Synthesis of polyamide supports for use in peptide synthesis and as peptide-resin conjugates for antibody production.

We have synthesized beaded, hydrophilic cross-linked, aminoalkyl polydimethylacrylamide supports upon which peptides have been assembled using standard Boc or Fmoc chemistry in automated equipment. The resins were prepared by the free radical-initiated co-polymerization of N,N-dimethylacrylamide, N,N'-bisacrylyl-1,3-diaminopropane, and a functional monomer which were contained in a reverse-phase, detergent-emulsified suspension. The functional monomers used were N-(2-(methylsulfonyl)ethyloxycarbonyl)-allyl-amine (MSC-allylamine), N-acrylyl-1,6-diaminohexane hydrochloride or N-methacrylyl-1,3-diamino-propane hydrochloride. The MSC protecting group was removed by treatment of the resin with methanolic base during workup. After coupling of N-alpha-t-butyloxycarbonyl-alanine (Boc-alanine), amino acid analyses gave resin loading capacities between 0.15 mmol/g and 1.4 mmol/g, depending on the concentration and composition of the functional monomer. The resulting polymers were highly swollen by polar solvents including aqueous buffers. Peptides were synthesized on these supports after attaching the first amino acid directly or through a cleavable ester linker. When the carboxyl-terminal amino acid was coupled as the 4-oxymethylbenzoic acid derivative, the peptide could be deprotected and remain attached to the hydrophilic polymer since the peptide-benzyl ester bond was stable to HF deprotection at 0 degrees in the presence of 10% anisole and 1% ethanedithiol. The resulting peptidyl-resin could be swollen in aqueous buffers and injected into animals for the production of antibodies.     

Primary sequence mapping of human apolipoprotein B-100 epitopes. Comparisons of trypsin accessibility and immunoreactivity and implication for apoB conformation

Differential trypsin-accessibility and monoclonal antibodies (Mabs) to human apolipoprotein (apo) B-100 are both important tools for probing apoB structure and conformation on low-density lipoproteins (LDL). In this study, we have mapped greater than 80% of the C-terminal region (720 residues) of LDL apoB-100 using trypsin digestion. Our results extend our previous data [Yang et al. (1986) Nature (Lond.) 323, 738-742] confirming that the C-terminal region of about 420 residues of apoB-100 is largely inaccessible to trypsin, whereas the part just preceding this region has interspersed trypsin-accessible and inaccessible peptides. We have determined the amino acid sequence of specific apoB-100 peptides containing epitopes recognized by four separate Mabs: two epitopes have been mapped to within 20 residues, one has been mapped to 36 residues, and the last to 80 residues. We used polyclonal antisera to identify 16 overlapping clones of varying lengths of apoB-100 cDNAs extending from the C-terminus of apoB-100 cloned in the expression vector, lambda gt11. These clones were then tested against individual Mabs. By nucleotide sequence analysis of overlapping clones that show differential reactivities to different Mabs, we have mapped the individual epitopes of each Mab to within about 50-150 amino acid residues predicted from the DNA sequences. Confirmation and further fine mapping were accomplished by competition for LDL binding using partially purified fusion proteins and chemically synthesized oligopeptides. Two epitopes (Mabs 7 and 22) were mapped to the C-terminal 20 amino acids of apoB-100, one (Mab 16) to residues 4154-4189, and another (Mab 20) to residues 3926-4005. Mab 16 precipitates more than 80% of LDL particles. Mab 20 precipitates only denatured apoB but not native LDL apoB [Milne et al. (1987) Mol. Immunol. 24, 435]. Mabs 7 and 22 are unique in that they precipitate LDL apoB modified by storage much better than freshly isolated LDL-apoB. Although epitope expression and trypsin-accessibility represent two useful probes for the study of protein conformation, there was no obvious correlation between these two parameters when applied to LDL apoB for the antibodies we have examined.     

