Dogfish insulin. Primary structure, conformation and biological properties of an elasmobranchial insulin

The insulin gene as an energy homeostasis biomarker in Yangtze sturgeon (Acipenser dabryanus)

Insulin plays an important role in maintaining energy homeostasis and has the potential to be an indicator of energy homeostasis in the Yangtze sturgeon, Acipenser dabryanus. In this study, the Yangtze sturgeon insulin (Adinsulin) was cloned and characterized. To evaluate the possibility of insulin as an energy state assessment indicator, quantification real-time PCR (qRT-PCR) was used to evaluate expression changes in different tissues (the whole brain, esophagus, cardiac stomach, pyloric stomach, pyloric caeca, duodenum, valvula intestine, rectum, liver, pancreas, spleen, kidney, heart, muscle, gill and eye) from 6 fish (average weight 325.7 ± 22.3 g) and in three experiments including postprandial, fasting and re-feeding, and glucose tolerance treatment in which fish were divided into two groups including a group that administered a glucose solution (1 ul/g body weight) and another group that administered sterile water as control. In these three experiments, 6 fish were sampled, respectively, then been used to evaluate expression changes of insulin. All fish in feeding groups were fed in tanks (60.0 cm × 50.0 cm × 40.0 cm) with a commercial diet (crude protein ≥ 40%, crude fat ≥ 12%, coarse fiber ≤ 6%, crude ash ≤ 18%; TONGWEI CO., LTD, China) once a day at 16:00. The result showed that Adinsulin was highly expressed in the pancreas, which was the basis for the next experiment to use the pancreas as the test target. Adinsulin expression significantly increased 1 h after feeding and decreased rapidly after 3 h of feeding, but it was still significantly higher than that of the group without feeding (P < 0.01). Compared to the feeding group, the expression of Adinsulin was significantly reduced in the fasting group of 3 days (P < 0.01), 6 days (P < 0.01), 10 days (P < 0.05), 11 days (P < 0.05) and 13 days (P < 0.01) and was no significant difference in re-feeding for 1st day, 2nd day and 4th day, but there was difference between re-feeding group and fasting group. After glucose tolerance treatment, serum glucose levels increased significantly (P < 0.05), accompanied by a significant increase (P < 0.001) in insulin expression. This study result shows that insulin has the capacity to measure the energy homeostasis of Yangtze sturgeon. Further development of detection methods for sturgeon plasma or serum insulin will avoid slaughtering animals and is more practical in energy homeostasis assessment.

New insights into the signaling system and function of insulin in fish

Fish have provided essential information about the structure, biosynthesis, evolution, and function of insulin (INS) as well as about the structure, evolution, and mechanism of action of insulin receptors (IR). INS, insulin-like growth factor (IGF)-1, and IGF-2 share a common ancestor; INS and a single IGF occur in Agnathans, whereas INS and distinct IGF-1 and IGF-2s appear in Chondrichthyes. Some but not all teleost fish possess multiple INS genes, but it is not clear if they arose from a common gene duplication event or from multiple separate gene duplications. INS is produced by the endocrine pancreas of fish as well as by several other tissues, including brain, pituitary, gastrointestinal tract, and adipose tissue. INS regulates various aspects of feeding, growth, development, and intermediary metabolism in fish. The actions of INS are mediated through the insulin receptor (IR), a member of the receptor tyrosine kinase family. IRs are widely distributed in peripheral tissues of fish, and multiple IR subtypes that derive from distinct mRNAs have been described. The IRs of fish link to several cellular effector systems, including the ERK and IRS-PI3k-Akt pathways. The diverse effects of INS can be modulated by altering the production and release of INS as well as by adjusting the production/surface expression of IR. The diverse actions of INS in fish as well as the diverse nature of the neural, hormonal, and environmental factors known to affect the INS signaling system reflects the various life history patterns that have evolved to enable fish to occupy a wide range of aquatic habitats.

