Structure of apolipoprotein B-100 of human low density lipoproteins

We have analyzed low density lipoproteins (LDL) apolipoprotein (apop) B structure by direct sequence analysis of LDL apo B-100 tryptic peptides. Native LDL were digested with trypsin, and the products were fractionated on a Sephadex G-50 column. The partially digested apo B-100 still associated with lipids was recovered in the void volume (designated trypsin-nonreleasable, TN, peptides). The released peptides (designated trypsin-releasable, TR, peptides) in subsequent peaks were repurified on two successive high-performance liquid chromatography (HPLC) columns. The TN peak was delipidated and redigested with trypsin, and the resulting peptides were purified on two successive HPLC columns. Using this approach, we sequenced over 88% of LDL apo B-100, extending and refining our previous study (Nature 1986;323:738-742) which covered 52% of the protein. TN peptides made up 31%, and the TR peptides, 34% of the apo B-100 sequence; 23.7% were found under both TN and TR categories. Based on its differential trypsin releasability, apo B-100 can be divided into five domains: 1) residues 1----1000, largely TR; 2) residues 1001----1700, alternating TR and TN; 3) residues 1701----3070, largely TN; 4) residues 3071----4100, mainly TR and mixed; and 5) residues 4101----4536, almost exclusively TN. Domain 1 contained 14 of the 25 Cys residues in apo B. Domain 4 encompassed seven N-glycosylation sites, and contained the putative receptor binding domains. All 19 potential N-glycosylation sites were directly sequenced: 16 were found to be glycosylated and three were not. Three pairs of disulfide bridges were also mapped. Finally, a combination of cDNA sequencing, direct mRNA sequencing, and comparison of published apo B-100 sequences allowed us to identify specific amino acid residues within apo B-100 that seem to represent bona fide allelic variations. Our study provides information on LDL apo B-100 structure that will be important to our understanding of its conformation and metabolism.

Maternal smoking in relation to the incidence of early neonatal jaundice

A case-control study was carried out to investigate the association between maternal smoking during pregnancy and the risk of early neonatal jaundice. A total of 1,569 cases of neonatal jaundice (2.7% of all singleton births) were identified from the 1984 Washington State birth certificates as having a bilirubin level greater than 10 mg/dl within the first 2 days of life. 2,336 nonjaundiced infants were randomly selected to serve as controls. Information regarding smoking during pregnancy was also obtained from the birth certificates. After excluding infants with known risk factors for neonatal jaundice, 912 cases and 1,752 controls were available for analyses. Infants whose mother smoked cigarettes during pregnancy were at lower risk of neonatal jaundice (odds ratio = 0.81; 95% confidence interval = 0.66-0.99) relative to infants of nonsmokers. This relative risk changed very little after adjusting separately for maternal age, infant's gender, number of prior pregnancies, number of prenatal visits, marital status and number of prior fetal deaths. There was suggestive evidence that this apparent protective effect may be operating only among normal and high-birth-weight infants.

Colocalization of GABA and glycine immunoreactivities in a subset of retinal neurons in tiger salamander

Alternate serial 1 micron Durcupan resin sections of tiger salamander retina were stained with antisera against GABA and glycine using postembed immunocytochemical techniques. Although the vast majority of neurons were labeled by either GABA or glycine antiserum, a small percentage of presumed amacrine cells in the inner nuclear layer and cells in the ganglion cell layer were clearly labeled by both antisera, indicative of colocalization of endogenous GABA and glycine. Although there is a greater than 90% chance that a labeled cell will be clearly labeled for either GABA or glycine immunoreactivity, the possibility for cotransmission of two inhibitory transmitters must be considered for a small percentage of these retinal neurons.

