Amino acid sequence of horse colipase B

Biochemical and structural comparative study between bird and mammal pancreatic colipases

Three colipases were purified from pancreas of two birds (ostrich and turkey) and one mammal (dromedary). After acidic and/or heat treatment and precipitation by sulfate ammonium and then ethanol, cofactors were purified by Sephadex G-50 gel filtration followed by ion-exchange chromatography first on Mono S and then on Mono Q. One molecular form was obtained from each species with a molecular mass of approximately 10 kDa. Cofactors were not glycosylated. The N-terminal sequences of the three purified cofactors showed high sequence homology. A 90 amino acid sequence of the ostrich cofactor was established based on peptide sequences from four different digests of the denaturated protein using trypsin, chymotrypsin, thermolysin, or staphylococcal protease. This sequence exhibited a high degree of homology with chicken and mammal cofactors. Bile salt-inhibited pancreatic lipases from five species were activated to variable extents by colipases from bird and mammal origins. The bird pancreatic lipase-colipase system appears to be functionally similar to homologous lipolytic systems from higher mammals. Our comparative study showed that mammal colipase presents a lower activation level toward bird lipases than the bird counterpart. Three-dimensional modeling of ostrich colipase suggested a structural explanation of this fact.

High expression in adult horse of PLRP2 displaying a low phospholipase activity

The physiological role of the two lipase-related proteins, PLRP1 and PLRP2, still remains obscure although some propositions have been made concerning PLRP2. In this paper, we report the presence of high amounts of PLRP2 in adult horse pancreas whereas no PLRP1 could be detected. As well, a non-parallel expression of PLRP2 and PLRP1 is observed in adult cat and dog, since no PLRP2 could be detected in these two species. In adult ox, neither PLRP2 nor PLRP1 could be found. These findings are in favor of a different regulation of the expression of the genes encoding pancreatic lipase and the related proteins according to the species. The cDNA encoding horse PLRP2 has been cloned and the protein expressed in insect cells. Both native and recombinant PLRP2 display the same catalytic properties. They possess a moderate lipase activity, inhibited by bile salts and not restored by colipase. Interestingly, they differ from PLRP2 from other species by their very low phospholipase activity indicating that PLRP2 could not be considered as a general phospholipase as previously postulated. This work highlights the variability of the properties of PLRP2 and rises the question of the physiological function of this protein in adult according to the species.

Molecular cloning and expression of two horse pancreatic cDNA encoding colipase A and B

Pancreatic colipase plays an essential role in the intestinal fat digestion by anchoring lipase on lipid/water interfaces in the presence of bile salts. In contrast to other species, two molecular forms of colipase, A and B, have been found in horse. The two corresponding cDNAs were isolated from a horse pancreatic library and their nucleotide sequences were determined. Moreover, for the first time, active colipase has been obtained after transfection of COS cells by either colipase A or B cDNA.

Procolipase mRNA: tissue localization and effects of diet and adrenalectomy

Northern blot analysis has identified procolipase mRNA in rat pancreas, stomach and duodenum. Pancreatic colipase mRNA was increased by high-fat diets. Adrenalectomy increased pancreatic procolipase mRNA, an effect enhanced by high-fat diets. The results suggest that colipase is not unique to the pancreas and that diet and glucocorticoids interact in regulating the transcription of its gene.

Cloning and characterization of rabbit pancreatic colipase

1. Among the digestive enzymes synthesized by pancreas, lipase is the principle lipolytic enzyme which hydrolyses dietary glycerides. 2. For its action it requires a coenzyme, colipase. 3. The molecular mechanisms of the interaction of these two are not fully understood. 4. Further, molecular events that regulate and influence lipid absorption are ill defined. 5. The rabbit is the conventional animal model for the study of lipid absorption. We have undertaken the molecular cloning, and characterization of rabbit pancreatic colipase, the coenzyme for pancreatic lipase. 6. Colipase has been cloned from a gt 11 library of an adult rabbit pancreatic cDNA by probing with an oligonucleotide derived from human colipase sequence. 7. The total reading frame consists of 321 nucleotides coding for 90 amino acids of the functional protein and 17 nucleotides of the leader peptide. 8. Northern blot analysis revealed a distinct band around 0.5 kb. Comparison with other species revealed an over all homology of 75% at the nucleotide level. 9. At the amino acid level highest conservation is observed at the lipase-binding region (AA 53-73). 10. Rabbit enzyme also retained the N-terminal pentapeptide of its preform. 11. The regions of homology and conservation may aid to define the sites of interaction of colipase with lipase.