Microbially Mediated Mn(II) Oxidation in an Oligotrophic Arctic Lake

Rates of oxidation of Mn(II) were measured by an in situ incubation technique in the water column of Toolik Lake, Alaska. Measured rates were lower than those observed in other aquatic systems but were sufficient to oxidize all Mn(II) in the lake within a 3-month period. Measured rates compared favorably with rates estimated from a previous study of the geochemical cycling of Mn in Toolik Lake. The Mn(II) oxidation was largely microbially mediated, as indicated by inhibition of oxidation rates by sodium azide. Azide had been previously demonstrated to be a suitable microbial poison for studying Mn(II) oxidation in seawater. This study demonstrates that azide is also a suitable poison for freshwaters and that it inhibits microbial but not abiotic oxidation of Mn(II). Manganese(II) oxidation rates were similar during cold, under-ice conditions in early spring and during warmer summer conditions. This observation suggests that Mn(II) concentration, rather than temperature or oxygen concentration, is the most important factor regulating Mn(II) oxidation rates in Toolik Lake.     

Substitution of Ser61----Gly61 in human apolipoprotein C-II does not alter its activation of lipoprotein lipase

Lipoprotein lipase (LpL) activity is enhanced by apolipoprotein C-II (apoC-II), a 79 amino acid residue peptide. The minimal apoC-II sequence required for activation of LpL resides between residues 56-79. To determine the possible role of an acyl-apoC-II intermediate involving Ser61 in enzyme catalysis, a synthetic peptide of apoC-II containing residues 56-79 was synthesized and compared to the corresponding peptide with serine at position 61 being substituted with glycine. With two different LpL assay systems, both peptides enhanced enzyme activity. Since glycine does not contain a hydroxyl group, these results rule out the possibility that an acyl-apoC-II intermediate with Ser61 is required for enzyme activation.     

Organic free radical levels in seeds and pollen: The effects of hydration and aging

In view of their possible role in oxidative deterioration of seeds and pollen, organic free radicals were measured by electron spin resonance in embryonic axes and cotyledons of soybean [ Glycine max (L.) Merr], embryo and endosperm fractions of corn [ Zea mays L.] and pollen of cattail [ Typha latifolia L.]. A pronounced decline in the radical signal ensued when hydration increased above about 7% (wet weight basis) in both the seed materials and in pollen. Moderate hydration of the soybean axis followed by drying led to a small decrease in organic free radicals compared to untreated material, especially if the desiccation step was performed under nitrogen. In a comparison of soybeans of various ages under normal storage, organic free radical levels in the axis showed little or no increase with age. In marked contrast, over 5 days of accelerated aging at 40°C and near-saturating humidity, organic radical levels approximately doubled in the axis. This pronounced increase in free radical content was not associated with a decrease in the proportion of polyunsaturated fatty acids. The data suggest that hydration of seed and pollen causes a release of free radicals from the trapped state.     

Molecular cloning and sequencing of the gene for CDP-diglyceride synthetase of Escherichia coli

The cds gene of Escherichia coli codes for the enzyme CDP-diglyceride synthetase. We now report the construction of plasmids which carry cds. Using these plasmids, we have sequenced 1274 base pairs of DNA, including a 750-base pair open reading frame which is the coding region of the cds gene. This DNA sequence allows the deduction of the primary peptide sequence for CDP-diglyceride synthetase. The protein is very hydrophobic, and, assuming no processing or modification, has a molecular weight of 27,570. Furthermore, there is a second open reading frame immediately after cds, implying that cds may be part of an operon. We have also constructed a runaway replication cds-plasmid that directs approximately 50-fold overproduction of CDP-diglyceride synthetase. This overproduction has been utilized in the purification of the enzyme to homogeneity, as described in the accompanying paper (Sparrow, C.P., and Raetz, C.R.H., J. Biol. Chem. 260, 12084-12091). Finally, the molecular cloning work reported herein allows the exact placement of the cds gene on the E. coli genetic map.