Characterization of parathyroid hormone fragments produced by cathepsin D

Cleavage of parathyroid hormone by cathepsin D was studied. Four primary products were detected and separated by high performance liquid chromatography. Two of the fragments are fluorescent and therefore contain residue 23 (tryptophan). These fragments are NH2-terminal in origin. The other two cross-react with antisera directed against COOH-terminal portions of the hormone; they are the complementary COOH-terminal fragments. Microsequencing and amino acid analysis showed that the two COOH-terminal fragments are 35-84 and 38-84 bovine parathyroid hormone. By CNBr cleavage and amino acid analysis, the two NH2-terminal fragments were shown to be the complementary 1-37 and 1-34 fragments. The 1-37 fragment is transitory and is rapidly hydrolyzed to 1-34, so that only relatively small amounts are detected at any one time. However, 34-84 was not converted to 38-84, although cleavage at other sites in the COOH-terminal fragments was observed with more exhaustive digestion. The 1-34 fragment appears to be the final product of the action of cathepsin D on parathyroid hormone. Both enzymatically produced NH2-terminal fragments were fully active in the renal membrane adenylyl cyclase assay system.     

Purification of N-terminal hexapeptide of big gastrin from human urine

We previously demonstrated that extremely high amounts of N-terminal big gastrin (G-34) fragments are excreted in human urine and three of them are N-terminal octa-, nona-, and decapeptide of G-34. Our subsequent examination revealed that there exists a considerable amount of another N-terminal G-34 fragment in urine, less hydrophobic than the three peptides. We purified this fragment from urine of an achlorhydric patient and determined the structure: less than Glu-Leu-Gly-Pro-Gln-Gly. The purification was carried out by Sep-Pak C18 cartridges, Sephadex G-25, and reverse phase HPLC. The structure was determined by a combination of amino acid analysis, amino acid sequence analysis, and mass spectral analysis. N-terminal hexapeptide of G-34 is the second richest component of urinary N-terminal G-34 fragments next to N-terminal octapeptide of G-34 in normal subjects.     

Amino acid sequence of the 203-residue fragment of the heavy chain of chicken gizzard myosin containing the SH1-type cysteine residue

A fluorescent fragment of Mr = 23,800 was obtained by the papain digestion of N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylene diamine (abbreviated as IAEDANS)-modified chicken gizzard myosin. The fragment was isolated by gel filtration on a Sephadex G-100 column in the presence of 5 M guanidine-HCl followed by anion exchange chromatography on a QAE Sephadex A-50 column. This fragment contained 203 amino acid residues which could be assigned as a COOH-terminal part of the S-1 heavy chain based on the homology with the known sequence of rabbit skeletal myosin fragment. The amino acid sequence was K-G-M-F-R-T-V- G-Q-L-Y-K-E-Q-L-T-K-L-M-T-T-L-R-N-T-N-P-N-F-V-R-C-I-I-P-N-H-E-K-R-A- G-K-L-D-A-H-L-V-L-E-Q-L-R-C-N-G-V-L-E-G-I-R-I-C-R-Q-G-F-P-N-R-I-V-F-Q- E-F-R-Q-R-Y-E-I-L-A-A-N-A-I-P-K-G-F-M-D-G-K-Q-A-C-I-L-M -I-K-A-L-E-L- D-P-N-L-Y-R-I-G-Q-S-K-I-F-F-R-T-G-V-L-A-H-L-E-E-E-R-D-L-K- I-T-D-V-I-I-A- F-Q-A-Q-C-R-G-Y-L-A-R-K-A-F-A-K-R-Q-Q-Q-L-T-A-M-K-V-I-Q-R-N-C-A -A-Y-L-K-L-R-N-W-Q-W-W-R-L-F-T-K-V-K-P-L-L-Q-V-T-R. The cysteine residue which was modified with IAEDANS was of the SH1 type (Cys-65). Pro-197 was suggested to be the NH2-terminal boundary of the alpha-helical coiled-coil rod sequence of gizzard myosin, based on the homology with the nematode sequence reported by MacLachlan and Karn (Proc. Natl. Acad. Sci. U.S. 80, 4253-4257 (1983)). Three different COOH-terminal peptides (Val-Lys-Pro-Leu-Leu-Gln-Val-Thr-Arg, Val-Lys-Pro-Leu-Leu-Gln, and Val-Lys-Pro-Leu-Leu) were isolated from the tryptic digest of this fragment.(ABSTRACT TRUNCATED AT 400 WORDS)     

COOH-terminal extended endogenous gastrins

Extracts of antral mucosa, gastrinoma tissue and a gastrinoma serum were subjected to Sephadex G-50 high-resolution chromatography monitored by two radioimmunoassays specific for the NH₂- and the COOH-terminal sequence of heptadecapeptide gastrin. Both tissue extracts and serum contained in addition to known NH₂-terminal extended forms also gastrins corresponding to heptadecapeptide gastrin extended at the COOH-terminus. Four COOH-terminal extended gastrins with mean elution constants (K_av) of 0.14, 0.32, 0.44 and 0.49 were encountered. Re-chromatography in urea gradient and tryptic cleavage corroborated their existence. The COOH-terminal extended gastrins are supposed to represent early stages in the modification of the gastrin m-RNA product.     

