Solid-phase synthesis of polymyxin B1 and analogues via a safety-catch approach.

As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.     

Localization of cathepsin D in rat liver. Immunocytochemical study using post-embedding immunoenzyme and protein A-gold techniques

Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.     

Catalytic properties of a human cytomegalovirus-induced protein kinase

Human cytomegalovirus, a DNA virus whose genome contains a fragment of transforming DNA, induces a threonine-serine protein kinase having a molecular mass of 68 kDa (p68). p68 was extracted from cells 96-144 h after infection, and immunoprecipitated with a monoclonal antibody (F6b). Antibody-enzyme complexes were immobilized on heat/formaldehyde-inactivated Staphylococcus aureus. The best substrates for p68 were acidic proteins, phosvitin and casein. Glycogen synthase, phosphorylase alpha and histones were phosphorylated at rates not higher than 1-4% that obtained with phosvitin as substrate. ATP and GTP were equally good substrates of p68. p68 is able to autophosphorylate at the same residues (i.e. threonine and serine) as the protein substrates. Autophosphorylation does not seem to represent an intermediate in substrate phosphorylation. The protein kinase activity of p68 was not enhanced by cAMP, calcium ions, or polyamines like spermine or spermidine. Only at low Mg2+ concentration spermine enhanced by 68% the rate of casein phosphorylation. Heparin, a potent inhibitor of casein kinase II, inhibits p68 activity too, but ten-times higher concentrations were required for the same degree of inhibition. Quercetin, a bioflavonoid, acts as a strong inhibitor of p68 protein kinase activity. The inhibitory effect of quercetin was competitive towards the nucleotide substrate (Ki = 2.8 microM), and non-competitive towards the protein substrate (Ki = 15 microM).     

Analysis of three-dimensional ciliary beating by means of high-speed stereomicroscopy.

Results are presented on the analysis of three-dimensional motion of compound cilia or cirri in voltage-clamped specimens of the protozoan Stylonychia mytilus. Time series of three-dimensional data were obtained by using the anaxial illumination method for simultaneous recording of stereoscopic video images. Data processing involved the following steps: determination of a reference coordinate system based solely on features present in each stereo-pair; tracing of cirral axes in digitized images, conversion to parameter curves by means of least-squares polynomial approximation, conversion of pairs of two-dimensional data to a series of three-dimensional data; correction for distortion due to projective shortening and conversion to a series of polynomial triplets, and analysis of the periodical components of the motion pattern in the frequency domain. Reconstructed beating cycles show typical differences between hyperpolarization-induced ciliary activity and depolarization-induced ciliary activity. Reconstructions of the motion of the basal segment of a cirrus are in agreement with existing data. Analysis of the curvature and torsion of a cirral axis during beating does not reveal any simple pattern of propagated activity within the axoneme. The return stroke may be subdivided into two phases. First, a curvature peak develops proximally. Secondly, a region with increased torsion arises more distally and spreads out in proximal direction. Both curvature and torsion return to minimal values by the beginning of the power stroke.     

Conformational differences between linear alpha (2----8)-linked homosialooligosaccharides and the epitope of the group B meningococcal polysaccharide

The alpha-(2----8)-linked sialic acid oligosaccharides (NeuAc)n exhibit an unusual degree of heterogeneity in the conformation of their linkages. This was diagnosed by observation in their 13C NMR spectra of an equivalent and unique heterogeneity in the chemical shifts of their anomeric carbons and subsequently confirmed by more comprehensive 1H and 13C NMR studies. In these studies both one-dimensional and two-dimensional experiments were carried out on the trisaccharide (NeuAc)3 and colominic acid. In addition to the unambiguous assignment of the signals in the spectra, these experiments demonstrated that both linkages of (NeuAc)3 differed in conformation from each other and from the inner linkages of colominic acid. The NMR data indicate that these conformational differences extend to both terminal disaccharides of oligosaccharides larger than (NeuAc)5, a result that has considerable physical and biological significance. In the context of the group B meningococcal polysaccharide, it provides an explanation for the conformational epitope of the group B meningococcal polysaccharide, which was proposed on the evidence that (NeuAc)10, larger than the optimum size of an antibody site, was the smallest oligosaccharide able to bind to group B polysaccharide specific antibodies. Because the two terminal disaccharides of (NeuAc)10 differ in conformation to its inner residues, the immunologically functional part of (NeuAc)10 resides in its inner six residues. This number of residues is now consistent with the maximum size of an antibody site.     

Dissociation of inductive from differentiative signals transmitted by C8-substituted guanine ribonucleosides to B cells from SJL mice

A hitherto unknown defect in the immune responsiveness of B lymphocytes from SJL mice has enabled us to distinguish two qualitatively distinct classes of signal delivered to B cells by C8-substituted guanine ribonucleosides. This defect renders B cells from SJL mice unresponsive to the inductive (early acting) signal of 8-mercaptoguanosine (8MGuo) that culminates in mitogenesis and nonspecific secretion of immunoglobulin. Unresponsiveness is not attributable to a shift in either the dose-response or kinetic profiles, nor can the presence of suppressor cells be demonstrated. In striking contrast, however, SJL B cells exhibit normal responsiveness to the differentiative (T cell-like, or late acting) signal provided by the substituted nucleoside. This signal enables SJL B cells, depleted of T cells, to respond to T cell-dependent antigens, and synergizes with T cell-derived lymphokines. These data suggest 1) that nonspecific secretion of immunoglobulin is dependent on both inductive and differentiative signals, 2) that antigen alone can supply an effective inductive signal for antigen-specific responses, and 3) that the SJL mouse will provide a useful model for selective study of inductive vs differentiative events.