No abstract

The relative molar sensitivities for a number of compounds having a variety of functional groups were obtained in gas chromatography electron ionization mass spectrometry. Comparable results were obtained with a quadrupole and with a magnetic mass spectrometer. The present relative molar sensitivities are in good agreement with relative ionization cross sections obtained by different techniques and different instruments for a variety of compounds with molecular weights below about 200 u. For compounds of higher molecular weight, the present experimental sensitivities are significantly larger than estimates extrapolated from earlier data. The relatively molar sensitivities correlate well with molecular polarizability.

A number of phosphatidylcholines have been isolated from an HIV-1/MN preparation by reversed-phase high-performance liquid chromatography (HPLC) and analyzed by fast atom bombardment mass spectrometry (FABMS), FABMS/MS, and FABMS/MS/MS in both positive- and negative-ion modes. Negative-ion FABMS/MS with high-energy collisions was used to identify the length of the acyl groups and the degree of saturation, as well as their position on the glyceride group. FABMS/MS in the positive-ion mode was used to identify the polar head group. Negative-ion FABMS/MS/MS was used to locate positions of double bonds in acyl groups. We find that four-sector tandem mass spectrometry with high-energy collisional activation provides qualitative analysis of viral phosphatidyl lipids in considerable detail, as well as semiquantitative information. Approximate quantitation of the phosphatidylcholine content of the HIV-1/MN preparation by measuring relative peak heights of molecular ions in FABMS reveals an array of phosphatidylcholines consistent with that found in human erythrocytes, indicating the likely source of lipids in the viral membrane to be the host cell membrane.

During oviposition, female Sirex noctilio (F.) (Siricidae) woodwasps inject their conifer hosts with a venom gland secretion. The secretion induces a variety of host physiological changes that facilitate subsequent lethal infection by a symbiotic fungus. A heat-stable factor that can migrate from the site of oviposition in the trunk through the xylem to needles in the crown of attacked pines was purified by size-fractionation and reversed-phase–high-performance liquid chromatography using activity assays based on defense gene induction as well as the needle wilt response in pine shoot explants. An 11-amino acid, posttranslationally modified peptide (SEGPROGTKRP) encoded by the most abundant transcript recovered from S. noctilio venom gland tissue comprised the backbone of the 1,850 Da active factor. Posttranslational modifications included hydroxylation of a Pro residue at position 6 as well as O-glycosylation of Ser and Thr residues at positions 1 and 8, respectively. The O-linked sugars were identical α-linked N-acetylgalactosamine residues modified at the C6 position by addition of phosphoethanolamine. In contrast to the native peptide, a synthetic version of the hydroxylated peptide backbone lacking the glycosyl side chains failed to induce pine defense genes or cause needle wilt in excised shoots. This peptide, hereafter called noctilisin, is related to the O-glycosylated short-chain proline-rich antimicrobial peptides exemplified by drosocin. The noctilisin structure contains motifs which may explain how it avoids detection by pine defense systems.