic enzymes in pig Leydig cells by LH/hCG and testosterone. The mRNA for P450 side-chain cleavage and P450(17) alpha-hydroxylase/C17-20-lyase, although constitutively expressed, decreased over time in culture, while that for 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) remained relatively constant. The mRNA for all three enzymes was increased in a dose- and time-dependent manner by treatment with hCG. Run-on experiments demonstrated that the main effect of the hormone was at the level of transcription. Treatment with hydroxyflutamide, either alone or in combination with hCG, had no effect on the mRNA for these enzymes. Treatment with hCG plus aminoglutethimide, an inhibitor of steroidogenesis, had no effect on the mRNA for the two P450 enzymes, but resulted in an increase in mRNA for 3 beta HSD when compared to treatment with hCG alone. However, exogenous testosterone could not block the effect of aminoglutethimide. Therefore, the steroidal regulation of 3 beta HSD in pig Leydig cells may act through a mechanism separate from the androgen receptor. While aspects of the regulation of these enzymes are similar to those seen in rodents, some significant differences exist. Our results support the concept that regulation of steroidogenic enzymes in Leydig cells is species-specific.

Mediastinal mass following chemotherapy in patients with Ewing sarcoma and osteosarcoma

Thymic hyperplasia following combination chemotherapy for malignant disease is very uncommon in adolescents and adults. Our experience includes a thymic enlargement noted on the sequential computed tomography (CT) in three patients who were disease-free after chemotherapy for Ewing sarcoma (2) and osteosarcoma (1). The development of an anterior mediastinal mass after successful chemotherapy does not always imply relapse of malignant disease. To prevent inappropriate treatment, the possibility of benign aetiology must be considered.

Acute liver failure due to diffuse intrasinusoidal metastases of urothelial carcinoma

We report one case of urothelial carcinoma with diffuse intrasinusoidal metastasis to the liver and clinical presentation mimicking fulminant hepatic failure. The patient was a 69-year-old man admitted to the hospital for upper gastrointestinal hemorrhage. Two years previously he had undergone a right nephrectomy for urothelial carcinoma (T2, GII). After five days of hospital admission, he developed progressive jaundice, ascites, deteriorating mental status with high serum enzyme activities (AST, ALT, LDH, alkaline phosphatase) and death 20 days after hospitalization. No grossly detectable hepatic metastatic nodules were demonstrated. A percutaneous postmortem liver biopsy revealed a diffuse infiltration of tumor cells into the hepatic sinusoids and venous invasion.

The lambda B cell repertoire of kappa-deficient mice

Analysis of the B cell repertoire is complicated by the huge diversity inherent in the germ line determined combinatory. Making use of knockout technology, kappa-deficient mice have been obtained. They constitute a shrewd model to follow the expression of an Ig minilocus, such as the lambda one, in the normal condition compared with classical transgenic models. Indeed, in contrast to wild type mice, in which only 5% of lambda B cells are produced, these mutant mice exclusively produce lambda positive B cells. Although, the lambda locus is well characterized and has a relatively simple organization, the mechanistic and selective pressures that govern its utilization are still poorly understood. The analysis of the lambda B cell repertoire in kappa-deficient mice, should therefore bring more conclusive informations. Here we present the lambda subtype distribution in the various cellular compartments of the kappa-deficient mice, and discuss the rules that can be responsible for this distribution. Our recent data indicate that the lambda subtype proportions in the bone marrow and the spleen result, for the major part, from mechanistic processes (i.e., recombinase accessibility, production of V-J functional joint and H/L pairings) while the lambda proportions found in the peritoneal cavity ensue from selective processes. Finally, the capacity to respond to various antigens is discussed from such a generated lambda B cell repertoire.