Isolation and culture of two cell populations from chick calvaria by density gradient: prostaglandin synthesis by the cells in culture and coculture

In previous studies we demonstrated that PTH stimulates production of prostaglandin E2 (PGE2) by intact chick calvaria. In the present series of experiments, two cell populations were isolated from chick calvaria by centrifugation on a 25%/55% Percoll gradient. Cells harvested from the upper band of the Percoll gradient (designated F-1) appeared large and spindle-shaped in culture. Cells harvested from the lower band of the Percoll gradient (designated F-2) were relatively small and polygonal-shaped. Both cell populations required fetal bovine serum (FBS) for attachment and proliferation. In the presence of FBS the cells formed multilayers, but they formed confluent monolayers in the presence of heat-inactivated FBS. The pattern of cAMP responses to different effectors and biochemical determinations for alkaline and acid phosphatase suggests that the F-2 fraction consists primarily of osteoblasts. No cells with osteoclastic patterns appeared in either fraction. Both cell types synthesized predominantly PGD2. PGE2 was also produced, however, in considerably smaller quantities. PG production in the presence of ionophore A23187 (1 microM) or arachidonate (10 microM) increased significantly when the F-1 and F-2 cells were cocultured at a 1:1 ratio. These results suggest that cell to cell or cell to matrix interactions normally present in intact bone influence PG synthesis.

Localization of putative GABAergic neurons in the larval tiger salamander retina by immunocytochemical and autoradiographic methods

Putative GABAergic neurons in the larval tiger salamander retina were localized by a comparative analysis of glutamate decarboxylase immunoreactivity (GAD-IR), GABA-like immunoreactivity (GABA-IR), and high-affinity 3H-GABA uptake at the light microscopical level. Preliminary data showed that all GAD-IR neurons were double labeled for GABA-IR. However, because the weak somatic labeling with GAD-IR, we could not determine if the converse were true. Neurons commonly labeled with GABA-IR and 3H-GABA uptake include horizontal cells, type I (outer) and type II (inner) bipolar cells, type I (inner) and type II (outer) amacrine cells, and cell bodies in the ganglion cell layer (GCL). In addition, interplexiform cells were identified with GABA-IR. The presence of GABA-IR ganglion cells was indicated by GABA-IR fibers in the optic fiber layer and optic nerve as well as by a GABA-IR cell in the GCL that included a labeled axon. The percentage of labeled somas in the inner nuclear layer (INL) compared to all cells in each layer was similar for the two methods: 30% in INL 1 (outer layer of somas), 15% in INL 2 (middle layer), 43-52% in INL 3 (inner layer), and about 21-26% in the GCL. Labeled processes were found in three bands in the inner plexiform layer, with the densest band located in the most proximal part. Postembedding labeling of 1-micron Durcupan resin sections for GABA-IR showed the same general pattern as obtained with 10-microns cryostat sections, with additional staining, however, of type II (inner) bipolar cell Landolt's clubs. Extensive colocalization of labeling was indicated, and we conclude that GABA-IR can serve as a valid and reliable marker for GABA-containing neurons in this retina and suggest that GABA serves as a transmitter for horizontal cells, several types of amacrine cell, a type of interplexiform cell, and perhaps a small percentage of type I and type II bipolar cells and ganglion cells.

Complete amino acid sequence of the thioesterase domain of chicken liver fatty acid synthase

The complete amino acid sequence of thioesterase domain of chicken liver fatty acid synthase has been determined by sequencing peptides produced by trypsin, Staphylococcus aureus V8 protease, and cyanogen bromide cleavage. The thioesterase domain consists of 300 amino acid residues. All of the tryptic peptides of the thioesterase domain were isolated and sequenced, except the segment covered from position 109 to position 124. Peptides resulting from digestion by Staphylococcus aureus V8 protease and cyanogen bromide cleavage filled the missing part and overlapped the complete sequence of the entire thioesterase domain. The NH2 terminus of the thioesterase domain was determined to be lysine by sequencing the whole domain up to 20 residues while the COOH terminus was identified as serine through carboxyl peptidase Y cleavage. The active site of the thioesterase domain of chicken fatty acid synthase was suggested to be the serine on position 101 according to its homology with other serine-type esterases and proteases which have a common structure of -Gly-X-Ser-Y-Gly- with the variable amino acids X and Y disrupting the homology.

Preparation and characterization of monoclonal antibodies to cephalexin-synthesizing enzyme from Acetobacter turbidans

Eleven monoclonal antibodies against the cephalexin-synthesizing enzyme have been constructed and primarily characterized. These antibodies are all IgG1 type, with medium affinity, and with no enzyme-inhibition effect. They will be utilized as immunoadsorbents to purify their corresponding antigen, the enzyme, in one step.

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.