Separation and characterization of the precursor and activated forms of porcine and human pancreatic colipase by reversed-phase liquid chromatography

Reversed-phase liquid chromatography was used as an alternative method for the characterization of the precursor and activated forms of porcine and human pancreatic colipase. Using a Beckman Ultrasphere column with an increasing acetonitrile gradient in 0.1% trifluoroacetic acid, it was possible to obtain well-resolved separation of the precursor form of colipase (procolipase) from its trypsin-activated derivative. This protocol was used (1) to study the activation of porcine procolipase by trypsin or thrombin in vitro, (2) to assess the homogeneity of porcine colipase preparations used in tridimensional structure studies and in combination with immunoaffinity chromatography, (3) to identify the form of colipase present in samples of human pancreatic juice.

Conformational prediction studies on pancreatic colipase

Comparison of the primary structures of pancreatic colipases from man, pig, horse and rat shows a high degree of homology between proteins. Fifty-two out of the 95 residues of the polypeptide are identical. All colipases contain 10 half-cystines which are located at invariant positions. The secondary structure of colipases has been predicted from the sequence using the statistical method of Chou and Fasman and the method of Gibrat, Garnier and Robson based on information theory. Predictions indicate that colipases have a low content of alpha-helix and beta-strand structure. The two segments at positions 7-10 and 56-59, assumed to be part of the lipid binding domain, have predicted beta-sheet conformation and should be in close spatial vicinity to each other in the proteins. Four beta-turns are predicted in all colipases at positions 3-6, 46-49, 61-64, and 81-84. They might contribute, with the five disulfide bridges, to a tight packing of the protein molecule. Surface residues and major sequential antigenic determinants of mammalian colipases have been predicted using methods based either on hydrophilicity/hydropathy scales or amino acid mutability. From these studies, it appears that colipases exhibit large conformational homologies. In the absence of data on the tertiary structure of colipase, predictive methods, together with physico-chemical and immunological studies, provide valuable information on the conformation of the protein in relation to the topology of residues involved in the functional and antigenic sites.

Development of enzyme-linked immunosorbent assay for free human pro-colipase activation peptide (APGPR)

Human pancreatic colipase is secreted as the inactive form procolipase. Activation involves tryptic cleavage of an N-terminal pentapeptide Ala-Pro-Gly-Pro-Arg (APGPR) which is known as procolipase activation peptide (CLAP). N-terminally haptenised synthetic APGPR was used to generate specific C-terminally directed anti-APGPR antibodies. The antiserum was used to develop a competitive enzyme linked immunosorbent assay (ELISA) specific for free CLAP with a detection limit of 12 nmol/l and an intra-assay coefficient of variation (CV) of 3.28% and an inter-assay CV of 5.82%. The release of immunoreactive CLAP from human pancreatic juice and chicken pancreas upon trypsinisation was demonstrated, as well as the absence of reactivity of the antisera with procolipase from which the CLAP is released. APGPR was found to be unstable in biological fluids. Immunoreactivity is rapidly lost with half life of 5 min and 4 h in human serum and urine respectively. This loss of reactivity can be significantly slowed by the addition of 20 mmol/l Zinc ions (Zn2+), while ethylenediaminetetra-acetic acid (EDTA) and other protease inhibitors were ineffective. In serum the moiety responsible for loss of immunoreactivity was found to have an estimated molecular mass of 200,000-300,000 Da. CLAP assay specifically reports procolipase activation and may help elucidate the mechanism of satiety as well as contribute to the recognition and understanding of the role of procolipase activation in diseases states such as pancreatitis.

