Preparation of O-phosphotyrosine-containing peptides by Fmoc solid-phase synthesis: Evaluation of several Fmoc-Tyr(PO3R2)-OH derivatives

Summary The synthesis of two model Tyr(P)-containing peptides using Fmoc-Tyr(PO₃ tBu₂)-OH, Fmoc-Tyr(PO₃Bzl₂)-OH and Fmoc-Tyr(PO₃H₂)-OH established that the t-butylphosphate-protected derivative was the preferred derivative for use in Fmoc solid-phase peptide synthesis, since it afforded phosphopeptides in high purity and with the lowest amount of Tyr-peptide contamination. In addition, this study confirmed that commercially available Fmoc-Tyr(PO₃H₂)-OH is also suitable for use in Fmoc solid-phase synthesis but gives less pure phosphopeptides, along with the generation of 1–4% of the tyrosine-containing peptide for the model sequences studied. In view of the good performance of Fmoc-Tyr(PO₃ tBu₂)-OH, a large-scale three-step synthetic procedure was developed which involved phenacyl protection of the carboxyl group, phosphite-triester phosphorylation of the tyrosyl hydroxyl using di-t-butyl N,N-diethylphosphoramidite, and final removal of the phenacyl group by zinc reduction in acetic acid.Abbreviations BOP benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate - tBu t-butyl - Bzl benzyl - DBU 1,8-diazabicyclo[5,4,0]undec-7-ene - DMF N,N-dimethylformamide - EDT ethanedithiol - Fmoc 9-fluorenylmethoxycarbonyl - HOBt N-hydroxybenzotriazole - HPLC high performance liquid chromatography - NMM N-methylmorpholine - Pac phenacyl - TFA trifluoroacetic acid - THF tetrahydrofuran - Tyr(P) O-phosphotyrosine     

Synthesis and evaluation of azaproline peptides as potential inhibitors of dipeptidyl peptidase IV and prolyl oligopeptidase

Summary A series of azaproline dipeptides with various N-substituents were synthesized as possible active-site-directed inhibitors of two proline-specific serine proteases, dipeptidyl peptidase IV and prolyl oligopeptidase. Compounds with semicarbazide, carbazate, acylhydrazine and sulphonylhydrazine structures were tested. Some compounds show moderate activity, i.e., in the millimolar range.     

Brain CCK receptors are structurally distinct from pancreas CCK receptors

Brain and pancreas cholecystokinin (CCK) receptors differ markedly in their selectivity for CCK analogs. To determine the size and subunit structure of the brain CCK receptor and compare it to that of the pancreas, 125I-CCK33 was covalently cross-linked with ultraviolet light to its receptor on mouse brain particles and purified pancreatic plasma membranes. When CCK was crosslinked to brain membranes, a single consistent major labeled protein band of Mr = 55,000 was observed in both the presence and the absence of DTT. These data with brain receptors contrast to results with pancreatic receptors where two bands of Mr = 120,000 and 80,000 are labeled in the absence and presence of DTT, respectively. These studies indicate, therefore, that the brain and pancreas CCK receptors are structurally and functionally distinct.     

Binding of simple carbohydrates and some N-acetyllactosamine-containing oligosaccharides to Erythrina cristagalli agglutinin as followed with a fluorescent indicator ligand

Erythrina cristagalli agglutinin, a dimeric lectin [J. L. Iglesias, et al. (1982) Eur. J. Biochem.123, 247–252] was shown by equilibrium dialysis to be bivalent for 4-methylumbelliferyl-β-d-galactoside. Upon binding to the lectin, this ligand showed a difference absorption spectrum with two maxima (at 322 and 336 nm) of equal intensity (Δ? = 1.2 × 10³m^?1 cm^?1). A similar spectrum with a comparable value of Δ? was obtained with 4-methylumbelliferyl-N-acetyl-β-d-galactosaminide. Binding of methyl-α-d-galactoside, lactose, and N-acetyllactosamine all produced small but equally intense protein difference spectra with a maximum (Δ? = 2.8 × 10² M^?1 cm^?1) at 291.6 nm. Upon binding of N-dansyl-d-galactosamine to the lectin, there was a fivefold increase in fluorescence intensity of this ligand. The association constant for N-dansyl-d-galactosamine was caused by a very favorable ΔS° of the dansyl group without affecting the strictly carbohydrate-specific character of binding. N-Dansyl-d-galactosamine was employed as a fluorescent indicator ligand in substitution titrations. This involved the use of simple carbohydrates, N-acetyllactosamine, and oligosaccharides which occur in the carbohydrate units of N-glycoproteins; the latter were Gal(β → 4)GlcNAc(β1 → 2)Man, Gal(β1 → 4)GlcNAc(β1 → 6)Man, and Gal(β1 → 4)GlcNAc(β1 → 6)[Gal(β1 → 4)GlcNAc(β1 → 2)]Man. The titrations were performed at two temperatures to determine the thermodynamic parameters. In the series N-acetyl-d-galactosamine, methyl-α-d-galactoside, and lactose, ?ΔH° increased from 24 to 41 kJ mol^?1; it increased further for N-acetyllactosamine and then remained unchanged for the N-acetyllactosamine-containing oligosaccharides (55 ± 1 kJ mol^?1). This indicated that the site specifically accommodated the disaccharide structure with an important contribution of the 2-acetamido group in the penultimate sugar. Beyond this, no additional contacts seemed to be formed. This conclusion also followed from considerations of ΔS° values which became more unfavorable in the above series (?23 to ?101 ± 4 J mol^?1 K^?1); the most negative value of ΔS° was observed with N-acetyllactosamine and the three N-acetyllactosamine-containing oligosaccharides.     