Urinary immunoreactive gastrin in normal subjects

Gastrin can readily be concentrated from 10 to 50 ml of urine with better than 90% recovery using octadecylsilyl (ODS) silica columns (C18 Sep-Pak cartridge) and then measured by radioimmunoassay. Fractionation on Sephadex G50 gel filtration reveals that the apparent immunoreactivity is not due to nonspecific interference in the assay system but does correspond to the two known forms of gastrin, the 17 and 34 amino acid peptides. Renal clearance of gastrin in 5 normal subjects does not appear to differ in the fasted and fed state and ranged from 0.09 to 0.26 ml/min with an average of 0.16 +/- 0.05 (S.D.) ml/min. Urinary gastrin excretion in the overnight fasting state was generally less than 0.005 pmol/hr/kg body weight and fell to lower levels after a 20-hour fast. Increased urinary gastrin output was observed following feeding. Gastrin output in urine in 7 subjects ranged from 6.8 to 10.2 pmol/24 hr with an average of 8.5 +/- 1.5 (S.D.) pmol/24 hr. A single determination of renal gastrin clearance and 24-hour gastrin urinary output appears to be sufficient for the determination of averaged plasma gastrin levels in normal subjects without renal disease. Similar methodology should be applicable to a variety of other peptidal hormones as well.     

Immunochemical studies on big gastrin using NH2-terminal specific antisera

Methods are described for obtaining antisera specific for the NH₂-terminal regions of human and porcine big gastrin (G34) that can be used in radioimmunoassays. Three antisera have been characterized in detail: one (L66) raised to human 1–15 (Tyr⁷Pro⁸Ser⁹) G34 has an antigenic determinant in the 1–6 region of human G34; a second (L107) raised to 1–19 hG34 has an antigenic determinant in the 1–12 region. Both these antisera react weakly with porcine G34. A third antiserum (L33) raised to porcine G34 has an antigenic determinant in the 1–12 region of this peptide, and reacts weakly with human G34. In human antral extracts fractionated on Sephadex G50. L66 and L107 revealed a minor peak of immunoreactivity corresponding to G34, and a major peak corresponding to the NH₂-terminal tryptic peptide of G34. Concentrations of the latter peptide were closely similar to those of G17 (i.e. the COOH-terminal tryptic peptide of G34), consistent with the idea that G34 is cleaved within G-cells by a trypsin-like enzyme to yield G17. Antiserum L33 revealed small amounts of immunoreactivity in antral extracts of dog and cat, but did not reveal significant immunoreactivity in rat antral extracts. In contrast, L66 reacted with rat antral extracts, but not dog or cat. The sequences of G34 in these species are not known, but the results suggest significant differences compared with human and porcine G34, and indicate a high degree of species-specificity with NH₂-terminal G34 antisera.     

The NH2-terminal and COOH-terminal fragments of dentin matrix protein 1 (DMP1) localize differently in the compartments of dentin and growth plate of bone

Multiple studies have shown that dentin matrix protein 1 (DMP1) is essential for bone and dentin mineralization. After post-translational proteolytic cleavage, DMP1 exists within the extracellular matrix of bone and dentin as an NH2-terminal fragment, a COOH-terminal fragment, and the proteoglycan form of the NH2-terminal fragment (DMP1-PG). To begin to assess the biological function of each fragment, we evaluated the distribution of both fragments in the rat tooth and bone using antibodies specific to the NH2-terminal and COOH-terminal regions of DMP1 and confocal microscopy. In rat first molar organs, the NH2-terminal fragment localized to predentin, whereas the COOH-terminal fragment was mainly restricted to mineralized dentin. In the growth plate of bone, the NH2-terminal fragment appeared in the proliferation and hypertrophic zones, whereas the COOH-terminal fragment occupied the ossification zone. Forster resonance energy transfer analysis showed colocalization of both fragments of DMP1 in odontoblasts and predentin, as well as hypertrophic chondrocytes within the growth plates of bone. The biochemical analysis of bovine teeth showed that predentin is rich in DMP1-PG, whereas mineralized dentin primarily contains the COOH-terminal fragment. We conclude that the differential patterns of expression of NH2-terminal and COOH-terminal fragments of DMP1 reflect their potentially distinct roles in the biomineralization of dentin and bone matrices.     

