The leader peptides from bacteriorhodopsin and halorhodopsin are potential membrane-spanning amphipathic helices

We show that the N-terminal leader peptides from the bacterial membrane proteins bacteriorhodopsin and halorhodopsin can be expected to form amphipathic alpha-helics with a highly hydrophobic nonpolar face and a narrow, negatively charged polar face. This finding is discussed in terms of a model for the integration of these proteins into the bacterial membrane.     

Characterization of a heterogeneous camel milk whey non-casein protein

A milk protein, occurring in the whey fraction, has been characterized from camel milk. Determination of the primary structure reveals the existence of two related types of chain with residue differences in at least the N-terminal region. A fragment representing an N-terminal part of the protein was also recovered (heterogeneous at the same positions). The absence of cysteine residues in the protein shows that no disulphide bridges are present. The pattern of fragments and a parent protein resembles that for casein and its fragments, showing that fragments and a multiplicity of forms may be typical for different milk proteins.     

Synthesis and processing of alpha-galactosidase A in human fibroblasts. Evidence for different mutations in Fabry disease

The synthesis and processing of the human lysosomal enzyme alpha-galactosidase A was examined in normal and Fabry fibroblasts. In normal cells, alpha-galactosidase A was synthesized as an Mr = 50,500 precursor, which contained phosphate groups in oligosaccharide chains cleavable by endoglucosaminidase H. The precursor was processed via ill-defined intermediates to a mature Mr 46,000 form. Processing was complete within 3-7 days after synthesis. In the presence of NH4Cl and in I-cell fibroblasts, the majority of newly synthesized alpha-galactosidase A was secreted as an Mr = 52,000 form. For comparison, the processing and stability of alpha-galactosidase A were examined in fibroblasts from five unrelated patients with Fabry disease, which is caused by deficient alpha-galactosidase A activity. In one cell line, synthesis of immunologically cross-reacting polypeptides was not detectable. In another, the synthesis, processing, and stability of alpha-galactosidase A was indistinguishable from that in normal fibroblasts. In a third Fabry cell line, the mutation retarded the maturation of alpha-galactosidase A. Finally, in two cell lines, alpha-galactosidase A polypeptides were synthesized that were rapidly degraded following delivery to lysosomes. These results clearly indicate that Fabry disease comprises a heterogeneous group of mutations affecting synthesis, processing, and stability of alpha-galactosidase A.     

Lysosomal enzyme precursors in coated vesicles derived from the exocytic and endocytic pathways

The molecular forms of two lysosomal enzymes, cathepsin C and cathepsin D, have been examined in lysosomes and coated vesicles (CVs) of rat liver. In addition, the relative proportion of these lysosomal enzymes residing in functionally distinct CV subpopulations was quantitated. CVs contained newly synthesized precursor forms of the enzymes in contrast to lysosomes where only the mature forms were detected. Exocytic and endocytic CV subpopulations were prepared by two completely different protocols. One procedure, a density shift method, uses cholinesterase to alter the density of CVs derived from exocytic or endocytic pathways. The other relies on electrophoretic heterogeneity to accomplish the CV subfractionation. Subpopulations of CVs prepared by either procedure showed similar results, when examined for their relative proportion of cathepsin C and cathepsin D precursors. Within the starting CV preparation, exocytic CVs contained approximately 80-90% of the total steady-state levels of these enzymes while the level in the endocytic population was approximately 10-13%. The implications of these findings are discussed with regard to lysosome trafficking.     

The onset of the respiratory burst in human neutrophils. Real-time studies of H2O2 formation reveal a rapid agonist-induced transduction process

A real-time study of the initiation of the respiratory burst in human neutrophils was made. The cells were stimulated with fMet-Leu-Phe (fMLP) C5a, platelet-activating factor, leukotriene B4, phorbol myristate acetate (PMA), or ionomycin, and H2O2 production was determined by chemiluminescence. Identical average onset times (2.4 s) and closely comparable values for the apparent first-order rate constant (kapp) for the induction of NADPH-oxidase activity (0.21-0.29 s-1) were obtained following stimulation with fMLP, C5a, platelet-activating factor, or leukotriene B4, suggesting that different agonists act through a common transduction sequence. Much longer onset times and lower kapp values were obtained upon stimulation with PMA or ionomycin. Pretreatment with PMA consistently shortened the onset time of the neutrophil's responses to agonists by about 1 s. When H2O2 production was initiated with PMA, a subsequent stimulation with the agonist fMLP elicited an immediate response (onset time less than 0.2 s) which preceded further changes in fura-2-detected [Ca2+]i. The results are consistent with a mechanism in which agonist signals appear to be transduced by two sequences acting in concert--a rate-limiting one liberating Ca2+ and diacylglycerol and turning on the Ca2+/phospholipid-dependent enzyme protein kinase C, and an essentially instantaneous one which does not appear to require further changes in cytosolic Ca2+.     