Assignment of the human pancreatic colipase gene to chromosome 6p21.1 to pter

Pancreatic colipase is a 12-kDa polypeptide cofactor for pancreatic lipase (EC 3.1.1.3), an enzyme essential for the absorption of dietary long-chain triglyceride fatty acids. Colipase is thought to anchor lipase noncovalently to the surface of lipid micelles, counteracting the destabilizing influence of intestinal bile salts. Using primers derived from the known amino acid sequence, we have used the polymerase chain reaction to produce a cDNA clone corresponding to the complete coding region of the human procolipase mRNA. Southern blot analysis of genomic DNA from a panel of mouse-human somatic cell hybrids indicated that the colipase gene (CLPS) resides on human chromosome 6. Further analysis of somatic cell hybrids carrying chromosome 6 translocations permitted regional localization of CLPS to the 6p21.1-pter region.

Amino acid sequence and molecular modelling of a thermostable two (4Fe-4S) ferredoxin from the archaebacterium Methanococcus thermolithotrophicus

The amino acid sequence of a two (4Fe-4S) ferredoxin from the methanogenic bacterium Methanococcus thermolithotrophicus (FdMt) has been determined. This thermostable protein comprises 60 amino acid residues (Mr 6541) and two (4Fe-4S) clusters chelated to the protein through the eight cysteines. FdMt contains a relatively high number of lysines [5], threonines [4] and valines [10]. The three-dimensional molecular model generated from the Peptococcus aerogenes X-ray structure keeps the characteristic overall ferredoxin folding thanks to complementary substitutions of residues of the hydrophobic core. The major structural features of the model are the different environments of both clusters, and the patch of three lysines at one end of the molecule. The possible role of several structural factors in the thermostability of the protein is discussed.

Rat pancreatic colipase mRNA: nucleotide sequence of a cDNA clone and nutritional regulation by a lipidic diet

A cDNA clone encoding rat pancreatic colipase was isolated using as a probe a synthetic deoxyoligonucleotide corresponding to a highly conserved amino acid sequence region in colipases from other species. The cloned messenger codes for a protein of 95 amino acids plus a signal peptide of 17 amino acids. The structure of the full-length cDNA was also determined and the corresponding amino acid sequence showed a high degree of homology with those of other known colipases. Quantification of the homologous mRNA in the pancreas of animals fed a high-lipid diet was consistent with a specific though moderate induction of colipase messenger by the nutritional manipulation.

Inhibitory properties and antigenic specificity of monoclonal antibodies to pancreatic colipase

To understand the mechanism by which colipase acts as a protein cofactor for anchoring pancreatic lipase at triacylglycerol/water interface, we have used an immunochemical approach. Ten monoclonal antibodies (Mabs) against porcine pancreatic procolipase were produced. Purified immunoglobulins and Fab fragments were studied for their capacity to inhibit colipase-dependent lipase activity. These studies were carried out by using procolipase, the secretory form of the cofactor, and its trypsin-treated form obtained by removal of the amino terminal pentapeptide by trypsin. Reactivities of Mabs with both forms of the cofactor were also studied by immunoenzymatic methods. Mabs 6.1, 49.20. 75.8, 270.13 and 419.1 were found to inhibit lipolysis by preventing the binding of procolipase or trypsin-treated colipase to the lipid substrate. Mab 72.11 inhibited procolipase binding but had no effect on trypsin-treated colipase. Mab 72.11 reacted with procolipase in ELISA but showed no reactivity with trypsin-treated colipase. Finally, preincubation of Mab 72.11 with porcine procolipase prevented specific cleavage at the Arg5-Gly6 bond by trypsin. It could be concluded, that the five first residues of procolipase are structural elements of the antigenic determinant recognized by Mab 72.11. Results of ELISA additivity tests (cotitrations) further indicated that epitopes for Mabs 6.1, 72.11, 270.13 and 419.1 and for Mabs 49.20 and 75.8 are located in two distinct antigenic regions of the procolipase molecule. It appears then that the lipid binding domain of the pancreatic lipase protein cofactor comprises two regions. The first region corresponds to the amino terminal fragment of the protein. The second region is likely identical with the peptide segment at position 51-59 as previously hypothesized from NMR and spectrophotometric studies. Studies carried out on procolipase chemically modified at tyrosine residues provided evidence that epitopes for Mabs 49.20 and 75.8 are in or close to the region which contains tyrosines at positions 55 and 59, and that the two peptide regions essential for interfacial binding are spatially adjacent in the procolipase and the trypsin-treated form of the cofactor. General conclusions are in accordance with the location of antigenic regions of procolipase determined by predictive methods.