Purification, characterization, and biological activity of insulins from the spotted dogfish, Scyliorhinus canicula, and the hammerhead shark, Sphyrna lewini

Insulin was purified from pancreatic extracts of two elasmobranch species belonging to different families in the order Carcharhiniformes, the European spotted dogfish, Scyliorhinus canicula (Scyliorhinidae), and the hammerhead shark, Sphyrna lewini (Carcharhinidae). The amino acid sequence of dogfish insulin was established as A-chain GIVDHCCRNT(10)CSLYDLEGYC(20)NQ and B-chain LPSQHLCGSH(10)LVETLYFVCG(20)QKGFYYVPKV(30). The primary structure of hammerhead shark insulin was similar to that of dogfish insulin with only 2 amino acid substitutions at A8 (R --> H) and B30 (V --> I). The elasmobranch insulins were markedly different from human insulin (17 amino acid substitutions) but all the residues in human insulin that are believed to be important in determining the receptor binding conformation (B6, B8, B11, B13, B23, B24, B25, A2, A3, and A19) have been conserved in the elasmobranch insulins with the exception of the conservative substitution Phe --> Tyr at B25. Consistent with this, dogfish and human insulin showed almost identical binding affinity to the recombinant solubilized human insulin receptor (K(D) values of 14.0 and 18.6 pM, respectively; relative potency 133%). Previous studies have shown that bovine insulin produces severe and sustained hypoglycemia in elasmobranchs but the effect is of slow onset. Bolus arterial injections of dogfish insulin (10 nmol x kg(-1)) into unanesthetized, fasting dogfish (n = 9) produced no changes in blood glucose, 3-hydroxybutyrate, and acetoacetate concentrations over a 4-h period. In a second series of experiments (n = 7), dogfish insulin (10 nmol x kg(-1)) produced a significant (P < 0.05) fall in blood glucose after 12 h that persisted for at least 48 h, but no change in ketone body concentrations. The data indicate that the metabolic actions of an endogenous elasmobranch insulin in an elasmobranch are similar to those previously described for mammalian insulin.

Evolution of the insulin molecule: insights into structure-activity and phylogenetic relationships

The conformation of insulin in the crystalline state has been known for more than 30 years but there remains uncertainty regarding the biologically active conformation and the structural features that constitute the receptor-binding domain. The primary structure of insulin has been determined for at least 100 vertebrate species. In addition to the invariant cysteines, only ten amino acids (GlyA1, IleA2, ValA3, TyrA19, LeuB6, GlyB8, LeuB11, ValB12, GlyB23 and PheB24) have been fully conserved during vertebrate evolution. This observation supports the hypothesis derived from alanine-scanning mutagenesis studies that five of these invariant residues (IleA2, ValA3, TyrA19, GlyB23, and Phe24) interact directly with the receptor and five additional conserved residues (LeuB6, GlyB8, LeuB11, GluB13 and PheB25) are important in maintaining the receptor-binding conformation. With the exception of the hagfish, only conservative substitutions are found at B13 (Glu --> Asp) and B25(Phe --> Tyr). In contrast, amino acid residues that were also considered to be important in receptor binding based upon the crystal structure of insulin (GluA4, GlnA5, AsnA21, TyrB16, TyrB26) have been much less well conserved and are probably not components of the receptor-binding domain. The hypothesis that LeuA13 and LeuB17 form part of a second receptor-binding site in the insulin molecule finds some support in terms of their conservation during vertebrate evolution, although the site is probably absent in some hystricomorph insulins. In general, the amino acid sequences of insulins are not useful in cladistic analyses especially when evolutionary distant taxa are compared but, among related species in a particular order or family, the presence of unusual structural features in the insulin molecule may permit a meaningful phylogenetic inference. For example, analysis of insulin sequences supports monophyletic status for Dipnoi, Elasmobranchii, Holocephali and Petromyzontiformes.

Isolation and characterization of insulin in Russian sturgeon (Acipenser guldenstaedti)

Insulin was isolated from the pancreas of Chondrostean fish, the Russian sturgeon, Acipenser guldenstaedti, by acid-ethanol extraction followed by ion-exchange and reverse-phase high-performance liquid chromatographies. The amino acid sequence determined by automated Edman degradation is as follows: A-chain (21-amino-acid peptide), H-Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Ser-Pro-Cys-Ser-Leu-Tyr-Asp-Leu-Glu-As n-Tyr-Cys-Asn-OH; and B-chain (31-amino-acid peptide), H-Ala-Ala-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala-Leu-Tyr-Leu-Va l-Cys-Gly-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Asn-Lys-Val-OH. The sturgeon insulin appears to be identical with one of two forms of paddlefish insulin and differs from the other form by a single substitution in the A-chain, Asp15: His15. The amino acid sequence of sturgeon insulin is more similar to the amino acid sequence of mammalian insulins than of other fish insulins. Sturgeon insulin showed parallel but weaker displacement than porcine insulin and pink salmon insulin in their respective radioimmunoassays and was less potent than porcine insulin in displacing radiolabeled porcine insulin bound to partially purified rat liver plasma membranes.

