MATH/BTB CRL3 receptors target the homeodomain-leucine zipper ATHB6 to modulate abscisic acid signaling

Being sessile organisms, plants need rapid and finely tuned signaling pathways to adapt their growth and survival over their immediate and often adverse environment. Abscisic acid (ABA) is a plant hormone crucial for both biotic and abiotic stress responses. In this study, we highlight a function of six Arabidopsis MATH-BTB proteins in ABA signaling. MATH-BTB proteins act as substrate-binding adaptors for the Cullin3-based ubiquitin E3 ligase. Our genetic and biochemical experiments demonstrate that the MATH-BTB proteins directly interact with and target for proteasomal degradation the class I homeobox-leucine zipper (HD-ZIP) transcription factor ATHB6, which was previously identified as a negative regulator of ABA responses. Reducing CUL3(BPM) function leads to higher ATHB6 protein accumulation, reducing plant growth and fertility, and affects stomatal behavior and responses to ABA. We further demonstrate that ABA negatively regulates ATHB6 protein turnover, a situation reminiscent to ABI5, another transcription factor involved in ABA signaling.

Development of an optimized procedure for the preparation of rat intestinal microsomes: comparison of hepatic and intestinal microsomal cytochrome P450 enzyme activities in two rat strains

The objective of this study was to characterize cytochrome P450 (CYP) activities in both intestinal and hepatic microsomes from Wistar and Sprague-Dawley rats. Specific probes for measuring CYP activities were selected using rat recombinant CYP. The intestinal microsome preparation was optimized getting a more relevant and reproducible abundance of CYPs to measure CYP activities. Testosterone, propranolol, diclofenac, and midazolam were determined as specific substrates of rat CYP2C11, CYP2D2, CYP2C6, and CYP3A, respectively. Ethoxyresorufin and pentoxyresorufin were not specific substrates of CYP1A2 and CYP2B1, respectively. Hepatic and intestinal microsomes expressed active CYP1A1, CYP1A2, CYP2B1, and CYP3A2. Only liver expressed active CYP2C6, CYP2C11, and CYP2D2. Wistar liver expressed more active CYP1A and CYP3A2, but less active CYP2B1 than Wistar intestine. Sprague-Dawley liver expressed more active CYP2B1 and CYP3A2, but less active CYP1A than Sprague-Dawley intestine. In conclusion, CYP activities were qualitatively equivalent but not quantitatively in both strains.

Liquid Chromatography-Accurate Radioisotope Counting and Microplate Scintillation Counter Technologies in Drug Metabolism Studies

The present study involves an analysis of the performance of liquid chromatography (LC)-accurate radioisotope counting (ARC) and microplate scintillation counter (TopCount) technologies in drug metabolism studies. For the purpose of evaluating these systems, biological samples resulting from the metabolism of a radiolabeled [14C] compound, known as compound B, are analyzed using LC-ARC and TopCount under similar high-performance LC conditions. Counting efficiency is 83% for LC-ARC, 77% for TopCount, and linearity is R2 of 0.9998 versus 0.9984, respectively. The limit of detection for LC-ARC is 12 disintegrations per minute (dpm) with 1-min/fraction counting, yet for TopCount it is 8.7 dpm with 5-min/fraction counting. Under optimal conditions for each, the total run time of LC-ARC is approximately half that of TopCount. These results indicate that there is no significant difference between these two systems in terms of efficiency, linearity, and limit of detection. However, the LC-ARC system does not involve any manual operations, yet TopCount requires manual sample transfer and data import. This study shows that impressive progress has been made in the technology of radioisotope counting in drug metabolism using LC-ARC. This system enhances the resolution of radiochromatograms and is able to measure volatile metabolites that TopCount cannot detect at all. The ability to acquire mass spectra online is also a major advancement. The overall results suggest that the combination of LC-ARC with radioactivity detection and mass spectrometry has great potential as a powerful tool for radioisotope measurement in metabolite identification studies during drug discovery and development.