Cloning and sequencing of the gene encoding cytochrome c553 from Desulfovibrio vulgaris Hildenborough

The gene encoding cytochrome c553 from Desulfovibrio vulgaris Hildenborough was cloned by using two synthetic deoxyoligonucleotide probes. The amino acid sequence derived from the sequence of the gene differs from that reported by Bruschi and LeGall (Biochim. Biophys. Acta 271:48-60, 1972). Renewed protein sequencing confirmed the correctness of the DNA-derived sequence. The gene sequence indicates cytochrome c553 to be synthesized as a precursor protein with an NH2-terminal signal sequence of 24 residues.

Comparative studies of polyhemic cytochromes c isolated from Desulfovibrio vulgaris (Hildenborough) and Desulfovibrio desulfuricans (Norway)

Cytochrome c3 (Mr 26,000) has been characterized in Desulfovibrio vulgaris (Hildenborough) and its properties compared with polyhemic cytochromes c isolated from the same organism and from D. desulfuricans (Norway). It can be described as an octaheme cytochrome c3 constituted of two identical subunits. Absorption spectrum is similar to cytochrome c3 (Mr 13,000) and individual redox potentials have an average value of -180 mV.3 The N terminal sequence is compared with an homologous cytochrome isolated from D. desulfuricans Norway.

Minireview on pancreatic lipase and colipase

By hydrolyzing the dietary triacylglycerols, pancreatic lipase causes catalysis in heterogeneous medium. In vivo, lipase action cannot take place without colipase due to the presence of bile salts. The cofactor enables lipase anchoring to the water-lipid interface. The lipase-colipase system furnishes an excellent example of specific interactions (protein-protein and protein-lipid). The studies of lipase catalytic properties brought to light the importance of certain parameters related to the 'quality of the interface'. The structure-function relationship analyses revealed a certain number of functional amino acid residues in lipase and colipase involved either in the catalytic site of the enzyme or in the recognition sites (lipase-colipase and protein-interface). Comparisons of the sequences of lipases derived from different sources display interesting similarities in certain cases.

The activation peptide of pancreatic procolipase decreases food intake in rats

Pancreatic procolipase is a cofactor for lipase and necessary for optimal fat digestion in the intestine during a meal. It is activated by trypsin in the intestine during release of an activation peptide, with the sequence Val-Pro-Asp-Pro-Arg in rat. This peptide, in the following termed VPDPR, was found to decrease food intake in rats. The human procolipase activation peptide with the sequence Ala-Pro-Gly-Pro-Arg (APGPR) had no effect on food intake in rats, nor the trypsinogen activation peptide with the sequence Phe-Pro-Val-Asp-Asp-Asp-Asp-Lys (FPVDDDDK). Procolipase added to standard pellets decreased the daily food intake in rats, whereas colipase added to pellets had no effect.