Identification of a glycosylated relaxin-like molecule from the male Atlantic stingray, Dasyatis sabina

The alkaline gland fluid of the Atlantic stingray (Dasyatis sabina) contains a molecule that cross-reacts weakly to anti-porcine relaxin antibodies. This material was isolated and purified to homogeneity by reversed-phase high-performance liquid chromatography. In SDS gel electrophoresis, the molecule showed an apparent molecular mass of 13 kDa which upon reduction formed two polypeptide chains of 4 and 9 kDa, respectively. Sequence analyses revealed a 27-amino acid residue A chain and a 54-amino acid residue B chain which contained an N-glycosylation site in position B37. The distribution of the six cysteines and possibly the disulfide bonding is identical to that found in insulins and most relaxins. Although the stingray relaxin-like molecule contains the structurally relevant glycine residues within the A chain, in the midregion of the B chain it has only one of the two requisite binding site arginines, which explains the lack of relaxin bioactivity in standard mammalian assays. Stingray relaxin is the first member of the relaxin family identified in a nonhomeotherm male. Carbohydrate analysis of relaxin revealed an N-linked asialo, agalacto, bisected biantennary, and a core-fucosylated oligosaccharide in the position of Asn B37 which makes it the first reported glycosylated relaxin-like molecule.

Primary structure of insulin from the african lungfish, Protopterus annectens

Among the extant Sarcopterygii, the interrelationship between the Dipnoi (lungfishes), Actinistia (coelacanths), and Tetrapoda (tetrapods) is controversial. Insulin has been purified from an extract of the pancreas of the African lungfish Protopterus annectens and its primary structure established as A-chain, Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Lys-Pro10-Cys-Ser-Leu- Tyr -Glu-Leu-Glu-Asn-Tyr-Cys20-Asn-Val-Pro; and B-chain, Ala-Val-Leu-Asn-Gln-His-Leu-Cys-Gly-Ser10-His-Leu-Val- Glu- Ala-Leu-Tyr-Leu-Val-Cys20-Ala-Asp-Asn-Gly-Phe- Phe-Tyr-Lys-Pro-Ser30-Gly. Lungfish insulin contains unusual structural features, such as the dipeptide extension to the C-terminus of the A-chain and the substitution Arg --> Asn at position B-23 in the putative receptor binding region of insulin, which may be expected to influence appreciably its biological potency relative to mammalian insulins. Lungfish insulin also contains amino acid substitutions such as Gly --> Ala at position B-21, Glu --> Asp at position B-22, and a Lys --> Ser residue at position B-30, previously found in insulins from amphibia. This observation is consistent with paleontological data suggesting that lungfish and amphibia share a close phylogenetic relationship.

Characterization of the pancreatic hormones from the Brockmann body of the tilapia: implications for islet xenograft studies

The Brockmann body of the teleost fish, the tilapia (Oreochromis nilotica) has been considered as a potential source of islet xenograft tissue for patients with insulin-dependent diabetes. This study describes the purification from an extract of tilapia Brockmann bodies of insulin and several peptides arising from different pathways of post-translational processing of two proglucagons, two prosomatostatins and proPYY. The primary structure of tilapia insulin is similar to insulins from other teleosts (particularly the anglerfish, Lophius americanus) except that the strongly conserved glutamine residue at position 5 in the A-chain, a residue that is important in the binding of insulin to its receptor, is replaced by glutamic acid. In common with other teleosts, the tilapia Brockmann body expresses two non-allelic glucagon genes. Alternative pathways of post-translational processing lead to glucagons with 29 and 36 amino acid residues derived from proglucagon I and glucagons with 29 and 32 residues derived from proglucagon II. Glucagon-like peptides with 30 and 34 residues derived from proglucagon II were also isolated. In each case, the longer peptide is a C-terminally extended form of the shorter. Tilapia peptide tyrosine-tyrosine (PYY) was isolated in a C-terminally alpha-amidated from with 36 amino acid residues that is structurally similar (89% sequence identity) to anglerfish PYY. A 30-amino acid peptide, representing the C-terminal flanking peptide of PYY, was also isolated that shows only 53% sequence identity with the corresponding anglerfish peptide. Tilapia somatostatin-14 is identical to mammalian somatostatin but the [Tyr7, Gly10] somatostatin-containing peptide derived from prosomatostatin II contains the additional substitution (Phe11-->Leu) compared with the corresponding peptide from other teleosts.

