Glutamic Acid In Position Research Articles

Interaction of Peptides Related to Secretin with Hormone Receptors on Pancreatic Acinar Cells

Three analogues of the carboxyl-terminal tricosapeptide of secretin (S5-27), one with glutamine replacing glutamic acid in position 9 (9-Gln-S5-27), a second with asparagine substituted for aspartic acid in position 15 (15-Asn-S5-27), and a third with both replacements (9-Gln-15-Asn-S5-27) were tested for their ability to interact with hormone receptors on dispersed pancreatic acinar cells. Each of these analogues inhibited binding of 125I-labeled vasoactive intestinal peptide (VIP). None of the analogues increased cellular cyclic AMP but each inhibited the increase in cellular cyclic AMP produced by secretin or VIP. At the high affinity VIP receptor (the low affinity secretin receptor) each analogue had an apparent affinity which was greater than that for S5-27, whereas at he low affinity VIP receptor (the high affinity secretin receptor), each of the analogues had an apparent affinity which was the same as that for S5-27. Thus, in S5-27, substituting glutamine in position 9 or asparagine in position 15 makes the fragment more VIP-like but not less secretin-like. These results also provide additional evidence that the receptor having a low affinity for secretin and a high affinity for VIP is functionally distinct from the receptor having a high affinity for secretin and a low affinity for VIP.

Molecular Aspects of Sickle Cell Disease

AbstractSickle cell hemoglobin (hemoglobin S) contains valine instead of glutamic acid in position 6 of the β‐chain. Few detectable conformational differences exist between hemoglobin S and normal adult hemoglobin (hemoglobin A). Following loss of oxygen, sickle cell hemoglobin (hemoglobin S) self associates to form a liquid crystal phase which distorts the erythrocyte into the sickle shape thereby resulting in the clinical symptomology associated with sickle cell anemia. This gel contains deoxyhemoglobin S monomers and polymers in equilibrium. The polymerization process is known to have a negative temperature coefficient, to be pH dependent, and to be extremely dependent on hemoglobin S concentration. The polymerization of deoxyhemoglobin S appears to be entropically driven and occurs in two kinetic phases, a delay period and a rapid polymerization process. The polymer consists of tubules containing six or eight strands of deoxyhemoglobin S tetramers which align with one another. Each strand is would around the tubule with a pitch of about 3000 Å, but the precise nature of the intermolecular hemoglobin S contacts is not known. Subsequent alignment of the tubules occurs and results in the tactoids observed in (S/S) erythrocytes. While many of the details of polymer formation and structure remain to be elucidated, several attempts to chemically alter the sickling phenomenon have been carried out. As yet, however, no satisfactory chemical treatment has been discovered.

Studies on the conformation of secretin: The position of the helical stretch

An analog of the C-terminal tricosapeptide of secretin, with aspartic acid replacing glutamic acid in position 9 and lysine substituted for arginine in position 21, was prepared. The synthesis was carried out in solution by stepwise chain lengthening with the application of the in situ technique. The ord-cd spectra of this new analog closely resemble the spectra of the tricosapeptide with the unaltered secretin sequence and of the analog in which only arginine-21 was replaced by lysine and of secretin itself. The incorporation of aspartic acid instead of glutamic acid-9 resulted in an N-terminal sequence that has a consïderably reduced probability of assuming a helical conformation. The observation that the helix content remained unchanged adds support to a model of secretin in which the helical stretch is near the C-terminus. The role of an acidic residue in position 9 is also discussed.

The amino-terminal sequence of the VHIII subgroup of pooled porcine IgG.

Pig gamma-chains contain a significant fraction of the unblocked VHIII variable region subgroup. The amino terminal sequence (30 residues) was found to be uniform and more than 90% homologous with the prototype sequence of the human VHIII subgroup. An additional VHIII phylogenetically associated residue, glutamic acid in position 2 was identified in these porcine heavy chains.

Hemoglobin Rush [β101 (G3) Glutamine]: A New Unstable Hemoglobin Causing Mild Hemolytic Anemia

Abstract A mild hemolytic anemia in a 43-yr-old black woman was attributed to the presence of an abnormal hemoglobin (Hb Rush) which migrated cathodically to Hb A at pH 8.0. Its structural abnormality was found to be in the β-chain, β101 (G3) glu → gln. Another electrophoretic band at pH 8.0 proved to be a hybrid tetramer (αA2βAβRush). Hb Rush is heat unstable. A likely explanation of the instability is the presence of an uncovered positive charge in the central cavity where normally glutamic acid in position 101 neutralizes arginine in position 104 contributing to the net neutrality in this region. This neutrality is disturbed by the substitution of glutamic acid by glutamine in Hb Rush.

