Peptides ejection

Figure 7.4 is a photograph of a portion of the peptide controls slide printer. A stack of microscope slides, ready for printing, is at the far left. The slides are automatically ejected from the stack, one at a time. The slides are moved on a conveyer to the right, positioning them under the print head. The print head has eight nozzles, out of which microliter-sized droplets are ejected onto an underlying slide. The slide conveyer then places a new slide under the nozzles, and the process repeats. 

FIGURE 7.34 Decomposition of the symmetrical anhydride of A-methoxycarbonyl-valine (R1 = CH3) in basic media.2 (A) The anhydride is in equilibrium with the acid anion and the 2-alkoxy-5(4//)-oxazolone. (B) The anhydride undergoes intramolecular acyl transfer to the urethane nitrogen, producing thelV.AT-fcwmethoxycarbonyldipeptide. (A) and (B) are initiated by proton abstraction. Double insertion of glycine can be explained by aminolysis of the AA -diprotected peptide that is activated by conversion to anhydride Moc-Gly-(Moc)Gly-0-Gly-Moc by reaction with the oxazolone. (C) The A,A -diacylated peptide eventually cyclizes to the IV.AT-disubstituted hydantoin as it ejects methoxy anion or (D) releases methoxycarbonyl from the peptide bond leading to formation of the -substituted dipeptide ester. 

The use of TFA as a mobile-phase additive in LC-MS can be problematical when using electrospray ionization. In negative ion detection, the high concentration of TFA anion can suppress analyte ionization. In positive ion detection, TFA forms such strong ion pairs with peptides that ejection of peptide pseudo-molecular ions into the gas phase is suppressed. This problem can be alleviated by postcolumn addition of a weaker, less volatile acid such as propionic acid.14 This TFA fix allows TFA to be used with electrospray sources interfaced with quadrupole MS systems. A more convenient solution to the TFA problem in LC-MS is to simply replace TFA with acetic or formic acid. Several reversed-phase columns are commercially available that have sufficient phase coverage and reduced levels of active silanols such that they provide satisfactory peptide peak shapes using the weaker organic acid additives.15... 

Oxytocin, a nine amino acid peptide, is synthesized primarily in the paraventricular and supraoptic (SON) nuclei of the hypothalamus, from which it is released to the general circulation through the posterior pituitary (Insel et ah, 1997). However, oxytocinergic fibers have also been found to project from the PVN to the limbic system and several autonomic centers in the brain stem. This central OT pool appears to be independent of pituitary OT release cerebrospinal fluid (CSF) and plasma OT responses to numerous stimuli are not correlated (Insel, 1997). Oxytocin and its analog (or partner) peptide vasopressin are found only in mammals. A related peptide, vasotocin, thought to be the evolutionary precedent of these peptides, is found in reptiles and birds. The first known actions of OT were its peripheral effects on the physiology of new mothers. In mammals, OT stimulates milk ejection and uterine contraction, essential aspects of maternal physiology (Insel et ah, 1997). 

Oxytocin (OT) is a nonapeptide in which six amino acids form a ring closed by a disulfide bridge, while the ring itself forms an antiparallel pleated sheet. The tail portion of the peptide, composed of Pro-Leu-Gly-NHj, is also rigidly held in a folded conformation. Oxytocin causes the powerful contraction of some smooth muscles and plays a vital role in milk ejection (not to be confused with milk secretion, which is regulated by prolactin). It also has uterotonic action, contracting the muscles of the uterus, and is therefore used clinically to induce childbirth. 

Oxytocin is a peptide hormone secreted by the posterior pituitary that participates in labor and delivery and elicits milk ejection in lactating women. During the second half of pregnancy, uterine smooth muscle shows an increase in the expression of oxytocin receptors and becomes increasingly sensitive to the stimulant action of endogenous oxytocin. Pharmacologic concentrations of oxytocin powerfully stimulate uterine contraction. 

Impaired milk ejection may respond to nasal oxytocin. Synthetic peptide and nonpeptide oxytocin antagonists that can prevent premature labor are being investigated. 

Ideally biomarkers of activity should be identified at various times over the course of the study to support the pharmacodynamic activity (e.g., normalization of insulin, improvement in beta cell function as measured by C-peptide level, or control of glucose following transplantation of P pancreatic islet cells) improvement of motor coordination in mice with spinal cord damage following transplant of neurons or repair of heart function (e.g., functional measures such as LV ejection fraction, pressure volume loops, ventricular pressure and heart wall thickness). Such markers may also be useful in subsequent clinical... 

Oxytocin in a nine amino acid peptide that is synthesized in hypothalamic neurons and transported down through axons of the posterior pituitary for secretion into blood. Oxytocin has three major physiological effects stimulation of miUc ejection, stimulation of uterine smooth muscle contraction at birth, and establishment of maternal behavior. 

Chemical, electron field desorption, laser desorption, photon, plasma desorption, spark, and thermal ionization are all used as primary ionization processes. Secondary ionization is the term used to describe a process in which ions are ejected from a surface as a result of bombardment by a primary beam of atoms or ions. If low energy or soft ionization techniques are used, the mass of the target molecule can be determined. Advances in soft ionization techniques have extended the use of MS to the direct measurement of peptide and protein mass. Ionization at higher energy results in more extensive fragmentation of target molecules. 

Type 1 question regarding diagnostic accuracy of a test In patients coming to the emergency department with shortness of breath, how well does B-type natriuretic peptide (BNP) or N-terminal pro-BNP predict (identify the presence of) heart failure as assessed by the cardiac ejection fraction measured by echocardiography ... 

Richards AM, Nicholls MG, Espiner EA, Lainchbury JG, Troughton RW, Elliott J, et al. B-type natriuretic peptides and ejection fraction for prognosis after myocardial infarction. Circulation 2003 107 2786-92. 

Charge loss (peptide and protein loses one charge and the ejected ion has one charge)... 

Figure 9 Illustration of the 1/3rd rule. The top panel shows multiple charge states of the phosphopantetheinylated active site containing peptide from PKS LovB. The 16+ ion at 854.636m/z and the 15+ ion at 911.636mlz of the peptide were subjected to CID. The middle panel shows that PPant ejection (261 m/z) is clearly detected in the MS/MS or MS2 spectrum resulting from CID of the 16+ ion. The bottom panel shows that PPant ejection resulting from fragmentation of the 15+ ion cannot be detected due to limitations defined by the 1/3rd rule.

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