National survey on cholecystectomy related bile duct injury--public health and financial aspects in Belgian hospitals--1997

Public health and financial aspects of cholecystectomy related bile duct injury (BDI) are highlighted in a National Cholecystectomy Survey carried out through 'datamining' the Federal State Medical Records Summaries and Financial Summaries of all Belgian hospitals in 1997. All cancer diagnoses, children < or = 10 years, cholecystectomies performed as an abdominal co-procedure or patients having undergone other non-related surgery were excluded from the study. 10.595 laparoscopic (LC) and 1.033 open cholecystectomies (OC) as well as 137 secondary BDI treatments (LC/OC) were included in the survey (total 11.765). Both LC and OC groups turned out to be significantly different as to distribution of patient's age and APR-DRG severity classes. Composite criteria in terms of ICD-9-CM and billing codes were elaborated to classify: 1) primary, intra-operatively detected and treated BDI (N = 30), 2) primary delayed BDI treatments (N = 38), 3) secondary BDI treatments (N = 137), 4) non-BDI abdomino-surgical complications (N = 119), 4) uneventful laparoscopic (N = 7.476) and 5) uneventful open cholecystectomy (N = 681). Complication rates, community costs of LC and OC groups, incidence of preoperative ERCP and/or intra-operative cholangiography as well as interventions for complications were studied. Incidence of cholecystectomy related BDI was 0.37% in LC, 2.81% in OC and 0.58% overall. Average costs amounted to [symbol: see text] 1.721 for uneventful LC, [symbol: see text] 2.924 for uneventful OC, [symbol: see text] 7.250 for primary, intra-operatively detected and immediately treated BDI [symbol: see text] 9.258 for primary delayed BDI treatments, [symbol: see text] 6.076 for secondary BDI treatments and [symbol: see text] 10.363 for non-BDI abdomino-surgical complications. In conclusion BDI with cholecystectomy reveals to be a serious complication increasing the overall average cost factor ninefold if not detected intra-operatively, in which case the raise is only fourfold. As a consequence BDI should be avoided by all means. In this respect 4 crucial surgical guidelines are emphasised.

Sub-cellular localisation of GFP-tagged tobacco mitotic cyclins during the cell cycle and after spindle checkpoint activation

We have previously shown that the tobacco cyclin B1;1 protein accumulates during the G2 phase of the cell cycle and is subsequently destroyed during mitosis. Here, we investigated the sub-cellular localisation of two different B1-types and one A3-type cyclin during the cell cycle by using confocal imaging and differential interference contrast (DIC) microscopy. The cyclins were visualised as GFP-tagged fusion proteins in living tobacco cells. Both B1-type cyclins were found in the cytoplasm and in the nucleus during G2 but when cells entered into prophase, both cyclins became associated with condensing chromatin and remained on chromosomes until metaphase. As cells exited metaphase, the B1-type cyclins became degraded, as shown by time-lapse images. A stable variant of cyclin B1;1-GFP fusion protein, in which the destruction box had been mutated, maintained its association with the nuclear material at later phases of mitosis such as anaphase and telophase. Furthermore, we demonstrated that cyclin B1;1 protein is stabilised in metaphase-arrested cells after microtubule destabilising drug treatments. In contrast to the B1-type cyclins, the cyclin A3;1 was found exclusively in the nucleus in interphase cells and disappeared earlier than the cyclin B1 proteins during mitosis.

Effects of the polyubiquitin gene Ubi. U4 leader intron and first ubiquitin monomer on reporter gene expression in Nicotiana tabacum

We have previously shown by RNA gel blot analyses that the tobacco polyubiquitin-encoding gene Ubi.U4 is expressed in a complex pattern during plant development (Genschik et al., 1994). In order to study its tissue-specific expression, we cloned the fragment containing the -263 bp proximal promoter of the gene, the leader intron and the first ubiquitin monomer in front of the reporter GUS gene. Histochemical analyses for GUS activity during tobacco plant development revealed that the gene is expressed at variable amounts in many plant tissues with high levels in metabolically active and/or dividing cells and in the vascular tissues of the plant. We also analysed the expression pattern of constructs in which either the intron or the intron together with the first ubiquitin monomer were deleted. Our results indicate that the ubiquitin leader intron is not only a quantitative determinant of gene expression but may also influence the tissue-specific expression pattern.

Cell cycle-dependent proteolysis and ectopic overexpression of cyclin B1 in tobacco BY2 cells

Activation of cyclin B/Cdc2 kinase complex triggers entry into mitosis in all eukaryotic cells. Although cyclin gene expression has been extensively studied in plants, not much is known at the level of the protein stability and function. Here, we demonstrated by using the highly synchronizable tobacco BY2 cell culture, that endogenous cyclin B1 protein undergoes cell cycle-dependent proteolysis and is stabilized when the spindle checkpoint has been activated. Furthermore, we established transgenic tobacco BY2 cell cultures expressing under the control of an inducible promoter, cyclin B1 protein as well as its non-degradable form as fusion proteins with GFP and found that the ectopic expression of these proteins did not dramatically disturb the cell cycle progression. These results indicate that, to a certain extent, cell cycle exit is possible without cyclin B1 proteolysis.