Relation between structure and function in some partially synthetic ribonucleases S′. I. Kinetic determinations

For a better understanding of the structure—function relationships in the ribonuclease molecule, detailed kinetic studies have been carried out on partially synthetic ribonucleases in which some amino acid residues were substituted or deleted. The following ribonuclease S′ analogs have been examined: [Orn 10]-ribonuclease S′; des-Lys 1-[Orn 10]-ribonuclease S′; des-Lys 1, Glu 2-[Orn 10]-ribonuclease S′; des-Lys 1, Glu 2, Thr 3-[Orn 10]-ribonuclease S′ and [Pro 6, Orn 10]-ribonuclease S′. In order to regenerate the arginyl residue, which is present in position 10 in the natural sequence, the S-peptide analogs belonging to the [Orn 10]-series were transformed into the corresponding guanidinated derivatives by treatment with O-methylisourea. The activation curves of the S-protein with varying amounts of the S-peptide analog, before and after guanidination, against different substrates have been determined. Moreover, the kinetic parameters of the modified enzymes obtained by mixing S-protein with different S-peptide analogs were calculated. The hypothesis of the existance of an interaction between the γ-carboxyl group of glutamic acid in position 2 in the S-peptide sequence and the guanidinium group of arginine in position 10 has found experimental support. The absence of this interaction, which probably stabilizes the conformation of the N-terminal sequence of the enzyme, brings about some conformational changes on the active center region.

Relationships between the structure and biological activities of corticotropin and related peptides

The relationship of the structure of corticotropin to its biological activities has been investigated by studies on the adrenal and extra-adrenal effects of a number of modified and synthetic corticotropins. The adrenal effects studied were in vivo and in vitro adrenal steroidogenesis. The extra-adrenal effects investigated were in vivo and in vitro adipokinetic activities and in vivo hypoglycemic activity. The structural alterations were: (1) alterations in the N-terminal serine, (2) changes in the chain length, (3) blockage of certain active groups and, (4) changes in the internal structure of the polypeptide chain. The studies with several modified corticotropins in which the N-terminal serine was altered revealed that a free N-terminal α amino group was necessary for full in vivo adrenal-stimulating activity. Destruction of the α amino group caused a dissociation of in vivo adrenal and extra-adrenal activities, while blockage of it by N-acetylation markedly reduced all activities. The minimal chain length which carried the full in vivo adrenal and extra-adrenal activity of the molecule was that comprising the N-terminal 20 amino acid residues. Blockage of several active groups in the molecule (acetylation of the free α amino group of serine, formylation of the ∈ amino groups of all the lysines and conversion of glutamic acid in position 5 to glutamirie) caused hyperglycemia in mice rather than the expected hypoglycemia. Replacement of the methionine in position 4 by an α amino-butyryl group only modestly reduced activity. The significance of these findings in terms of the relationship of corticotropin structure to adrenal and extra-adrenal activities is discussed. The relationship of the structure of corticotropin to its biological activities has been investigated by studies on the adrenal and extra-adrenal effects of a number of modified and synthetic corticotropins. The adrenal effects studied were in vivo and in vitro adrenal steroidogenesis. The extra-adrenal effects investigated were in vivo and in vitro adipokinetic activities and in vivo hypoglycemic activity. The structural alterations were: (1) alterations in the N-terminal serine, (2) changes in the chain length, (3) blockage of certain active groups and, (4) changes in the internal structure of the polypeptide chain. The studies with several modified corticotropins in which the N-terminal serine was altered revealed that a free N-terminal α amino group was necessary for full in vivo adrenal-stimulating activity. Destruction of the α amino group caused a dissociation of in vivo adrenal and extra-adrenal activities, while blockage of it by N-acetylation markedly reduced all activities. The minimal chain length which carried the full in vivo adrenal and extra-adrenal activity of the molecule was that comprising the N-terminal 20 amino acid residues. Blockage of several active groups in the molecule (acetylation of the free α amino group of serine, formylation of the ∈ amino groups of all the lysines and conversion of glutamic acid in position 5 to glutamirie) caused hyperglycemia in mice rather than the expected hypoglycemia. Replacement of the methionine in position 4 by an α amino-butyryl group only modestly reduced activity. The significance of these findings in terms of the relationship of corticotropin structure to adrenal and extra-adrenal activities is discussed.