The role of aromatic side chain residues in micelle binding by pancreatic colipase. Fluorescence studies of the porcine and equine proteins

Fluorescence techniques have been employed to study the interaction of porcine and equine colipase with pure taurodeoxycholate and mixed micelles. Nitrotyrosine-55 of porcine colipase is obtained by modification with tetranitromethane (low excess, in the presence of taurodeoxycholate) of the protein followed by gel filtration and ion-exchange chromatography. Verification of the residue modified was obtained by h.p.l.c. peptide purification and sequence analysis. Reduction and quantitative reaction with dansyl chloride yields a fluorescent derivative that is twice as active in conjunction with lipase as is native colipase and that exhibits a strong emission band at 550 nm. Addition of micellar concentrations of taurodeoxycholate causes a 4.3-fold increase in the emission maximum as well as a 70 nm blue shift to 480 nm. Inclusion of oleic acid to form a mixed micelle reduces these spectral effects. Scatchard analysis of the data yield a Kd of 6.8 X 10(-4) M and a single colipase-binding site for taurodeoxycholate micelles. The data, by analogy to a phospholipase system, are consistent with a direct insertion of dansyl-NH-tyrosine-55 into the micelle. The presence of a single tryptophan residue (Trp-52) in equine colipase provides an intrinsic fluorescent probe for studying protein-micelle interaction. The emission maximum of horse colipase at 345 nm indicates a solvent-accessible tryptophan residue which becomes less so on binding of micelles. A blue shift of 8 nm and a 2-fold increase in amplitude is indicative of a more hydrophobic environment for tryptophan induced by taurodeoxycholate micelles. There is also a decrease in KSV for acrylamide quenching in the presence of micelles, which further supports a loss of solvent accessibility. The most dramatic pH effects are observed with KI quenching, and may indicate the presence of negative charges near Trp-52.

Production and characterization of four monoclonal antibodies against porcine pancreatic colipase

Four monoclonal antibodies directed against porcine colipase have been generated by hybridization of myeloma cells with spleen cells of BALB/c immunized mice. Antibodies were screened by binding to immobilized colipase in a solid-phase assay. Monoclonal antibodies were purified by affinity chromatography on colipase coupled to Sepharose. All monoclonal antibodies are of the IgG1 class with high affinity for the antigen. The dissociation constant of the complex formed in solution between porcine colipase and antibody varied from 1.1 X 10(-10) M to 1.8 X 10(-8) M. Epitope specificity was studied for each antibody and in pairs with an enzyme-linked immunosorbent assay (ELISA). Results indicate that the four monoclonal antibodies react with at least three different antigenic regions of colipase. Finally, three monoclonal antibodies were found to be potent inhibitors of colipase activity. Antiporcine monoclonal antibodies appear to be suitable probes for studying the lipid affinity site of the protein cofactor of pancreatic lipase.

Complete amino-acid sequence of the natural ATPase inhibitor from the mitochondria of the yeast Candida utilis

The complete alignment of the 63 residues of the mitochondrial ATPase inhibitor from the yeast Candida utilis has been determined. The sequence study was carried out mainly by automatic (liquid and solid-phase) methods. Peptides were obtained by enzymatic digestion with clostripain and purified by reverse-phase high-performance liquid chromatography. The ATPase inhibitor contains three sets of repetitive sequences and eight clusters of charged residues, as also found in the inhibitor of Saccharomyces cerevisiae, with which it shares 58.7% homology of conserved residues. When the two yeast ATPase inhibitor sequences were compared to that of beef heart, 20 residues remained common to the three alignments, although the latter protein contained a long histidine-rich insertion, only found in this inhibitor. Most of the homologous residues were clustered near the center of the protein, which by partial proteolytic digestion of the beef heart ATPase inhibitor [Dianoux, A.C. et al. (1982) FEBS Lett. 140, 223-228] has already been shown to be involved in the biological function.

Spectrofluorimetric study of the bile salt micelle binding site of pig and horse colipases

Pig and horse colipases contain three tyrosine residues. In addition, horse colipase possesses a tryptophan residue. Some of the tyrosine residues are involved in the association of colipase and a bile salt micelle. The present report demonstrates that the aromatic residues responsible for colipase fluorescence are in an aqueous environment. In the presence of bile salt micelles, changes in colipase fluorescence properties indicate that the intrinsic fluorophores are located in a more hydrophobic environment upon colipase-micelle complex formation. In addition, the fluorescence of an NBD group fixed on lysine 60, which is very close to the aromatic region in the pig colipase, is also altered in the presence of micelles. These results show that the micelle binding site is not limited to the tyrosine residues but may be broadened to adjacent residues such as lysine 60 and also tryptophan 52 in horse colipase.