Purification and structural characterization of insulin from a caecilian, Typhlonectes natans (Amphibia: Gymnophiona)

Despite the important position of amphibia in phylogeny, efforts at the structural characterization of amphibian neurohormonal peptides have largely been confined to the Anurans (frogs and toads). Insulin was purified from an extract of the pancreas of the caecilian, Typhlonectes natans. The primary structure of the peptide was established as: [formula: see text] This amino acid sequence contains several unusual substitutions (Gln-->Lys at A5, His-->Leu at A8, Gln-->Glu at A15, and Gly -->Ala at B20) that are not present in other amphibian insulins. The structure of insulin appears to be less well conserved among the different orders of amphibia, compared with reptiles and birds.

Identification of insulin-like peptides in cerebral ganglia neurosecretory cells of the mussel Mytilus edulis

The immunostaining patterns of cerebral ganglia sections from the mussel Mytilus edulis with monoclonal antibodies raised against cerebral ganglia (CG) extracts were compared to those obtained with various polyclonal anti-insulin-like antibodies. One of the monoclonal antibodies (MAB 46) revealed clusters of positive cells in localization comparable to those revealed by the polyclonal antibodies. The nature of the antigen recognized by MAB 46 and the polyclonal antibodies was compared by gel filtration-HPLC of a cerebral ganglia extract. Similar peaks were revealed by the monoclonal and polyclonal antibodies. MAB 46 significantly inhibited the cerebral ganglia induced stimulation of amino-acid incorporation by mantle edge cell suspensions, suggesting that the antigen recognized by MAB 46 is involved in the control of growth.

Peptides related to insulin-like growth factor 1 in the gastro-entero-pancreatic system of bony and cartilaginous fish

Evidence for the presence of peptides, related to insulin-like growth factor 1 (IGF-1) has been obtained in serum and various organs of representatives of osteichthyes and chondrichthyes, i.e., the bony fish Myoxocephalus (Cottus) scorpius and the cartilaginous fish Raja clavata. The peptides were identified by means of gel chromatography and an IGF-1 radioimmunoassay. IGF-1-like immunoreactivity was detected in three different apparent molecular mass forms, i.e., 17 kDa, 6 kDa and 4 kDa, the occurrence of which seemed to depend on the species. When the same antiserum was used immunohistochemically, IGF-1-like immunoreactivity was observed in endocrine cells of the open type in the intestinal mucosal epithelium. These cells exhibited distinct and species-specific distribution patterns. Endocrine cells of the pancreas as well as epithelial cells of the pancreatic duct also showed IGF-1-like immunoreactivity. Occasionally, IGF-1-like immunoreactivity was observed also in interstitial cells. The distribution patterns and densities of the IGF-like immunoreactive cells correlated with the results obtained by radioimmunoassay of the crude extracts. Absorption studies indicated that the IGF-1-like peptides observed differ from mammalian and submammalian insulins as well as from mammalian IGF-1.

Presence of IGF-1-like peptides in the neuroendocrine system of the Atlantic hagfish, Myxine glutinosa (Cyclostomata): evidence derived by chromatography, radioimmunoassay and immunohistochemistry

By the use of radioimmunoassay and chromatography peptides related to insulin-like growth factor 1 (IGF-1) have been identified in the cylostomian species Myxine glutinosa. IGF-1-like-immunoreactivity was detected in serum as well as in brain, intestine, pancreas and liver. After acid gel chromatography, the IGF-1-like immunoreactivity eluted as one major peak, with an apparent molecular weight of between 2-4 kDa. When the same antiserum was applied immunohistochemically, IGF-1-like-immunoreactivity was observed in endocrine cells of the mucosal epithelium throughout the primitive intestinal tube. These cells were of the open type and occurred in small clusters. In addition, the majority of the endocrine cells of the pancreas of Myxine displayed IGF-1-like-immunoreactivity. In some of the specimens investigated IGF-1-like-immunoreactive perikarya and fibers were observed on all levels of the brain. Distribution patterns and densities of the IGF-1-like-immunoreactive structures in Myxine correlated with the measurements obtained by radioimmunoassay. Absorption studies with insulin- and IGF-related peptides as well as with crude extracts and the peak material obtained after gel chromatography indicated that the IGF-1-like peptides in Myxine are different from mammalian and non-mammalian insulins as well as from mammalian IGF-1. Generally, the results suggest a long phylogenetic history of IGF-1-like peptides and indicate their fundamental functional impact in all vertebrates.