Cell cycle -dependent proteolysis in plants. Identification Of the destruction box pathway and metaphase arrest produced by the proteasome inhibitor mg132

It is widely assumed that mitotic cyclins are rapidly degraded during anaphase, leading to the inactivation of the cell cycle-dependent protein kinase Cdc2 and allowing exit from mitosis. The proteolysis of mitotic cyclins is ubiquitin/26S proteasome mediated and requires the presence of the destruction box motif at the N terminus of the proteins. As a first attempt to study cyclin proteolysis during the plant cell cycle, we investigated the stability of fusion proteins in which the N-terminal domains of an A-type and a B-type tobacco mitotic cyclin were fused in frame with the chloramphenicol acetyltransferase (CAT ) reporter gene and constitutively expressed in transformed tobacco BY2 cells. For both cyclin types, the N-terminal domains led the chimeric cyclin-CAT fusion proteins to oscillate in a cell cycle-specific manner. Mutations within the destruction box abolished cell cycle-specific proteolysis. Although both fusion proteins were degraded after metaphase, cyclin A-CAT proteolysis was turned off during S phase, whereas that of cyclin B-CAT was turned off only during the late G2 phase. Thus, we demonstrated that mitotic cyclins in plants are subjected to post-translational control (e.g., proteolysis). Moreover, we showed that the proteasome inhibitor MG132 blocks BY2 cells during metaphase in a reversible way. During this mitotic arrest, both cyclin-CAT fusion proteins remained stable.

A YAC contig map of Arabidopsis thaliana chromosome 3

We have constructed a YAC contig map of Arabidopsis thaliana chromosome 3. From an estimated total size of 25 Mb, about 21 Mb were covered by 148 clones arranged into nine YAC contigs, which represented most of the low-copy regions of the chromosome. YAC clones were anchored with 259 molecular markers, including 111 for which linkage information was previously available. Most of the genetic map was included in the YAC coverage, and more than 60% of the genetic markers from the reference recombinant inbred line map were anchored, giving a high level of integration between the genetic and physical maps. The submetacentric structure of the chromosome was confirmed by physical data; 3R (the top arm of the linkage map) was about 12 Mb, and 3L (the bottom arm of the linkage map) was about 9 Mb. This YAC physical map will aid in chromosome walking experiments and provide a framework for large-scale DNA sequencing of chromosome 3.

The 20S proteasome gene family in Arabidopsis thaliana

The complexity of the proteasome gene family in higher plants was investigated by identification and sequencing cDNA clones from the Arabidopsis thaliana database showing homologies to 20S proteasome subunits. We identified plant counterparts for each of the 14 proteasomal subunit subfamilies. Moreover, several of them were highly related isoforms. Mapping data indicate a random distribution of the proteasome genes over the Arabidopsis genome.

Characterization of a tobacco extensin gene and regulation of its gene family in healthy plants and under various stress conditions

A genomic clone (Ext 1.4) encoding an extensin was isolated from a Nicotiana tabacum genomic library. The encoded polypeptide showed features characteristic of extensins such as Ser-(Pro)4 repeats and a high content in Tyr and Lys residues. The presence of one Tyr-Leu-Tyr-Lys motif suggests the possibility for one intramolecular isodityrosine cross-link whereas numerous Val-Tyr-Lys motifs may participate in intermolecular cross-links. This extensin appears to be close to an extensin already characterized in N. tabacum but very different from the Ext 1.2 extensin of N. sylvestris. The analysis of genomic DNA gel blots using probes spanning different parts of the gene showed that the Ext 1.4 gene belongs to a complex multigene family having one member originating from N. sylvestris and three members from N. tomentosiformis. The Ext 1.4 specific probe found a 1.4 kb mRNA in stems, roots, ovaries and germinating seeds of healthy plants. The Ext 1.4 gene family is strongly induced in actively dividing cell suspension cultures and after wounding of leaves or stems in conditions where root formation occurs. On the contrary, it is not induced in leaves in response to a hypersensitive reaction to a viral infection or after elicitor treatment.

Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs

Nearly 7000 Arabidopsis thaliana-expressed sequence tags (ESTs) from 10 cDNA libraries have been sequenced, of which almost 5000 non-redundant tags have been submitted to the EMBL data bank. The quality of the cDNA libraries used is analysed. Similarity searches in international protein data banks have allowed the detection of significant similarities to a wide range of proteins from many organisms. Alignment with ESTs from the rice systematic sequencing project has allowed the detection of amino acid motifs which are conserved between the two organisms, thus identifying tags to genes encoding highly conserved proteins. These genes are candidates for a common framework in genome mapping projects in different plants.

A novel wound-inducible extensin gene is expressed early in newly isolated protoplasts of Nicotiana sylvestris

A cDNA clone (6PExt 1.2) encoding a novel extensin was isolated from a cDNA library made from 6 h old mesophyll protoplasts of Nicotiana sylvestris. The screening was performed with a heterologous probe from carrot. The encoded polypeptide showed features characteristic of hydroxyproline-rich glycoproteins such as Ser-(Pro)4 repeats and a high content in Tyr and Lys residues. The presence of four Tyr-X-Tyr-Lys motifs suggests the possibility for intramolecular isodityrosine cross-links whereas three Val-Tyr-Lys motifs may participate in intermolecular cross-links. The analysis of genomic DNA gel blots using both the N. sylvestris and the carrot clones as probes showed that the 6PExt 1.2 gene belongs to a complex multigene family encoding extensin and extensin-related polypeptides in N. sylvestris as well as in related Nicotianeae including a laboratory hybrid. This was confirmed by the analysis of RNA gel blots: a set of mRNAs ranging in size from 0.3 kb to 3.5 kb was found by the carrot extensin probe. The 6PExt 1.2 probe found a 1.2 kb mRNA in protoplasts and in wounded tissues as well as a 0.9 kb mRNA which seemed to be stem-specific. The gene encoding 6PExt 1.2 was induced by wounding in protoplasts, in leaf strips and after Agrobacterium tumefaciens infection of stems.

Molecular characterization of a beta-type proteasome subunit from Arabidopsis thaliana co-expressed at a high level with an alpha-type proteasome subunit early in the cell cycle

Proteasomes are the essential components of complexes involved in an extralysosomal energy- and ubiquitin-dependent proteolytic pathway. The first alpha-type proteasome subunit in plants has recently been described. In this work, the sequence of the first beta-type proteasome subunit in plants, isolated from Arabidopsis thaliana cDNA libraries is reported. The mRNA accumulation of both subunits was analysed and compared with those of the ubiquitin and histone mRNAs, in different tissues and during re-initiation of mitotic activity. It is demonstrated that in plants, as in animal cells, the transcripts of both the alpha-type and beta-type proteasome subunits accumulate to high levels during cell proliferation, in parallel with mRNAs coding for a ubiquitin fusion protein and several polyubiquitins, but earlier than those coding for histone H4 whose expression is known to be coupled to DNA synthesis. These results suggest that, as in animal cells, proteasomes may be involved in the progression of the cell cycle.

Why are quiescent mesophyll protoplasts from Nicotiana sylvestris able to re-enter into the cell cycle and re-initiate a mitotic activity?

Mesophyll protoplasts of Nicotiana sylvestris incubated in an adequate culture medium re-enter very rapidly into the cell cycle and divide. The transition G0/G1 is accompanied by a complete reversion of the program of gene expression. The program of the photosynthetic differentiated mesophyll cell is abolished whereas a new multipartite program of a highly stressed but ready-to-divide cell is established. Some genes encode proteins which structure suggests they may play key roles in these events. Most of the induced genes are under multiple controls: stress and/or development. Stress response and cellular re-organization might thus be closely related events that cannot be dissociated. It is probable that the re-entry of a protoplast into the cell cycle, ie the initial step of totipotency, closely depends on the coordinated activation of a set of genes that share common regulatory mechanisms.