Amino acid sequence of [2Fe-2S] ferredoxin from Clostridium pasteurianum

The complete amino acid sequence of the [2Fe-2S] ferredoxin from the saccharolytic anaerobe Clostridium pasteurianum has been determined by automated Edman degradation of the whole protein and of peptides obtained by tryptic and by staphylococcal protease digestion. The polypeptide chain consists of 102 amino acids, including 5 cysteine residues in positions 11, 14, 24, 56, and 60. The sequence has been analyzed for hydrophilicity and for secondary structure predictions. In its native state the protein is a dimer, each subunit containing one [2Fe-2S] cluster, and it has a molecular weight of 23,174, including the four iron and inorganic sulfur atoms. The extinction coefficient of the native protein is 19,400 M-1 cm-1 at 463 nm. The positions of the cysteine residues, four of which are most probably the ligands of the [2Fe-2S] cluster, on the polypeptide chain of this protein are very different from those found in other [2Fe-2S] proteins, and in other ferredoxins in general. In addition, whole sequence comparisons of the [2Fe-2S] ferredoxin from C. pasteurianum with a number of other ferredoxins did not reveal any significant homologies. The likely occurrence of several phylogenetically unrelated ferredoxin families is discussed in the light of these observations.

Partial amino acid sequence of human pancreatic stone protein, a novel pancreatic secretory protein

Pancreatic stone protein (PSP) is the major organic component of human pancreatic stones. With the use of monoclonal antibody immunoadsorbents, five immunoreactive forms (PSP-S) with close Mr values (14,000-19,000) were isolated from normal pancreatic juice. By CM-Trisacryl M chromatography the lowest-Mr form (PSP-S1) was separated from the others and some of its molecular characteristics were investigated. The Mr of the PSP-S1 polypeptide chain calculated from the amino acid composition was about 16,100. The N-terminal sequences (40 residues) of PSP and PSP-S1 are identical, which suggests that the peptide backbone is the same for both of these polypeptides. The PSP-S1 sequence was determined up to residue 65 and was found to be different from all other known protein sequences.

Nucleotide sequence of the promoter and amino-terminal encoding region of the Escherichia coli pepN gene

The nucleotide sequence of the region probably responsible for regulation of pepN expression and of the region encoding the amino-terminal part of aminopeptidase N, has been determined. The transcription start site was identified by S1 nuclease mapping. All features of the promoter are those of a weak promoter and no obvious structure responsible for regulation was identified, although a possible Pho box is located 63 base pairs upstream from the Pribnow box. The reading frame was unambiguously determined by purifying the protein and by sequencing the first 21 NH2-terminal residues. The NH2-terminal region of aminopeptidase N does not contain any fragment resembling signal sequence and the protein is not produced in a precursor form. A divergent promoter, which might be that of pncB, encoding the nicotinic acid phosphoribosyltransferase (P. Terpstra, personal communication), has also been identified, which allows the assignment of the gene organization in this chromosomal region as ompF asnS pncB pepN.

Further results on lipase-colipase interactions studied by affinity chromatography

Affinity chromatography of lipase on a colipase-coupled gel was studied in the present paper. The elution volume of the associable lipase increased when the loaded amount decreased. A KD value of 1.9 X 10(-6) M at pH 6.2 was thus deduced. A minimum value of 1.5 X 10(-6) M was obtained at pH 5.1-5.3. Mixed micelles associated with coupled colipase, but no modifications of lipase-colipase interactions took place when mixed micelles were added to the elution buffer. DMMA-modified coupled colipase failed to interact with lipase, owing to the specific orientation of the modified cofactor in the gel.