Structure and receptor-binding activity of insulin from a holostean fish, the bowfin (Amia calva)

The holostean fishes are the extant representatives of the primitive ray-finned fishes from which the present-day teleosts may have evolved. The primary structure of insulin from a holostean fish, the bowfin (Amia calva), was established as: A-chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Leu-Lys-Pro-Cys-Thr-Ile-Tyr-Glu-Met-Glu- Lys-Tyr-Cys-Asn B-chain: Ala-Ala-Ser-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala-Leu-Phe-Leu- Val-Cys-Gly-Glu-Ser-Gly-Phe-Phe-Tyr-Asn-Pro-Asn-Lys-Ser This amino acid sequence contains several substitutions (methionine at A16, phenylalanine at B16 and serine at B22) at sites that have been strongly conserved in other vertebrate species and that may be expected to influence biological activity. Consistent with this prediction, bowfin insulin was approx. 14-fold less potent than pig insulin in inhibiting the binding of [125I-Tyr-A14](human insulin) to transfected mouse NIH 3T3 cells expressing the human insulin receptor.

Primary structure of gonadotropin-releasing hormone from the brain of a holocephalan (ratfish: Hydrolagus colliei)

Gonadotropin-releasing hormone (GnRH) in the ratfish brain has been isolated and purified using reverse-phase high performance liquid chromatography. Amino acid composition and sequence analysis indicate that the primary structure is pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The presence of the amino terminal pyroglutamic acid has been confirmed by degradation studies with pyroglutamyl aminopeptidase. The amidated carboxy terminus and molecular weight were confirmed using mass spectrometry. Moreover, sequence comparison and coelution studies with one of the synthetic forms of GnRH (chicken GnRH II) indicate that the ratfish and chicken GnRH II molecules are identical. This represents the first sequence data of a GnRH molecule from a cartilaginous fish (class: Chondrichthyes). It is argued that the ratfish GnRH molecule has been retained for over 400 million years of evolution and is expressed in most vertebrate classes.

Isolation and structural characterization of insulin and glucagon from the holocephalan species Callorhynchus milii (elephantfish)

Both insulin and glucagon from the pancreas of the holocephalan cartilaginous fish Callorhynchus milii (elephantfish) have been isolated and purified. Two reverse-phase h.p.l.c. steps enabled recovery of sufficient material for gas-phase sequencing of the intact chains as well as peptide digestion products. The elephantfish insulin sequence shows 14 differences from pig insulin, including two unusual substitutions, Val-A14 and Gln-B30, though none of these is thought likely to influence receptor binding significantly. The insulin B-chain contains 31 residues, one more than mammalian insulins, but markedly less than that of the closely related ratfish with which it otherwise exhibits high sequence similarity. Elephantfish and pig glucagons differ at only four positions, but there are six changes from the ratfish glucagon-36 (normal glucagon contains 29 residues) sequence. It is apparent that different prohormone proteolytic processing mechanisms operate in the two holocephalan species.

Purification of a marsupial insulin: amino-acid sequence of insulin from the eastern grey kangaroo Macropus giganteus

Insulin has been purified from kangaroo pancreas by acidic ethanol extraction, diethyl ether precipitation and gel filtration. The amino-acid sequence of this, the first marsupial insulin to be studied, is reported. It differs from human insulin by only four amino-acid substitutions, all in regions of the molecule previously known to be variable. However, it should be noted that one of these, asparagine for threonine at A8, has not been reported before. Computer comparisons of all 43 insulin sequences reported to date with kangaroo insulin show it to be most closely related to a group of mammalian insulins (dog, pig, cow, human) known to be of high biological potency. The measurement of blood glucose lowering in the rabbit by kangaroo insulin is consistent with this conclusion. Comparisons of amino-acid sequences of other proteins with their kangaroo counterparts show a greater difference, in line with the time of divergence of marsupials. The limited differences observed in insulin and cytochrome c suggest that their structures need to be closely conserved in order to maintain function.