Lambda-interacting protein, a novel protein that specifically interacts with the zinc finger domain of the atypical protein kinase C isotype lambda/iota and stimulates its kinase activity in vitro and in vivo

The members of the atypical subfamily of protein kinase C (PKC) show dramatic structural and functional differences from other PKC isotypes. Thus, in contrast to the classical or novel PKCs, they are not activated by diacylglycerol or phorbol esters. However, the atypical PKCs are the target of important lipid second messengers such as ceramide, phosphatidic acid, and 3'-phosphoinositides. The catalytic and pseudosubstrate sequences in the two atypical PKCs (lambda/iota PKC and zeta PKC) are identical but are significantly different from those of conventional or novel PKCs. It has been shown that microinjection of a peptide with the sequence of the pseudosubstrate of the atypical PKC isotypes but not of alpha PKC or epsilon PKC dramatically inhibited maturation and NF-kappa B activation in Xenopus oocytes, as well as reinitiation of DNA synthesis in quiescent mouse fibroblasts. This indicates that either or both atypical isoforms are important in cell signalling. Besides the pseudosubstrate, the major differences in the sequence between lambda/iota PKC and zeta PKC are located in the regulatory domain. Therefore, any functional divergence between the two types of atypical PKCs will presumably reside in that region. We report here the molecular characterization of lambda-interacting protein (LIP), a novel protein that specifically interacts with the zinc finger of lambda/iota PKC but not zeta PKC. We show in this paper that this interaction is detected not only in vitro but also in vivo, that LIP activates lambda/iota PKC but not zeta PKC in vitro and in vivo, and that this interaction is functionally relevant. Thus, expression of LIP leads to the transactivation of a kappa B-dependent promoter in a manner that is dependent on lambda/iota PKC. To our knowledge, this is the first report on the cloning and characterization of a protein activator of a PKC that binds to the zinc finger domain, which has so far been considered a site for binding of lipid modulators. The fact that LIP binds to lambda/iota PKC but not to the highly related zeta PKC isoform suggests that the specificity of the activation of the members of the different PKC subfamilies will most probably be accounted for by proteins like LIP rather than by lipid activators.

Emergence in C kappa knockout mice of a diverse cytotoxic T lymphocyte repertoire that recognizes a single peptide from the immunoglobulin constant kappa light chain region

Allotype- or idiotype-specific CD4+ T cells have been reported to recognize immunoglobulin (Ig) peptides presented by class II molecules. In contrast, few data are available concerning the generation of Ig peptide-specific CD8+ T cells. We have therefore investigated whether T-depleted spleen cells from Ig kappa light chain-expressing 129/Sv mice (129 kappa +/+) could induce, in C kappa knockout mice (129 kappa -/-), the generation of Ig constant kappa light chain region (C kappa)-specific cytotoxic T lymphocytes (CTL). The determination of TCR beta chain expressed by nine CTL clones, together with the use of a library of overlapping peptides spanning the whole C kappa sequence, show that the B cells from kappa +/+ mice are able to elicit in C kappa knockout mice, the emergence of a diverse CTL repertoire that recognizes one single C kappa peptide presented by the H-2Kb class I molecule. In addition, these data support the notion that B cells are able to process and present on their class I molecules, peptides generated from their own kappa light chains.

Biochemically active sesquiterpene lactones from Ratibida mexicana

Bioactivity-directed fractionation of the methanol extract of the roots of Ratibida mexicana resulted in the isolation of two bioactive sesquiterpene lactones, isoalloalantolactone and elema-1,3,11-trien-8,12-olide. Both compounds caused a significant inhibition of the radicle growth of Amaranthus hypochondriacus and Echinochloa crus-galli, exerted moderate cytotoxic activity against three different solid tumour cell lines and inhibited significantly the radial growth of three phytopathogenic fungi. Isoalloalantolactone also caused the inhibition of ATP synthesis, proton uptake and electron transport (basal, phosphorylating and uncoupled) from water to methylviologen, therefore acting as a Hill's reaction inhibitor. The lactone did not affect photosystem I but inhibited photosystem II. The site of inhibition of isoalloalantolactone is located in the span of P680 to QA redox enzymes because the uncoupled electron transport from water to silicomolybdate and, from DPC to DCIP are inhibited approximately to the same extent.