Macromolecular synthesis in organ cultures of neonatal rat lung

Organ cultures of newborn rat lungs synthesize and accumulate DNA, RNA, collagen and noncollagenous proteins almost at a linear rate for at least 5 days. During this period the synthesis of collagen consistently exceeds the synthesis of noncollagenous proteins in a pattern similar to neonatal lung growth in vivo. Although some morphological characteristics of lung architecture are distorted after culture, fundamental structural similarities to lungs growing in intact animals are retained. When these cultures are maintained in atmospheres rich in oxygen, increased collagen synthesis is observed, a response similar to that of lungs in intact animals exposed to high oxygen concentrations in vivo. Our studies suggest that lung organ cultures may be a suitable system for investigating the biochemical aspects of lung tissue-environmental interaction. These studies were supported in parts by NIH Grant HL-19668, a contract (68-03-2005) from the U.S. Environmental Protection Agency, and grants from the California Lung Association.     

On Comparing Correlated Means in the Presence of Incomplete Data

Two statistics are proposed for testing the hypothesis of equality of the means of a bivariate normal distribution with unknown common variance and correlation coefficient when observations are missing on both variates. One of the statistics reduces to the one proposed by Bhoj (1978, 1984) when the unpaired observations on the variates are equal. The distributions of the statistics are approximated by well known distributions under the null hypothesis. The empirical powers of the tests are computed and compared with those of some known statistics. The comparison supports the use of one of the statistics proposed in this paper.     

Inactivation of yeast hexokinase by o-phthalaldehyde: evidence for the presence of a cysteine and a lysine at or near the active site

Yeast hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), a homodimer, was rapidly and irreversibly inactivated by o-phthalaldehyde at 25 degrees C (pH 7.3). The reaction followed pseudo-first-order kinetics over a wide range of the inhibitor concentration. The second-order-rate constant for the inactivation of hexokinase was estimated to be 45 M-1.s-1. Hexokinase was protected more by sugar substrates than by nucleoside triphosphates during inactivation by o-phthalaldehyde. Absorption spectrum (lambda max 338 nm), and fluorescence excitation (lambda max 363 nm) and emission (lambda max 403 nm) spectra of the hexokinase-o-phthalaldehyde adduct were consistent with the formation of an isoindole derivative. These results also suggest that sulfhydryl and epsilon-amino functions of the cysteine and lysine residues, respectively, participating in the isoindole formation are about 3 A apart in the native enzyme. About 2 mol of the isoindole per mol of hexokinase dimer were formed following complete loss of the phosphotransferase activity. Chemical modification of hexokinase by iodoacetamide in the presence of mannose resulted in the modification of six sulfhydryl groups per mol of hexokinase with retention of the phosphotransferase activity. Subsequent reaction of the iodoacetamide modified hexokinase with o-phthalaldehyde resulted in complete loss of the phosphotransferase activity with concomitant modification of the remaining two sulfhydryl groups of hexokinase. Chemical modification of hexokinase by iodoacetamide in the absence of mannose resulted in complete inactivation of the enzyme. The iodoacetamide inactivated hexokinase failed to react with o-phthalaldehyde as evidenced by the absence of a fluorescence emission maximum characteristic of the isoindole derivative. The holoenzyme failed to react with [5'-(p-fluorosulfonyl)benzoyl]adenosine. The dissociated hexokinase could be inactivated by [5'-(p-fluorosulfonyl)benzoyl]adenosine; the degree of inactivation paralleled the extent of reaction between o-phthalaldehyde and the nucleotide-analog modified enzyme. Thus, it is concluded that two cysteines and lysines at or near the active site of the hexokinase were involved in reaction with o-phthalaldehyde following complete loss of the phosphotransferase activity. An important finding of this investigation is that the lysines, involved in isoindole formation, located at or near the active site are probably buried.(ABSTRACT TRUNCATED AT 400 WORDS)     

Interaction of guanosine cyclic 3',5'-phosphate dependent protein kinase with lin-benzoadenine nucleotides