Exocrine pancreatic enzyme activities and mineral concentrations in SHR/N-corpulent (cp) male rats

Exocrine pancreatic enzyme activities and mineral concentrations were measured in a newly developed congenic strain of corpulent rat (SHR/N-cp). Approximately 4- to 5-wk-old corpulent (cp/cp) and lean (+/?) male rats consumed a diet containing 54% carbohydrate as either cooked cornstarch or 27% cooked cornstarch and 27% fructose for 9.5 mo. After consuming the diet for 3 mo, corpulent rats were hyperinsulinemic, hyperlipidemic and exhibited glycosuria. After consuming the diet for 9.5 mo corpulent rats were twofold heavier and pancreatic weight was 77% that of their lean littermates. Corpulent rats that consumed starch exhibited lower total pancreatic protein with no significant change in total DNA and RNA. In the corpulent rat, both lipase- and chymotrypsinogen-specific activities and both the specific activities and the content of amylase or trypsinogen were lower than those of lean littermates. Fructose consumption resulted in lower pancreatic copper and iron concentrations, and zinc concentration was elevated in corpulent rats. This study suggests that the SHR/N-corpulent rat may be a useful model for studying exocrine pancreatic function in insulin-independent diabetes.

Light microscopic localization of putative glycinergic neurons in the larval tiger salamander retina by immunocytochemical and autoradiographical methods

Putative glycinergic neurons in the larval tiger salamander retina were localized by a comparative analysis of high affinity 3H-glycine uptake and glycine-like immunoreactivity (Gly-IR) at the light microscopic level. Commonly labeled neurons include at least three types of amacrine cell (Type IAd, Type IAb, Type IIAd; distinguished by soma location and dendritic ramification), cell bodies in the ganglion cell layer (GCL), and rarely observed Type II (inner) bipolar cells. With the increased resolution provided by Gly-IR, we identified a Type IAa amacrine cell, two types of Type IIAd amacrine cells, and Gly-IR interplexiform cells. Gly-IR axons in longitudinal sections of the optic nerve indicate the presence of Gly-IR ganglion cells. The percentage of labeled somas in the inner nuclear layer (INL) compared to all cells in each layer was similar for the two methods: 30-40% in INL 2 (middle layer of somas), 30-40% in INL 3 (inner layer of somas), and about 5% in the GCL. Labeled processes were found throughout the full thickness of the inner plexiform layer (IPL), but with a much denser band in the proximal half (sublamina b). The only major difference between the two methods (3H-glycine uptake vs. Gly-IR) was that Type I (outer) bipolar cells were labeled only by 3H-glycine uptake; these cells were more lightly labeled with silver grains than cell bodies in either INL 2 or INL 3. Postembed labeling of 1 micron Durcupan plastic sections for Gly-IR showed the same pattern, but with much higher resolution, as obtained with 10 micron cryostat sections. This study indicates extensive colocalization of labeling by both probes in INL 2, INL 3, the IPL, and the GCL. We conclude that Gly-IR can serve as a valid and reliable marker for glycine-containing neurons in this retina and suggest that glycine serves as a transmitter for several morphologically distinct types of amacrine cell, an interplexiform cell, and perhaps a small percentage of Type II bipolar cells and ganglion cells.

Changes in pancreatic enzyme specific activities of rats fed a high-fructose, low-copper diet

This study describes the progressive changes in exocrine pancreatic enzyme specific activities from rats provided with a diet containing either 62% starch (S) or fructose (F) with 6.0 ppm copper (+Cu) or 0.6 ppm (-Cu) from 21 to 61 days of age. Copper-deficient rats had significantly reduced pancreatic weight and DNA, RNA, protein and copper content and superoxide dismutase (SOD) activity after consuming diet for 39 days. These reductions were far more severe in F-Cu than in S-Cu rats. Copper deficiency significantly reduced pancreatic amylase and lipase specific activities, but the effect was more severe in the F-Cu dietary group. Chymotrypsinogen and trypsinogen specific activities were reduced only in the F-Cu dietary group and the CHO x Cu interaction was significant. High dietary fructose and low dietary copper in combination interact to produce severe reductions in pancreatic amylase, lipase, chymotrypsinogen, and trypsinogen specific activities which could not be explained by either copper deficiency or by an increase in dietary fructose alone.