Multiple molecular forms of insulin and glucagon-like peptide from the Pacific ratfish (Hydrolagus colliei)

The primary structure of an insulin isolated from the pancreas of the holocephalan fish, Hydrolagus colliei (Pacific ratfish), has been established as A-chain: GIVEQCCHNTCSLANLEGYCN B-chain: VPTQRLCGSHLVDALYFVCGERGFFYSPKPIRELEPLL. Three further molecular forms of insulin were also isolated and shown to have the same A-chain but truncated B-chains of 31-, 36-, and 37-amino acid residues. It is proposed that all four insulins arise from a single proinsulin by proteolytic cleavages at different sites within the C-peptide region. The insulin with 38 amino acids in the B-chain was equipotent with human insulin in inhibiting the binding of radiolabelled human insulin to rat fat cells but the maximum effect of ratfish insulin upon the transport of 3-O-methylglucose into the cells was only 65% of the maximum effect of human insulin. Two molecular forms of glucagon-like peptide were isolated from the ratfish pancreas. The primary structure of the more abundant peptide was established as HADGIYTSDVASLTDYLKSKRFVESLSNYNRKQND. The primary structure of the second peptide was the same except that it was extended from the C-terminus by the sequence RRM. It is probable, therefore, that both glucagon-like peptides also arise from a single proglucagon by different pathways of post-translational processing.

Isolation of the tachykinin, des[Ser1Pro2]scyliorhinin II from the intestine of the ray, Torpedo marmorata

A peptide with neurokinin A-like immunoreactivity was isolated from an extract of the intestine of an elasmobranch fish, Torpedo marmorata. The primary structure of the peptide was established as Ser-Asn-Ser-Lys-Cys-Pro-Asp-Gly-Pro-Asp-Cys-Phe-Val-Gly-Leu-Met.NH2. This amino acid sequence is identical to that of residues (3-18) of scyliorhinin II previously isolated from the intestine of the common dogfish (Scyliorhinus canicula). The presence of the truncated peptide, lacking Ser-Pro, in the Torpedo gut suggests that scyliorhinin II may be a substrate for an enzyme with dipeptidylpeptidase IV-like specificity. The data support previous assertions that strong evolutionary pressure has acted within the elasmobranch subclass of chondrichthyean fish to conserve the structures of regulatory peptides.

Isolation and structure of lamprey (Petromyzon marinus) insulin

Insulin has been purified to homogeneity from the caudal and cranial pancreas of the adult sea lamprey (Petromyzon marinus). The final yield was 18.6 nmol/g (127.8 micrograms/g). The structures of both A- and B-chains have been determined using amino acid analyses, gas-phase sequence analyses, and proteolytic mapping by fast atom bombardment-mass spectrometry. The sequence of the A-chain was found to be GIVEQCCHRKCSIYDMENYCN. The sequence of the B-chain, extended at the amino terminus, was determined to be SALT-GAGGTHLCGSHLVEALYVVCGDRGFFYTPSKT. Lamprey insulin retains the common features of vertebrate insulins. Sea lamprey insulin has no more homology to hagfish (Myxine glutinosa) insulin than it has to the teleost fish or to mammalian insulins.

Primary structure of insulin and glucagon from the flounder (Platichthys flesus)

Insulin and glucagon have been isolated from the Brockmann bodies of the flounder, a teleostean fish, and their primary structures established by automated Edman degradation. The A-chain of flounder insulin shows strong homology to the A-chains from the coho salmon (Oncorhynchus kisutch; 100%) and the anglerfish (Lophius americanus; 95%) but homologies in the B-chain region are weaker (salmon 79%, anglerfish 83%). Flounder insulin B-chain contains the novel sequence Val-Val-Pro-Pro at the NH2 terminus and the highly conserved seryl residue at position 10 (B 9 in mammals) is replaced by an alanyl residue. Flounder glucagon is identical to anglerfish glucagon II but shows four amino acid substitutions compared with salmon glucagon.

The primary structure of ratfish insulin reveals an unusual mode of proinsulin processing

The primary structure of insulin from the Holocephalan fish, Hydrolagus colliei (the ratfish), has been established by automated Edman degradation as: (Formula: see text). The presence of a COOH-terminal extension to the B-chain is consistent with the occurrence of a single base mutation in the region of the gene encoding one of the dibasic residue processing sites [Arg31(AGA)----Ile* (AUA)] with the result that the ratfish has utilised an alternative cleavage site within the C-peptide region of proinsulin.

Primary structure of insulin and a truncated C-peptide from an elasmobranchian fish, Torpedo marmorata

Insulin has been isolated from the pancreas of Torpedo marmorata, an elasmobranchian fish, and shown to contain 21 amino acid residues in the A-chain and 30 residues in the B-chain. The sequence of insulin has been strongly conserved within the class Elasmobranchii with only one substitution and one deletion in the A chain and one substitution in the B-chain compared with insulin from the spiny dogfish, Squalus acanthias. A second peptide, present in the pancreatic extracts in approximately equimolar concentration with insulin, was identified as a heptadecapeptide. The sequence of this peptide shows homology to the N-terminal region of anglerfish (Lophius americanus) C-peptide at six of 17 sites. The isolation of a truncated C-peptide suggests either that the sequence encoding the COOH-terminal region of T. marmorata C-peptide has been deleted from the preproinsulin gene or that a larger C-peptide has undergone a proteolytic cleavage in the central portion of the molecule during packaging in the secretory granules of the B cell.