Purification and characterization of pancreatic colipase from the dogfish (Squalus acanthius)

Pure colipase from dogfish (Squalus acanthius) was obtained from an extract of pancreatic gland. It has a high isoelectric point (10.2) and the molecular weight was calculated to be 9108-9383. The N-terminal sequence was shown to be Gly-Leu-Phe-Leu-Asn-Leu-Ser-Ala-Gly-Glu-Leu-Cys-Val-Gly-Ser-Phe-Gln -Cys-Lys-Ser-Ser-Cys-Cys-Gln-Arg-Glu-Thr-Gly-Leu-Ser-Leu-Ala -Arg-Cys-Ala-. This sequence shows great homology with colipases from man, horse, pig and hen. There were indications of the existence of a proform of dogfish colipase. The propeptide was found to be Ala-Pro-Glu-Arg.

Evidence for the existence of procolipase in chicken pancreas and pancreatic juice

Purified antibodies raised against chicken colipase were coupled to Sepharose 4B and colipase was isolated in a single step by immunoaffinity chromatography from an extract of chicken pancreas prepared under conditions where trypsin activation is avoided. The purified protein has a single amino terminal residue of alanine and its biochemical properties are similar to those of the precursor form of colipase (procolipase) previously isolated from porcine and equine pancreas or pancreatic juice. Further evidence for the existence of procolipase was obtained from kinetic studies of the hydrolysis of the Intralipid emulsion by untreated and trypsin-treated chicken pancreatic juice.

The primary sequence of human pancreatic colipase

The amino acid sequence of an activated colipase purified from human pancreas was determined. The protein consists of a single polypeptide chain of 86 amino acids (human colipase86) and has a molecular weight of 9289. The sequence was determined by automated Edman degradation of the reduced and S-carboxymethylated protein and of two CNBr peptides. Sequence determination of porcine procolipase II was also performed, which showed that in the original sequence determination apparently two residues were missed. These residues were determined to be a leucine at position 37 and a serine in position 50. For comparison with porcine and equine procolipases, the residues composing human colipase are numbered from 6 to 91. No human procolipase has been isolated so far. The colipases from man, pig, horse and chicken show a high degree of homology: human colipase differs from the other proteins by substitutions of 19 (porcine), 24 (equine A) and 21 (equine B) residues, respectively.

Nitration of the tyrosine residues of porcine pancreatic colipase with tetranitromethane, and properties of the nitrated derivatives

The nitration of the long form (N-terminal valine) of porcine pancreatic colipase with tetranitromethane was investigated under a variety of conditions. Fractionation of the nitrated monomers on DE-cellulose led to well-defined derivatives containing one, two and three nitrotyrosines per mol. Automated Edman degradation of the nitrated peptides, especially that of the staphylococcal proteinase peptide (49-64) showed that Tyr-54 was nitrated very fast under all conditions. This residue was the only one to be nitrated in water. Partial nitration of Tyr-59 was induced by bile salt micelles, while both Tyr-59 and Tyr-58 reacted extensively in the presence of lysophosphatidylcholine micelles (in which tetranitromethane is concentrated 150-fold compared to water) or of a liquid tetranitromethane-water interface. The strong negative Cotton effect at 410 nm which has already been observed using unfractionated preparations of nitrated colipase (Behnke W.D. (1982) Biochim. Biophys. Acta 708, 118-123) is linked with the nitration of Tyr-59 and it is markedly reduced by taurodeoxycholate micelles, suggesting a conformational change induced by the micelles in the tyrosine region. Moreover, the pKa of the nitrotyrosine residues in nitrated colipase is the same as that of free nitrotyrosine (pKa = 6.8) and it is shifted to 7.6 in the presence of taurodeoxycholate micelles. Micelles protected colipase against polymerization during nitration. These data suggest that Tyr-58 and Tyr-59 are part of the interface recognition site of colipase. The participation of Tyr-55 in binding is not excluded. The upwards nitrotyrosine pKa shift in the colipase micelle complex may explain why nitrated colipase can reactivate lipase in a triacylglycerol-taurodeoxycholate system at pH 7.5.