Human apolipoprotein B: analysis of internal repeats and homology with other apolipoproteins

Apolipoprotein B (apoB) is the major protein component of plasma low density lipoproteins (LDL) and, through its binding to the LDL receptor, it plays a prominent role in lipoprotein metabolism and in the development of atherosclerosis. Specially developed computer programs were applied to detect potential internal repeats in the human apoB sequence and homology of some of these repeats with other apolipoproteins. The simultaneous computer alignment of several (repeated) sequences, carried out in an iterative way to generate consensus sequences, showed the presence of repeated amphipathic helical regions and of repeated hydrophobic proline-rich domains. Extensive Monte-Carlo statistics were used to demonstrate the statistical significance of the internal repeats. Both classes of repeats may contribute to the specific lipid-binding characteristics of apoB. Additional homology, detected between apoB and apoE, the other apolipoprotein-ligand of the LDL receptor, further defined the structural requirements for this receptor-ligand interaction. The computer programs developed in this study should also be useful for detecting internal repeats in other proteins.

Application of convergent beam electron diffraction in the structural study of high-temperature superconducting oxides

Convergent beam electron diffraction (CBED) is a powerful technique for symmetry study of crystal. It has widespread application in physics and material sciences, as demonstrated in a recent superconducting oxide study. Using this technique, we have studied Ba-La-Cu-O superconductors with a transition temperature of about 40 degrees K and Ba-Y-Cu-O superconductors with a critical temperature (Tc) of about 90 degrees K. We have found that in Ba-La-Cu-O superconductors the superconducting phase La2-xBaxCuO4-y has a distorted K2NiF4-type structure and the space group Fmmm. The two other phases in Ba-La-Cu-O superconductors have also been studied. In our Ba-Y-Cu-O superconductors, the Ba2YCu3O7-x compound, which is responsible for 90 degrees K superconductivity, has two different space groups: An orthorhombic space group Pmmm and a tetragonal space group P4mm or P4/mmm.

The complete amino acid sequence of proapolipoprotein A-I of chicken high density lipoproteins

The complete amino acid sequence of proapolipoprotein (proapo) A-I of chicken high density lipoproteins was determined by sequencing overlapping peptides produced by trypsin, S. aureus V8 protease, and cyanogen bromide cleavage. There are 240 amino acid residues in mature chicken apoA-I. By direct sequence analysis of a cyanogen bromide peptide, we also determined the sequence of a 6-amino-acid prosegment which is present at approx. 10% the molar amount of the mature peptide in chicken plasma. Sequence comparison among apoA-I from chicken, human, rabbit, dog and rat, and secondary structure analysis indicate that while the degree of sequence homology is only moderate (less than 50% between chicken and man), there is good conservation of apoA-I secondary structure, especially in the N-terminal two-thirds of the protein in these widely separated species.

Controlled trial of protease inhibitor gabexelate mesilate (FOY) in the treatment of acute pancreatitis

A controlled trial with synthetic protease inhibitor gabexelate mesilate (FOY) in the treatment of acute pancreatitis was conducted in a total of 42 patients. The age, sex, etiology of pancreatitis, initial serum amylase level, and amylase creatinine clearance ratio were comparable between FOY-treated and control groups. FOY did not alter the course of the disease, but there was a weak trend toward lower morbidity and mortality in the FOY-treated patients. These results may justify further, larger scale studies or evaluation of alternate dosage or route of administration.

Apolipoprotein B-48 is the product of a messenger RNA with an organ-specific in-frame stop codon

The primary structure of human apolipoprotein (apo) B-48 has been deduced and shown by a combination of DNA excess hybridization, sequencing of tryptic peptides, cloned complementary DNAs, and intestinal messenger RNAs (mRNAs) to be the product of an intestinal mRNA with an in-frame UAA stop codon resulting from a C to U change in the codon CAA encoding Gln2153 in apoB-100 mRNA. The carboxyl-terminal Ile2152 of apoB-48 purified from chylous ascites fluid has apparently been cleaved from the initial translation product, leaving Met2151 as the new carboxyl-terminus. These data indicate that approximately 85% of the intestinal mRNAs terminate within approximately 0.1 to 1.0 kilobase downstream from the stop codon. The other approximately 15% have lengths similar to hepatic apoB-100 mRNA even though they have the same in-frame stop codon. The organ-specific introduction of a stop codon to a mRNA appears unprecedented and might have implications for cryptic polyadenylation signal recognition and RNA processing.