Ubiquitin genes are differentially regulated in protoplast-derived cultures of Nicotiana sylvestris and in response to various stresses

Four ubiquitin mRNA size classes were found to be differentially regulated in mesophyll protoplast-derived cultures of Nicotiana sylvestris. Three mRNA families of 1.9, 1.6 and 1.35 kb were expressed as soon as protoplasts were isolated. The 1.9 and 1.6 kb size classes were transiently expressed during the first hours of culture, whereas the level of expression of the 1.35 kb size class was maintained as long as cells kept dividing. A 0.7 kb mRNA size class started to be expressed just before the first divisions were observed. cDNAs corresponding to each of these families were isolated from a 6-h-old protoplast cDNA library and characterized. The 1.9, 1.6 and 1.35 kb mRNAs thus encode 7- or more, 6- and 5-mers, respectively, of ubiquitin whereas the 0.7 kb mRNAs encode a monomer of ubiquitin fused to a carboxyl extension protein of 52 amino acids. The expression of ubiquitin genes was studied, using probes specific for each of these transcript families, during protoplast culture and, for comparison, after various stresses including heat shock, HgCl2 treatment, a viral infection giving rise to a hypersensitive reaction, and an Agrobacterium tumefaciens infection which resulted in tumour formation. The 1.9 and 1.6 kb mRNA size classes were found to be stress-regulated, the 0.7 kb mRNA size class developmentally regulated and the 1.35 kb size class both stress- and developmentally regulated.

Isolation and characterization of a cDNA encoding a 3-hydroxy-3-methylglutaryl coenzyme A reductase from Nicotiana sylvestris

A cDNA library from freshly isolated mesophyll protoplasts of Nicotiana sylvestris was differentially screened using cDNAs from leaves, leaf strips submitted to the same stress as protoplasts during the isolation procedure, and cell suspension cultures. One of the selected clones (6P2) was found to encode a putative polypeptide highly homologous to previously characterized 3-hydroxy-3-methylglutaryl coenzyme A reductases. The C-terminal region of the polypeptide was highly conserved whereas its N-terminal region including the trans-membrane domains and the linker was more variable. Apart from protoplasts, the 6P2 gene was found to be expressed in apexes, anthers, roots, and in stressed leaf strips after 24 h of culture, during the hypersensitive reaction to viral infection and after HgCl2 treatment. This pattern of expression is consistent with a role in plant defence mechanisms.

Characterization of genes expressed in mesophyll protoplasts of Nicotiana sylvestris before the re-initiation of the DNA replicational activity

To decipher the early events preceding the re-entry of somatic cells into the cell cycle, we constructed a cDNA library from 6-h-old protoplasts of Nicotiana sylvestris. We characterized three mRNAs, via their cDNAs, that accumulate at very high levels 6 h after the beginning of the culture. Two of them could be identified by comparison of the deduced amino acid sequence to databanks. 6P10 is a novel type I trypsin inhibitor, which has the peculiarity of being devoid of the pro-sequence peptide described to be essential for transport to the vacuole. 6P73 is a novel, moderately anionic peroxidase. 6P50 belongs to a gene family not yet identified. These genes are highly expressed in protoplasts at the beginning of the culture and moderately in roots, but are neither expressed in response to chemical treatment, heat shock, pathogen attacks nor during tumor induction. These findings suggest that the activation of these genes corresponds not only to a specific adaptation of protoplasts to the new environment but also, since their level of expression decreases at the onset of division, to a sequence of events connected with the establishment of the new program of gene expression of the dividing cell.

Isolation and characterization of a plant cDNA showing homology to animal glutathione peroxidases

A cDNA library from freshly isolated protoplasts was differentially screened using cDNAs from mesophyll cells, stressed leaf strips and cell suspension cultures. One of the selected clones, 6P229, turned out to encode a putative polypeptide showing homology to the btuE periplasmic protein of Escherichia coli and to animal selenium-dependent glutathione peroxidases. A major difference was that the putative selenocysteine in the active site was not encoded by the termination codon TGA. The 6P229 gene was found to be expressed in germinating seeds, in apex and in flowers, as well as in stressed tissues. This pattern of expression would be consistent with a key role in cellular metabolism such as defense against oxidative stresses.

Genes encoding the small subunit of RUBISCO belong to two highly conserved subfamilies in Nicotianeae

The sequences of seven complementary DNAs or genes encoding the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO) in several Nicotianeae were examined. Two new SSU genes isolated from Nicotiana sylvestris were included. Both sequence comparisons and Southern analyses with specific probes reveal that SSU genes fall into two homogeneous subfamilies that are highly conserved in Nicotianeae and are also present in other Solanaceae. Additional criteria such as number of introns and level of expression fitted to this classification. Homogeneity must have been maintained by gene conversion and/or an unusually high fidelity of DNA replication, whereas traces of slippage-stranded DNA mispairing and/or transposition probably explain local changes. Taken as a whole, these results show that the divergence between the two subfamilies predated the divergence between genera inside the Solanaceae, but that Nicotianeae retained the most simple SSU gene family structure.