Occurrence of multiple forms of alcohol dehydrogenase in Penicillium supplemented with 2,3-butanediol

The NAD-dependent oxidation of ethanol, 2,3-butanediol, and other primary and secondary alcohols, catalyzed by alcohol dehydrogenases derived from Penicillium charlesii, was investigated. Alcohol dehydrogenase, ADH-I, was purified to homogeneity in a yield of 54%. The enzyme utilizes several primary alcohols as substrates, with K_m values of the order of 10^?4m. A K_m value of 60 mm was obtained for R,R,-2,3-butanediol. The stereospecificity of the oxidation of 2-butanol was investigated, and S-(+)-2-butanol was found to be oxidized 2.4 times faster than was R-(?)-2-butanol. The reduction of 2-butanone was shown to produce S-(+)-2-butanol and R-(?)-butanol in a ratio of 7:3. ADH-I is the primary isozyme of alcohol dehydrogenase present in cultures utilizing glucose as the sole carbon source. The level of alcohol dehydrogenase activity increased 7.6-fold in mycelia from cultures grown with glucose and 2,3-butanediol (0.5%) as carbon sources compared with the activity in cultures grown on only glucose. Two additional forms of alcohol dehydrogenase, ADH-II and ADH-III, were present in the cultures supplemented with 2,3-butanediol. These forms of alcohol dehydrogenase catalyze the oxidation of ethanol and 2,3-butanediol. These data suggest that P. charlesii carries out an oxidation of 2,3-butanediol which may constitute the first reaction in the degradation of 2,3-butanediol as well as the last reaction in the mixed-acid fermentation. Alcohol dehydrogenase activities in P. charlesii may be encoded by multiple genes, one which is expressed constitutively and others whose expression is inducible by 2,3-butanediol.     

Junction formation in aggregated embryonal carcinoma cells

Under the action of supplemental calcium, H6 mouse embryonal carcinoma cell aggregates undergo compaction, a morphological phenomenon similar to mouse embryonic compaction. Formation of various types of cell junctions, especially gap junctions, is associated with compaction of the embryo and we sought to analyze the pattern of junction formation during aggregation and compaction of H6 cells. At 24 hr of aggregation, gap junctions were abundant in both uncompacted and compacted aggregates but quantitative analysis of freeze fracture replicas of these junctions showed a 20-fold increase in the size of the largest gap junctions in compacted aggregates. Such a difference in size could even be detected at 12 hr of aggregation. Tight junctions were not normally formed in 12 hr aggregates but initial stages of tight junction formation could be noticed in 12 hr compacted aggregates. More definitive tight junctions and desmosomes were evident only after 48 hr of aggregation. Thus we have observed that both uncompacted and compacted aggregates can form gap junctions at similar frequencies, suggesting that cell flattening, which contributes to the compacted morphology, is not a requisite for gap junctions. Likewise, generation of the compacted morphology seems to be independent of gap junction formation. This supports the idea that compaction in embryonal carcinoma cells results from calcium-induced cell flattening, probably through the mobilization of cytoskeletal elements. Calcium-dependent features of H6 cell aggregation and compaction enables the independent analysis of separate steps in compaction.     