Selection of DNA binding sites by regulatory proteins. Statistical-mechanical theory and application to operators and promoters

We present a statistical-mechanical selection theory for the sequence analysis of a set of specific DNA regulatory sites that makes it possible to predict the relationship between individual base-pair choices in the site and specific activity (affinity). The theory is based on the assumption that specific DNA sequences have been selected to conform to some requirement for protein binding (or activity), and that all sequences that can fulfil this requirement are equally likely to occur. In most cases, the number of specific DNA sequences that are known for a certain DNA-binding protein is very small, and we discuss in detail the small-sample uncertainties that this leads to. When applied to the binding sites for cro repressor in phage lambda, the theory can predict, from the sequence statistics alone, their rank order binding affinities in reasonable agreement with measured values. However, the statistical uncertainty generated by such a small sample (only 6 sites known) limits the result to order-of-magnitude comparisons. When applied to the much larger sample of Escherichia coli promoter sequences, the theory predicts the correlation between in vitro activity (k2KB values) and homology score (closeness to the consensus sequence) observed by Mulligan et al. (1984). The analysis of base-pair frequencies in the promoter sample is consistent with the assumption that base-pairs at different positions in the sites contribute independently to the specific activity, except in a few marginal cases that are discussed. When the promoter sites are ordered according to predicted activities, they seem to conform to the Gaussian distribution that results from a requirement for maximal sequence variability within the constraint of providing a certain average activity. The theory allows us to compare the number of specific sites with a certain activity to the number that would be expected from random occurrence in the genome. While strong promoters are "overspecified", in the sense that their probability of random occurrence is very low, random sequences with weak promoter-like properties are expected to occur in very large numbers. This leads to the conclusion that functional specificity is based on other properties in addition to primary sequence recognition; some possibilities are discussed. Finally, we show that the sequence information, as defined by Schneider et al. (1986), can be used directly (at least in the case of equilibrium binding sites) to estimate the number of protein molecules that are specifically bound at random "pseudosites" in the genome.(ABSTRACT TRUNCATED AT 400 WORDS)     

Genetic identification of rat liver carboxylesterases isolated in different laboratories

Six carboxylesterases previously isolated from rat liver microsomes, characterized in Brussels and in Kiel, were compared with genetically defined liver esterases of various reference strains using polyacrylamide gel electrophoresis and isoelectric focusing. The six liver carboxylesterases were identified as alloenzymic forms of ES-3, ES-4, ES-8/ES-10 and ES-15 according to the genetic nomenclature recommended by van Zutphen (Van Zutphen, L.F.M. (1983) Transplant. Proceed. 15, 1687-1688). The genetic and biochemical characteristics of the four isoenzymes are summarized, and their identity with several other drug-metabolizing esterases/amidases and lipases of rat liver endoplasmic reticulum is discussed.     

Genome relationship betweenPsathyrostachys huashanica andP. fragilis (Poaceae)

Hybrids between the Chinese endemic speciesPsathyrostachys huashanica Keng and the SW. Asian speciesP. fragilis (Boiss.)Nevski (all 2n = 14) developed normally but were completely sterile. Meiotic analyses revealed a high chiasma frequency indicating that the two species as well asP. juncea (Fisch.)Nevski share the same basic genome (called N). The hybrid nature of the plants was established through karyotype analysis and Giemsa C-banding.     

Kinetics of carbonyl reductase from human brain.

Initial-rate analysis of the carbonyl reductase-catalysed reduction of menadione by NADPH gave families of straight lines in double-reciprocal plots consistent with a sequential mechanism being obeyed. The fluorescence of NADPH was increased up to 7-fold with a concomitant shift of the emission maximum towards lower wavelength in the presence of carbonyl reductase, and both NADPH and NADP+ caused quenching of the enzyme fluorescence, indicating formation of a binary enzyme-coenzyme complex. Deuterium isotope effects on the apparent V/Km values decreased with increasing concentrations of menadione but were independent of the NADPH concentration. The results, together with data from product inhibition studies, are consistent with carbonyl reductase obeying a compulsory-order mechanism, NADPH binding first and NADP+ leaving last. No significant differences in the kinetic properties of three molecular forms of carbonyl reductase were detectable.