Is ubiquitin involved in the dedifferentiation of higher plant cells?

Transformation of a mesophyll cell into a viable protoplast that is able to re-enter the cell cycle, divide and further differentiate into organs, is accompanied by a very rapid and important increase in ubiquitin gene expression. Three major size classes of ubiquitin mRNA transcripts were observed in protoplasts as soon as they were isolated and incubated in their culture medium. The 1.6 kb mRNAs were expressed in response to the stress caused by the isolation procedure. They decreased after a few hours of incubation in the culture medium. The 1.9 kb and the 1.3 kb mRNAs enhanced in protoplasts were also observed in young leaves and in actively dividing cells: they appeared to be developmental-stage specific. They are not expressed in response to the stress, but may be considered to be part of the dedifferentiation program induced in protoplasts. These results suggest, as the enhancement of ubiquitin gene expression coincides with the dramatic changes in gene expression observed in protoplasts, that ubiquitin may play a fundamental role in the process of cellular dedifferentiation.

Serum unsaturated vitamin B12 proteins in adult patients with sickle cell anaemia (HbSS)

The unsaturated vitamin B12 binding capacity (UBBC) of serum, the three transcobalamins (TC I, TC II, TC III) and serum cobalamin have been studied in adult sickle cell patients with Hb SS. An increase in the level of the binding capacities of TC I and TC III resulting in an increase in UBBC was observed in these patients. There was no difference in the level of the binding capacity of TC II, while there was a significant reduction in the level of serum cobalamin. These changes in the pattern of these binding proteins are discussed in relation to the changes of these binding proteins in paediatric sickle cell patients with Hb SS. The results indicate that the pattern of these binding proteins changes with age among sickle cell patients resulting in an increased level of the binding capacities of TC I and TC III. These increases lend support to the view that these two similar binding proteins are involved in the defence mechanism of the body.

Correlation between serum enzymes and serum unsaturated vitamin B12 binding proteins in primary liver carcinoma

The serum unsaturated vitamin B12-binding capacity (UBBC), unsaturated transcobalamin (UTC) I, UTC II, UTC III levels, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase activities and bilirubin concentration were estimated in 61 patients with liver diseases (31 with hepatoma, 30 with viral hepatitis). The levels of serum cobalamin, UTC I, UTC III, UBBC, alanine and aspartate aminotransferases, and bilirubin were raised in both hepatoma and viral hepatitis patients. Serum UTC II was reduced in both conditions. Alkaline phosphatase activity was significantly increased in hepatoma. Four significant correlations were observed among these parameters in the hepatoma patients while only one significant correlation was observed in viral hepatitis.

Sequestration of crystalline and endogenous cobalamin by R binders down to the distal ileum in exocrine pancreatic dysfunction

It has been recently shown that crystalline cyanocobalamin in exocrine pancreatic insufficiency is sequestered by R binders down to the proximal jejunum, and that bile inhibits the binding of cobalamin to intrinsic factor. In freshly collected human bile, we have found a single type of apo R binder, with a relative molecular mass of 128 100, a molecular radius of 4.65 nm, and a mean isoelectric point of 3.72. Salivary and biliary holo R binders were incubated with normal human gastric juice and intestinal juice from healthy subjects and patients having exocrine pancreatic insufficiency. No degradation of these two holo R binders occurs with normal gastric juice and intestinal juice from patients after four hours incubation time at 37 degrees C, but a partial degradation of salivary holo R binders and a complete loss of biliary Cbl binding capacity were observed with normal intestinal juice in the same in vitro conditions. We have confirmed in vivo, using a triple-lumened tube, that a part of the salivary and biliary holo R binders remains undegraded down to the distal ileum in two patients with exocrine pancreatic insufficiency. These findings strongly suggest that the enterohepatic circulation of cobalamin is effective in healthy subjects, whereas it is partially interrupted in the patients. They provide a proof that a part of endogenous and crystalline exogenous cobalamin is sequestered to R binders down to the distal ileum, and confirm that the failure to degrade the digestive R binders is responsible for the malabsorption of crystalline cobalamin in exocrine pancreatic dysfunction.