Studies on the immunological cross-reactivity of various pancreatic colipases. Isolation by immunoaffinity chromatography of a single form of procolipase from porcine pancreas

Antibodies against porcine procolipase B were produced in rabbits. The antiserum was used to immunoinactivate various forms of native and trypsin-treated porcine colipase. Our results indicate that all forms of the porcine cofactor bind to anti-porcine procolipase B antibodies. Human colipase showed lower affinity for the antibodies than porcine colipase. No cross-reactivity was observed between pig and horse, cow, dog or chicken colipases. Immunological studies on porcine colipase, carried out in the presence of lipid, provided evidence that antibodies bind to colipase at or near the lipase binding site. The binding of antibodies to colipase is not affected by the adsorption of the cofactor at a lipid interface. Using a predictive method for identification of the antigenic determinants, it was found that, in pig colipase, regions at positions 42-48 and 70-74 might represent antigenic sites. In the horse protein, the peptide segment 42-48 was also recognized as a possible antigenic site. An immunoadsorbent gel column was prepared for a one-step isolation of porcine colipase. In contrast to purification methods described so far, immunoaffinity chromatography yielded only one form of the porcine cofactor when starting from a pancreatic extract. This protein preparation has structural, biochemical and immunochemical properties similar to that of porcine procolipase A previously isolated from pancreas in the presence of detergent.

Primary structure of the two (4 Fe-4 S) clusters ferredoxin from Desulfovibrio desulfuricans (strain Norway 4)

The primary structure of a ferredoxin isolated from D. desulfuricans Norway strain, which we called ferredoxin II (Fd II) has been elucidated. This ferredoxin is a dimer constituted of two identical subunits of molecular weight 6000. In ferredoxin II two (4 Fe-4 S) centers are present per subunit instead of one (Fe-S) center as is the case for the other ferredoxins isolated from Desulfovibrio and for Fd I from the same organism. The comparison of amino-acid sequences shows that ferredoxin II presents more homologies with clostridial type ferredoxin than with the ferredoxins from D. gigas and D. africanus.

Binding between immobilized anti-colipase purified antibodies and colipase. Radioimmunoassay of colipase from pig plasma and pancreatic juice

Procedures for purification of porcine colipase II (Gly6-Gly89) and for obtaining purified anti-colipase antibodies are described. The interactions between antibodies immobilized on an Ultrogel AcA 22 column and colipase were investigated and colipase radioimmunoassay carried out. The immobilized antibody-colipase binding was preserved in the presence of mixed micelles, lipase, or both when added to the elution mixture. Bound colipase maintained its capability of interacting with mixed micelles, but not with lipase in either the presence or the absence of mixed micelles. It could be inferred that the antigenic site(s) is independent of the interfacial recognition site and close to the site of lipase recognition. Results are reported suggesting that one or both colipase histidyl residue-containing sequences are involved as antigenic determinant(s). Immunoreactive colipase, bound to a macromolecular protein complex, was found in the plasma of pig. This finding could be explained by an endocrine 'leakage' of colipase from the exocrine pancreatic cell rather than by passage through the intestinal mucosa.

Pancreatic colipase: crystallographic and biochemical aspects

A detailed study of the crystallization of hog and horse colipases has been undertaken. Several crystallographic varieties have been obtained and a 0.3-nm resolution structure determination is actually in progress. The sequence of the A form of horse colipase (one methionine) is given. From spectrophotometric experiments and sequence comparisons, the involvement of the aromatic residue in position 52 in the micelle binding site has been demonstrated.

The amino acid sequence of the hydrophobic anchor of rabbit intestinal brush border aminopeptidase N

The N-terminal sequence (14 residues) of the detergent form of rabbit intestinal aminopeptidase N was shown to be different from that of the protease form of the same enzyme and to be mostly hydrophobic. This finding is fully consistent with a previous assumption according to which this class of enzymes may be anchored to the brush border membrane by their N-terminus. This special mode of assembly may be facilitated by a positively charged lysine residue near the beginning of the sequence (Lys 4) just before an uninterrupted stretch of hydrophobic amino acids.