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The marine mollusc Aplysia produces an egg-laying hormone (ELH), which induces ovulation and acts on central neurons to effect egg-laying behavior. ELH is synthesized in the neuroendocrine bag cells; it is encoded by the ELH gene, one of a small family of genes, each of which is expressed in a tissue-specific manner. We review what is known about post-translational processing of the ELH precursor, and report the isolation and chemical characterization of [epsilon]-bag-cell peptide, the seventh peptide product of the ELH precursor to be identified to date. Amino acid compositional and sequence analyses demonstrated that the primary structure of the 19-residue peptide is: [NH.sub.2]-Ser-Val-Leu-Thr-Pro-Ser- Leu-Ser-Ser-Leu-Gly-Glu-Ser-Leu-Glu-Ser-Gly-Ile-Ser-COOH. Several other ELH-related genes are expressed in the atrial gland, an exocrine organ secreting into the oviduct of Aplysia. We review post-translational processing of these ELH-related precursors, and compare the events to those in the neuroendocrine bag cells. Finally, we compare the sequences of six ELH-related peptides from Aplysia with one ELH-related peptide (caudodorsal cell hormone) from Lymnaea to gain insight into the structure-activity relations of ELH at the ovotestis receptor.

The catalytic proficiency and rate enhancement for the hydrolysis of hippurylphenylalanine by carboxypeptidase A under given reaction conditions are calculated from the observed data. Naphthalenedialdehyde, in the presence of cyanide, NDA/CN, is used to measure the uncatalyzed rate of hydrolysis of the peptide bond without the use of high temperature and pH conditions. Various stages of the reaction are monitored by reverse-phase high performance liquid chromatography. The calculations show that the hydrolysis reaction is a first order with respect to peptide.

The immune system cuts foreign invaders into little pieces, which are then displayed on the surface of cells. There, bound to one of two proteins--major histocompatibility complex (MHC) class I [...]

A study of fragmentation of 25 protonated peptide ions in quadrupole ion trap mass spectrometer by matrix-assisted laser desorption/ionization shows that cleavages adjacent to acidic residues are prominent in fragmentation. Observation of preferential fragmentation adjacent to glutamic acid residues shows selective fragementation at Asp and Glu.

A tandem mass spectrometric method that includes electrospray ionization (ESI) and surface-induced dissociation (SID) helps determine fragmentation efficiency curves of peptides. The amino acid sequence of gas-phase protonated peptides influences the efficiency curves. Fragmentation of protonated peptides produced by ESI is more difficult than peptides formed by 6 ke V Cs+ ion bombardment (LSIMS). Fragmentation patterns reveal that ion structures formed by LSIMS are more complex than those produced by ESI.

The goal of quantitative proteomics is to examine the expression levels of all of the proteins in a biological system and recognize those that change as a function of some stimulus. Quantification is now frequently based on derivatization of peptides with isotopically distinguishable labeling agents. This study examines the extent to which isotopic forms of peptides having the same amino acid sequence are resolved by reversed-phase chromatography and assesses the degree to which resolution of these isotopically different forms of a peptide impact quantification. Three derivatizing agents were examined, the [d.sub.0] and [d.sub.3] forms of N-acetoxysuccinimide, the [d.sub.0] and [d.sub.4] forms of succinic anhydride, and the [d.sub.0] and [d.sub.8] forms of the commercial ICAT reagent. Peptide mixtures from control and experimental samples were derivatized individually, mixed, subjected to reversed-phase chromatography, and analyzed by ESI-MS. When partial resolution of the isotopic forms of a peptide occurs, the largest error in assessing the true isotope ratio in a sample occurs when sampling at the extremes of a peak. Early in the elution of a peak, the sample will be enriched in the deuterated species, whereas the opposite is true at the tailing edge of a peak. Acetylated peptides showed the lowest degree of separation. Resolution of the deuterated and nondeuterated forms in this case was 0.023. This amounts to slightly over a 1-s difference in their peak maxima and can cause a typical error of [+ or -]6% at the leading and tailing edges of a peak. In contrast, resolution of the deuterated and nondeuterated forms of the ICAT reagent were calculated to be 0.45. This means that in a peak of l-min width (W1/2), the peak maxima will vary by ~ 30 s, and measurement errors of-83 and +500% can occur at the leading and tailing edges of a peak. It is concluded that resolution of isotopic forms of a peptide can cause substantial quantification errors in quantitative proteomics.

The integration of proline residues with alpha-helical peptides significantly influences the latter's antibacterial and synergistic activities. Through the use of circular dichroism procedures, it was found that increased levels of proline residues tend to decrease the percent helicity of such peptides. Lack of proline residues has also been shown to increase the activity of activity of alpha-helical peptides against gram-negative and gram-positive bacteria.