Clinical significance of serum transcobalamins in Protein-energy malnutrition

The serum concentrations of Unsaturated Vitamin B(12) binding (UBBC) capacity and the three individual transcobalamins were measured in 34 malnourished children aged 9 months-5 y. Levels of serum vitamin B12, aspartate aminotransferase, alanine aminotransferase, albumin and total proteins were also estimated. The serum UBBC, Transcobalamin I (TC I), Transcobalamin III (TC III), vitamin B12 and the enzyme activities were significantly higher in the kwashiorkor children when compared with both the marasmic and control children. There was also a marked reduction of serum Transcobalamin II (TC II), albumin and total proteins in the kwashiorkor children. In contrast with kwashiorkor, there was a slight increase of serum TC II in the marasmic children. Their serum UBBC, TC I, TC III and B12 were also raised but not as high as in kwashiorkor. These results are discussed in the light of the hepatic dysfunction in kwashiorkor affecting the production of TC II in the liver, while the elevated serum B12 in Protein-energy malnutrition (PEM) may be due to both hepatic damage and intensified release of TC I as a result of infection.

Abnormalities of serum transcobalamins in sickle cell disease (HbSS) in Black Africa

The unsaturated vitamin B12 binding capacity (UBBC) of serum, the three transcobalamins (TC I, TC II, TC III), and the total leucocyte and neutrophil counts have been studied in paediatric patients with sickle cell disease (SCD). Increase in the level of the binding capacities of TC I and TC II with concomitant increase of UBBC was observed in these children who also had increased total white blood and neutrophil counts. There was a significant reduction in the level of endogenous B12. These abnormalities are discussed in relation to the deficiency of the splenic reticuloendothelial function, immunologic defect, hepatic degenerative changes and aplastic crisis observed in SCD. These results lend support to the view that transcobalamins are involved in the defence mechanism of the body. The significant reduction in serum cobalamin in SCD suggests a higher demand on this vitamin for metabolic functions, especially for the sparing of folate.

Serum transcobalamins in healthy Nigerian children

The unsaturated vitamin B12-binding capacity (UB12BC) and the three transcobalamins (TC I, TC II, TC III) have been studied in the serum of normal healthy Nigerian children. The serum UB12BC level was very high in the children: TC I accounted for 39.5% of UB12BC, TC II accounted for 49.5% and TC III accounted for 11%. The results are discussed in the light of the variations in the distribution of transcobalamins in children from what has been previously reported among the African adults. The high percentage of TC I in the children is discussed in the light of a possible immunological role of this transcobalamin. There was an inverse relationship between TC I and TC II levels. A sex difference in UB12BC and TC I levels was observed. The girls had higher UB12BC and this was due to higher TC I, but the advantage of this is not clear.

In vivo evidence that intrinsic factor-cobalamin complex traverses the human intestine intact

Ingested cyano[57Co]cobalamin was recovered as coupled to intrinsic factor from the jejunum of healthy humans. This vitamin-protein complex and the analogous complex from patients having exocrine pancreatic insufficiency were indistinguishable from each other in terms of molecular radius (3.30 nm), ionic nature (eight well-defined isoproteins isoelectric at pH 4.71, 4.84, 4.90, 5.13, 5.23, 5.31, 5.40 and 5.69), and antigenic structure. These findings indicate that the pancreatic proteases do not alter the intrinsic factor cobalamin complex in vivo. Purified R type protein-cyano [57Co]cobalamin complex recovered from patients with exocrine pancreatic insufficiency was similar to the analogous gastric protein in terms of molecular radius (alpha = 4.78 nm) and types of isoproteins (seven well-defined isoproteins isoelectric at pH 2.70, 3.03, 3.38, 3.74, 3.87, 4.05 and 4.20). However, this R protein complex from patients and the intrinsic factor complex from both control subjects and from patients was comprised of more of the acidic type of isoproteins, thereby supporting the notion that carbohydrate-rich isoproteins are more resistant to digestion in the intestine.

A derivative of R-type cyanocobalamin binding proteins in the human intestine. A candidate antibacterial molecule

Human jejunal fluid contains a protein which has a molecular radius of 3.37 nm, an Mr or 60600 and a mean pI of 3.35 and binds cobalamin with a K of 0.1 . 10(9) l/mol. This protein also couples cobalamin analogues lacking the nucleotide moiety, cross-reacts with R-type protein and is resistant to proteolysis in the intestine. These findings refute the hypothesis that cobalamin-analogue binders are present and effectively inhibit the bacterial uptake of analogues in the intestine.