Coypu insulin. Primary structure, conformation and biological properties of a hystricomorph rodent insulin

Insulin from a hystricomorph rodent, coypu (Myocaster coypus), was isolated and purified to near homogeneity. Like the other insulins that have been characterized in this Suborder of Rodentia, coypu insulin also exhibits a very low (3%) biological potency, relative to pig insulin, on lipogenesis in isolated rat fat-cells. The receptor-binding affinity is significantly higher (5-8%) in rat fat-cells, in rat liver plasma membranes and in pig liver cells, indicating that the efficacy of coypu insulin on receptors is about 2-fold lower than that of pig insulin. The primary structures of the oxidized A- and B-chains were determined, and our sequence analysis confirms a previous report [Smith (1972) Diabetes 21, Suppl. 2, 457-460] that the C-terminus of the A-chain is extended by a single residue (i.e. aspartate-A22), in contrast with most other insulin sequences, which terminate at residue A21. In spite of a large number of amino acid substitutions (relative to mammalian insulins), computer-graphics model-building studies suggest a similar spatial arrangement for coypu insulin to that for pig insulin. The substitution of the zinc-co-ordinating site (B10-His----Gln) along with various substitutions on the intermolecular surfaces involved in the formation of higher aggregates are consistent with the observation that this insulin is predominantly 'monomeric' in nature. The c.d. spectrum of coypu insulin is relatively similar to those of casiragua insulin and of bovine insulin at low concentration.

The isolation, purification and amino-acid sequence of insulin from the teleost fish Cottus scorpius (daddy sculpin)

Insulin from the principal islets of the teleost fish, Cottus scorpius (daddy sculpin), has been isolated and sequenced. Purification involved acid/alcohol extraction, gel filtration, and reverse-phase high-performance liquid chromatography to yield nearly 1 mg pure insulin/g wet weight islet tissue. Biological potency was estimated as 40% compared to porcine insulin. The sculpin insulin crystallised in the absence of zinc ions although zinc is known to be present in the islets in significant amounts. Two other hormones, glucagon and pancreatic polypeptide, were copurified with the insulin, and an N-terminal sequence for pancreatic polypeptide was determined. The primary structure of sculpin insulin shows a number of sequence changes unique so far amongst teleost fish. These changes occur at A14 (Arg), A15 (Val), and B2 (Asp). The B chain contains 29 amino acids and there is no N-terminal extension as seen with several other fish. Presumably as a result of the amino acid substitutions, sculpin insulin does not readily form crystals containing zinc-insulin hexamers, despite the presence of the coordinating B10 His.

Characterization of cat insulin

Cat insulin was isolated and both chains were characterized by determination of the primary structures. The molecule was found to differ from human insulin at four positions, A8 (Ala), A10 (Val), A18 (His), and B30 (Ala). A comparison with other known insulin structures suggests that cat insulin has an uncommon property: it appears to be the only insulin found so far with His at position A18. The difference is compatible with a conserved overall conformation but this histidine occupies a position close to the suggested receptor interacting area and may influence some binding properties.

Characterization of coho salmon (Oncorhynchus kisutch) insulin

Insulin has been isolated from islet tissue of coho salmon (Oncorhynchus kisutch) by gel filtration and HPLC and the complete amino acid sequence has been determined. The sequence differs from bovine insulin at 14 sites but all interchanges are conservative from the viewpoint of preservation of conformation. A comparison of insulin sequences from other fish is presented. Salmon insulin cross-reacts very weakly with antiserum to bovine insulin and vice versa. A completely homologous radioimmunoassay has been developed and used to estimate the insulin in salmon islet tissue and in plasma. The hypoglycemic effect of salmon insulin in salmon was more pronounced and persisted longer than that caused by identical doses of bovine insulin.