Using the activated cGMP-dependent protein kinase in the presence of the phosphorylatable peptide [[Ala34]histone H2B-(29-35)], we found that lin-benzoadenosine 5'-diphosphate (lin-benzo-ADP) was a competitive inhibitor of the enzyme with respect to ATP with a Ki (22 microM) similar to the Kd (20 microM) determined by fluorescence polarization titrations. The Kd for lin-benzo-ADP determined in the absence of the phosphorylatable peptide, however, was only 12 microM. ADP bound with lower affinity (Ki = 169 microM; Kd = 114 microM). With [Ala34]histone H2B-(29-35) as phosphoryl acceptor, the Km for lin-benzo-ATP was 29 microM, and that for ATP was 32 microM. The Vmax with lin-benzo-ATP, however, was only 0.06% of that with ATP as substrate [0.00623 +/- 0.00035 vs. 11.1 +/- 0.17 mumol (min.mg)-1]. Binding of lin-benzo-ADP to the kinase was dependent upon a divalent cation. Fluorescence polarization revealed that Mg2+, Mn2+, Co2+, Ni2+, Ca2+, Sr2+, and Ba2+ supported nucleotide binding to the enzyme; Ca2+, Sr2+, and Ba2+, however, did not support any measurable phosphotransferase activity. The rank order of metal ion effectiveness in mediating phosphotransferase activity was Mg2+ greater than Ni2+ greater than Co2+ greater than Mn2+. Although these results were similar to those observed with the cAMP-dependent protein kinase [Hartl, F. T., Roskoski, R., Jr., Rosendahl, M. S., & Leonard, N. J. (1983) Biochemistry 22, 2347], major differences in the Vmax with lin-benzo-ATP as substrate and the effect of peptide substrates on nucleotide (both lin-benzo-ADP and ADP) binding were observed.     

Kinetics of reabsorption of nutrients in renal brush border membrane vesicles from rats with experimental ascending pyelonephritis

The uptake of nutrients was investigated in the renal cortical brush border membrane (BBM) vesicles at different stages of ascending pyelonephritis. There was significant difference (p less than 0.05) in the uptake of D-glucose, L-alanine, L-aspartate, L-lysine and L-proline 3 days postinfection and onwards in both right unobstructed and left obstructed experimental kidneys as compared to the sham operated control. The uptake of D-glucose, L-lysine and L-proline was found to be significantly decreased (p less than 0.05) during the course of infection. While uptake of L-alanine and L-aspartate increased (p less than 0.05) in early stages and decreased (p less than 0.05) in later stages of infection. The differential effect was attributed to the compensatory measure and different kinds of transport systems for different types of amino acids.     

Germ cell nucleosomes contain remodeled core protein complex

Electrophoretic analysis of the nucleosomal histones from MN1 and MN2 subpopulations of the seminiferous tubules in gels containing either 6.25 or 2.5 M urea revealed the presence of testis specific histone H2S, H1 and protein ‘A’ in addition to the somatic histones in the core protein complex. Size analysis indicated the presence of a 150–160 bp DNA segment in the MNI subpopulation, whereas, an approx 180 bp DNA fragment was present in the MN2 subpopulation of both liver and tubule nucleosomes. These data suggest an extensive remodeling of the nucleosomal core protein complex during mammalian spermatogenesis.     

Internalization and processing of Bacillus anthracis lethal toxin by toxin-sensitive and -resistant cells

Anthrax lethal toxin consists of two separate proteins, protective antigen and lethal factor (LF). Certain macrophages and a mouse macrophage-like cell line, J774A.1, are lysed by low concentrations of lethal toxin. In contrast, another macrophage cell line, IC-21, and all other cell types tested were resistant to this toxin. To discover the basis for this difference, each step in the intoxication process was examined. No differences between sensitive and resistant cells were found in receptor binding or proteolytic activation of protective antigen, steps that are required prior to LF binding. To determine whether resistance results from a defect in translocation to the cytosol, we introduced LF into J774A.1 and IC-21 cells and a nonmacrophage cell line (L6 myoblast) by osmotic lysis of pinocytic vesicles. Only J774A.1 cells were lysed; no effect was observed in IC-21 and L6 cells. These results suggest that resistant cells either lack the intracellular target of LF or fail to process LF to an active form. The relatively low potency of LF introduced into J774A.1 cells by osmotic lysis suggests that protective antigen may also be required at a stage subsequent to endocytosis.     