Cobalamin malabsorption due to nondegradation of R proteins in the human intestine. Inhibited cobalamin absorption in exocrine pancreatic dysfunction

In vivo studies demonstrate that the pancreatic enzymes and the ionic environment in the upper gastrointestinal tract are essential determining factors for transport and absorption of cobalamin in man. Jejunal fluid was aspirated from healthy human volunteers after administration of cyano[57Co]cobalamin preparations. Immunochemical analysis of the aspirates demonstrated that all isotopic vitamin was transferred to a protein that is identical to the gastric intrinsic factor in terms of molecular mass (57,500), ionic nature (mean pI, 5.09), and reactivity with anti-intrinsic factor sera. However, in the aspirates from patients with exocrine pancreatic dysfunction the vitamin was found to be coupled > 60% to a protein identical to R proteins in terms of molecular mass (125,000), ionic nature (mean pI, 3.51), and reactivity with anti-R protein and anti-intrinsic factor sera. The preferential transfer of cobalamin to R proteins in the patients and to intrinsic factor in healthy subjects was associated, respectively, with low and normal levels of pancreatic enzymes in the intestine and these in turn were paralleled respectively by impaired and normal ileal absorption of cobalamin. These findings confirm the suggestion that the formation of unabsorbable cobalamin complexes may be the reason of impaired vitamin absorption in exocrine pancreatic insufficiency. Observations made with other selected patients demonstrate: (a) that decreased enzyme activity and nondegradation of R proteins may also be due to nonactivation of pancreatic zymogens in an acidic pH of the intestinal juice the vitamin transported to the jejunum couples to intrinsic factor when pancreatic function is normal, and to intrinsic factor and R protein in exocrine pancreatic insufficiency. The observations made with these selected patients may explain why not all patients with exocrine pancreatic insufficiency develop imparied cobalamin absorption, and also why the malabsorption is corrected by the administration of bicarbonate in certain patients.

Blocking and binding type antibodies against all major vitamin B12-binders in a pernicious anaemia serum

The simultaneous occurrence of blocking and binding antibodies to intrinsic factor (IF), transcobalamin (TC- II, TC I) and other R type vitamin B12 proteins in the serum of a patient with treated pernicious anaemia (PA) is reported here for the first time. The dialysed and purified immunoglobulin-G (IgG), but not the immunoglobulin-M (IgM), from a PA patient neutralized the total unsaturated vitamin B12 binding capacity (UB12BC) of human gastric juice, saliva and serum and also of rabbit serum, suggesting that the PA IgG contained blocking antibodies against, IF, TC II, TC I and other R-binders. In addition, the PA IgG and IgM preparations contained binding antibodies since they could form macromolecular complexes with 57Co-B12 bound to IF, TC I or TC II so that each one of the latter was totally excluded from Sephadex G-200. The presence of the binding antibodies was further confirmed by the formation of radioactive precipitation lines on agarose with each one of the vitamin B12-binders bound to 58Co-B12. The PA serum did not exhibit any measurable UB12BC after dialysis against 7.5 M guanidine-HCl followed by renaturation with phosphate buffer (pH 7.4). But it did form TC I and TC II complexes with 57Co-B12 when the latter was added during the renaturation step indicating that the serum contained circulating immunoglobulin-TC complexes. The blocking antibodies should be distinguished from the previously described binding antibodies. The blocking of the binding of vitamin B12 to TCs resulted in relatively lower serum vitamin B12 levels in the present case in contrast to the presence of binding antibodies where high serum vitamin B12 levels have been reported. In addition, the binding antibodies form immunocomplexes with TCs which can easily be detected because they can bind radioactive vitamin B12 while the corresponding immunocomplexes of blocking antibodies are hidden because they prevent the binding of the vitamin to TCs.

[Heterogeneity of the gastric intrinsic factor autoantibodies of types I and II]

Variable results were obtained in a study of the immunologic reaction of the intrinsic factor (IF)-autoantibodies (IFA) to the human, hog and rat IF antigens. Effectively, some IFA I were unable to block completely all the binding sites of B12 to IF. As to the IFA II, some did not show a total effectiveness in neutralizing the activity of IF in certain human gastric juices. In another study conducted on patients with pernicious anemia, the antibodies obtained from their sera reacted differently to the hog and rat IF; some reacted identically to homologous and heterologous IF others were less and even not effective on the heterologous IF. From these results it was suggested that, within the two main branches of IFA, there would be subdivided groups with selective effect on different antigenic sites of IF.