Stage-specific expression of three cell surface carbohydrate antigens during murine spermatogenesis detected with monoclonal antibodies

We have identified three germ cell surface carbohydrate antigens that exhibit a common, stage-specific pattern of expression during spermatogenesis in the mouse. IgM-class monoclonal antibodies designated "J1," "C6," and "A5" were absorbed by adult testis, but not by any adult somatic tissue tested. In indirect immunofluorescence assays using collagenase-dissociated prepuberal and adult testicular cells, these antibodies labeled the surfaces of early and late pachytene spermatocytes and round spermatids. Gonocytes from fetal and neonatal testes were not labeled. In paraffin sections of prepuberal and adult testes, sialidase treatment exposed antigens recognized by antibodies C6 and A5 on preleptotene, leptotene, and zygotene spermatocytes located near the perimeter of seminiferous tubules. The determinants recognized by antibodies J1, C6, and A5 were characterized partially using a sugar hapten inhibition assay. The binding of J1 to adult testicular cells was inhibited specifically by N-acetylglucosamine and the binding of both C6 and A5 was inhibited by N-acetyllactosamine. The glycoconjugates recognized by J1, C6, and A5 eluted from gel filtration columns with an apparent molecular weight greater than 1 X 10(6) and were sensitive to endo-beta-galactosidase (keratanase) treatment. The apparent high molecular weight of these glycoconjugates was confirmed by immunolabeling Western blots of testis extracts separated by SDS-polyacrylamide gel electrophoresis. The results suggest that polylactosamine (keratan) glycoconjugates of high molecular weight are associated with the plasma membranes of meiotic and haploid male germ cells. The effects of sialidase on antibody labeling patterns suggest that changes in cell surface sialylation accompany the transition of early meiotic germ cells to pachytene spermatocytes during spermatogenesis.     

Optimizing conditions for cryopreservation of an insect cell line

A cell line (UM-BGE-2) derived from embryos of the cockroach Blattella germanica was frozen to ?196 °C under a variety of conditions and cell viability was assayed after warming. It was found that cell viability was affected by the cooling rate, the warming rate, the controlled cooling endpoint temperature, and the type and concentration of cryoprotectant. The best survival for cells suspended in Grace's tissue culture medium containing 1 M Me₂SO was obtained when cells were cooled at 1 °C/ min to at least ?90 °C before being placed in liquid nitrogen and warmed at more than 900 °C/min. Cultures initiated from these frozen cells produce typical growth curves and appear normal after several passages.     

1H NMR of glycosaminoglycans and hyaluronic acid oligosaccharides in aqueous solution: the amide proton environment

The exchangeable amide protons of hyaluronic acid (HA) oligosaccharides and a higher-molecular-weight segment dissolved in H2O at pH 2.5 or 5.5 were examined by H NMR spectroscopy at 250 MHz. The HA segment preparation showed a single amide resonance, near the chemical shift for the amide proton of the monosaccharide 2-acetamido-2-deoxy-beta-D-glucopyranose (beta-GlcNAc). Smaller HA oligosaccharides showed two or three separate amide proton resonances, corresponding in relative peak area to interior or end GlcNAc residues. The interior GlcNAc amide resonance occurred at the same chemical shift as the single resonance of the HA segment. For the end GlcNAc residues, linkage to D-glucuronopyranose (GlcUA) through C1 resulted in an upfield shift relative to the beta-anomer of GlcNAc, whereas linkage through C3 resulted in a downfield shift relative to the corresponding anomer of GlcNAc. These chemical-shift perturbations appeared to be approximately offsetting in the case of linkage at both positions. The amide proton vicinal coupling constant (ca. 9 Hz) was found to be essentially independent of chain length, residue position, or solution pH. These data favor a nearly perpendicular orientation for the acetamido group with respect to the sugar ring, little affected by linkage of GlcNAc to GlcUA. No evidence for the existence of a stable hydrogen bond linking the amide proton with the carboxyl(ate) oxygen of the adjacent uronic acid residue was found. The amide proton resonances for chondroitin, chondroitin 4-sulfate, and dermatan sulfate were compared to that of HA. The chemical shifts of these resonances deviated no more than 0.1 ppm from that of HA. A small dependence on the identity of the adjacent uronic acid residue was noted, based on the observation of two resonances for dermatan sulfate.     

A diphenylmethane derivative specific for the antiestrogen binding site found in rat liver microsomes

A new para-diphenylmethyl derivative, N,N-diethyl-2-[(4-phenylmethyl)-phenoxy]-ethanamine·HCl (N,N-DPPE) has been synthesized which binds with high affinity to the anti-estrogen binding site found in male rat liver microsomes. However, no evidence of significant interaction with the estrogen receptor can be observed at or below 10 μM in rat uterine cytosols; 10 nM N,N-DPPE fails to significantly induce progesterone receptor in MCF-7 cells. Tamoxifen also binds to anti-estrogen binding site but, unlike N,N-DPPE, binds significantly to estrogen receptor at much loeer concentrations and induces MCF-7 progesterone receptor. This property of high affinity for anti-estrogen binding site but not for estrogen receptor may make N,N-DPPE an important probe for the study of anti-estrogen binding site and its biological relevance.