A comparison of methods measuring aromatase activity in human placenta and rat ovary

The single step chromatographic product isolation method using [4-14C]-androstenedione and the tritiated water method using either [1 beta, 2 beta-3H]- or [1 beta-3H]-androstenedione have been used to determine a suitable method to measure the aromatase activity in rat ovarian 1000 g supernatant and human placental microsomes. The single step product isolation method using [4-14C]A4 reveals the presence of four distinct [4-14C]-labelled products in the rat ovary of which only the synthesis of estradiol is markedly inhibited by CGS 16949A, a well established aromatase inhibitor. In the human placenta, the formation of both [4-14C]-estrone and [4-14C]-estradiol is strongly inhibited by CGS 6949A. Therefore, in the rat ovary spurious results are obtained if accumulative radiolabelled product formation is measured without characterisation of the products. The Vmax in the rat ovary using [1 beta, 2 beta-3H]-A4 as a substrate is 13.7 pmol/h/mg compared to 2.9 pmol/h/mg when [1 beta-3H]-A4 is used. In the human placenta, the Vmax is similar using either [1 beta, 2 betat-3H]-A4 or [1 beta-3H]-A4 (1.21 and 1.27 nmol/h/mg, respectively). Consistent results are obtained for the human placenta using either the single step chromatographic product isolation method or the tritiated water method. However, in the rat ovary the more suitable method of the two used to measure the aromatase activity is the tritiated water method employing [1 beta-3H]-A4 as a substrate. Aromatase activity in the rat ovary during estrus cycle was measured using the tritiated water method employing [1 beta-3H]-A4 as a substrate. A peak of aromatase activity at proestrus was seen which returned rapidly to its basal level at estrus. Plasma estradiol concentrations were in parallel with the aromatase activity.     

Modeling of nitrogen transformations and translocations

Different submodels within complex model packages on N regimes-for plant N-uptake, net N-mineralization, nitrate leaching and microbial N immobilization-are critically reviewed mainly with regard to their prediction ability on the basis of three comparative papers. Only for some of the processes adequate statistical evaluation of the models was possible. Compared to the other statistically evaluable process, nitrate leaching, modeling of plant N-uptake yields the better results. Most models for mineralization use arbitrary approaches rather than empirical ones. Although only approximate estimates of N mineralisation were at hand, the models generally behave expectedly poor. Only one model-DAISY-out of 16 involved in the comparison uses an explicit microbial biomass sub-model including microbial growth, decline and maintenance terms. So DAISY is the only model coupling C and N cycles. But what is true for an individual model describing the C and N transformation of a lab incubation experiment seems to be valid for most of the complex simulation work on the C and N regimes: this model was said to be overparameterized with respect to the available data.     

TheAspergillus parasiticus polyketide synthase genepksA,a homolog ofAspergillus nidulans wA,is required for aflatoxin B1 biosynthesis

Aflatoxins comprise a group of polyketide-derived carcinogenic mycotoxins produced byAspergillus parasiticus andAspergillus flavus. By transformation with a disruption construct, pXX, we disrupted the aflatoxin pathway inA. parasiticus SRRC 2043, resulting in the inability of this strain to produce aflatoxin intermediates as well as a major yellow pigment in the transformants. The disruption was attributed to a single-crossover, homologous integration event between pXX and the recipientA. parasiticus genome at a specific locus, designatedpksA. Sequence analysis suggest thatpksA is a homolog of theAspergillus nidulans wA gene, a polyketide synthase gene involved in conidial wall pigment biosynthesis. The conservedβ-ketoacyl synthase, acyltransferase and acyl carrier-protein domains were present in the deduced amino acid sequence of thepksA product. Noβ-ketoacyl reductase and enoyl reductase domains were found, suggesting thatpksA does not encode catalytic activities for processingβ-carbon similar to those required for long chain fatty acid synthesis. ThepksA gene is located in the aflatoxin pathway gene cluster and is linked to thenor-1 gene, an aflatoxin pathway gene required for converting norsolorinic acid to averantin. These two genes are divergently transcribed from a 1.5 kb intergenic region. We propose thatpksA is a polyketide synthase gene required for the early steps of aflatoxin biosynthesis.