Phylogenetical aspects on islet hormone families: a minireview with particular reference to insulin as a growth factor and to the phylogeny of PYY and NPY immunoreactive cells and nerves in the endocrine and exocrine pancreas

A common feature in the phylogeny of the four islet hormones (insulin, somatostatin, glucagon, PP) is that they do not seem to occur in the most primitive metazoan animals investigated so far, namely the coelenterates. However, already in the earliest protostomian invertebrates, such as flatworms and annelids, somatostatin and PP immunoreactive nerve fibres were found. In highly developed forms of protostomian invertebrates, such as insects, all the four islet hormones are represented as immunoreactive nerve cells and nerve fibres in the brain. In deuterostomian invertebrates a brain-gut-axis has evolved as regards somatostatin and PP, whereas insulin and glucagon now seem to occur exclusively as cells of open type in the gut mucosa. This brain-gut-axis for somatostatin and PP persists in all the vertebrates. The insulin cells, however, leave the gut mucosa already in the earliest forms of vertebrates and then appear only as cells in the islet parenchyma and in the mucosa of the bile duct (Agnatha) or in the pancreatic ducts (Gnathostomi). To some extent, glucagon islet cells evolve in a similar manner; here, however, cells immunoreactive with the precursor hormone, glicentin (enteroglucagon), persist in the gastrointestinal tract mucosa. A few PYY immunoreactive cells have been found in the pancreatic islet parenchyma of reptiles and mammals, often as disseminated cells in the acinar tissue. In the pancreas of these phyla NPY only occurs in neurons and nerve fibres. In pilot studies the effects of hagfish insulin as a growth factor have been compared with those of pig insulin on Swiss 3T3 mouse embryonic fibroblasts.

Biochemical and physiological studies on peptides from the elasmobranch gut

A peptide fraction has been purified from intestinal extracts of the dogfish Scyliorhinus canicula which is a powerful stimulant of rectal gland secretory activity. This peptide is distinct from elasmobranch vasoactive intestinal polypeptide (VIP). The elasmobranch VIP fraction is not active in the rectal gland assay and mammalian VIP is only an effective agonist in Squalus and not in Scyliorhinus or Raja. Preliminary characterisation of the elasmobranch VIP indicate that it has strong N-terminal similarities with mammalian VIP but has limited C-terminal comparability. It is suggested that the rectal gland stimulating peptide, rectin, rather than VIP is responsible for the control of fluid and electrolyte secretion of elasmobranchs.

The relative effects of different types of growth factors on DNA replication, mitosis, and cellular enlargement

It was recently demonstrated that growth in cell size can be dissociated from DNA synthesis and mitosis. 3T3 cells starved to quiescence in low serum concentration can be stimulated to undergo DNA synthesis and one cell division without growing in size (unbalanced growth) (42-44). We report here that in cells stimulated to undergo unbalanced growth, the cell nucleus undergoes balanced growth, i.e., nearly doubles in size prior to mitosis. The reduced ability to grow in cell size under unbalanced growth conditions is thus mainly ascribable to the cytoplasm. Furthermore, the extent to which cells grow in size prior to mitosis is dependent on the serum concentration in the tissue culture medium (44). This data suggests that some macromolecular factor or factors in serum are required for growth in cell size prior to mitosis. We report in this study that epidermal growth factor (EGF) alone exerts a small but significant stimulatory influence on DNA synthesis and mitosis but does not affect cellular enlargement. In contrast, insulin added at supraphysiological concentrations does not stimulate quiescent cells to enter S phase but instead stimulates growth in cell size in the small fraction of dividing cells. Furthermore, cells stimulated to proliferate by EGF could be induced to undergo balanced growth when insulin was added concomitantly. Finally, platelet-derived growth factor (PDGF) stimulates quiescent sparse 3T3 cells to undergo DNA synthesis and mitosis. PDGF also exerts a limited but significant effect on cellular enlargement. However, PDGF alone could not induce a complete balanced growth, i.e., a doubling in cell size prior to mitosis.

Amino-terminal variation in melanoma antigens

Melanoma tumors express both common antigenic determinants and individually specific markers. A melanoma-specific glycoprotein antigen ( B700 ) with a molecular weight of approximately 65,000 daltons was detected on murine B16 melanoma cells but appears on other murine and human melanoma tumors. In order to determine the relationship between the B700 antigen and other melanoma antigens which have been described and to elucidate molecular changes that have taken place in the transformation from melanocyte to melanoma, we have purified the B700 glycoprotein to homogeneity. We have carried out amino acid composition analysis and partial sequence determinations and report that the B700 melanoma antigen shows similarities to serum albumin, but is not identical to this normal component. Moreover, amino-terminal variation occurs in the first 15 residues of the B700 antigen produced by separate B16 tumors.