Identification of gastrin molecular variants in gastrinoma syndrome

The molecular species of gastrin in the circulation and in tumor extracts were studied in two groups of patients: (1) with benign gastrinoma and (2) with gastrinoma with liver metastases. Radioimmunoassays (RIAs) and immunoaffinity chromatography for the amino (NH2)- and amidated COOH-terminus of gastrin-17 (antiserum G17) and the NH2-terminus of gastrin-34 (antiserum G34) were employed. In both benign and metastatic tumors the molecular forms of gastrin in boiling water extracts measured by the gastrin-17 NH2- and COOH-terminal assays were similar. In addition to a molecular component resembling the amidated gastrin-17, there were also significant amounts of larger molecular weight (mol. wt.) forms. The larger mol. wt. forms absorbed by the NH2-terminus of G17 antiserum corresponded to the COOH-terminus-extended forms of gastrin-17. Furthermore, larger mol. wt. gastrins immunopurified by antiserum to the NH2-terminus of gastrin-34 corresponded to gastrin-34 extended molecules. Sera of patients with liver metastases had higher concentrations of the NH2-terminal of gastrin-17 whereas sera of patients with benign gastrinoma contained predominantly gastrins detected by the COOH-terminal assay. These results suggest that: (a) there are differences in the molecular pattern of gastrin in the circulation of patients with benign and metastatic gastrinomas; (b) gastrins which are fully processed with carboxy-terminal amidation predominate in the circulation of patients with benign gastrinoma; and (c) gastrins containing the gastrin-17 and COOH-terminally extended gastrin-17 and gastrin-34 precursor molecules occur in high concentration in the circulation of gastrinoma patients with metastases to the liver.     

Solution structures of human parathyroid hormone fragments hPTH(1-34) and hPTH(1-39) and bovine parathyroid hormone fragment bPTH(1-37)

Parathyroid hormone (PTH) is involved in regulation of the calcium level in blood and has an influence on bone metabolism, thus playing a role in osteoporosis therapy. In this study, the structures of the human PTH fragments (1-34) and (1-39) as well as bovine PTH(1-37) in aqueous buffer solution under near physiological conditions were determined using two-dimensional nuclear magnetic resonance spectroscopy. The overall structure of the first 34 amino acids of these three peptides is virtually identical, exhibiting a short NH(2)-terminal and a longer COOH-terminal helix as well as a defined loop region from His14 to Ser17, stabilized by hydrophobic interactions. bPTH(1-37), which has a higher biological activity, shows a better-defined NH(2)-terminal part. In contrast to NH(2)-terminal truncations, which cause destabilization of helical structure, neither COOH-terminal truncation nor elongation significantly influences the secondary structure. Furthermore, we investigated the structure of hPTH(1-34) in 20% trifluoroethanol solution. In addition to its helix-stabilizing effect, trifluorethanol causes the loss of tertiary hydrophobic interactions.     

Formation and secretion of fragments of parathormone. Identification of cleavage sites

Monolayer cultures of bovine parathyroid cells or fresh gland slices were incubated with radioactive amino acids in order to study the formation and metabolism of parathormone (PTH). PTH, secretory protein I, and COOH-terminal fragments of PTH were all released into media within 30 min, most strongly in the first hour after synthesis. Peptides in tissue, cells, and media were separated using reverse-phase high performance liquid chromatography. In eluates of media, six radioactive peaks were prominent. The first four and the sixth were immunoreactive in a COOH-terminal specific PTH radioimmunoassay, but only the sixth was reactive in an NH2-terminal specific assay. Under conditions where recovery of PTH(1-34) was quantitative, gel filtration of media was used to show that no NH2-terminal fragments of PTH were secreted. Sequence analyses of secreted COOH-terminal peptides indicated that the NH2 termini of the first three peaks corresponded to residues 43, 37, and 34 of PTH. The fourth peak contained a mixture of two peptides with NH2 termini at residues 24 and 28 of PTH. The fifth could not be identified; the sixth was PTH. Cleavages at the 23-24 bond of PTH occurred within minutes of the formation of PTH itself, and the other peptides were formed more slowly. Mandatory cleavage of PTH at the 23-24 peptide bond would destroy the biological activity of the hormone on kidney and bone, a situation consistent with the possibility that intracellular PTH metabolism participates in secretory regulation. The results showed that different peptides were generated in parathyroid cells than were previously shown to be produced by cathepsin B or D. The results suggest that the proteolytic pathway which results in the secretion of PTH fragments is nonlysosomal in nature.     

Cat gastrinoma and the sequence of cat gastrins.

Following the curative resection of a pancreatic gastrinoma in a cat, gastrin peptides were purified from the tissue and sequenced. The sequence of cat gastrinoma G17 (18-34) confirms the previously published sequence. The sequence of cat G34 (1-34) is reported for the first time. The NH2-terminal portion of cat G34 differs from that of dog by having a Q (Gln) for L (Leu) at position 10 from the NH2-terminus.     

Acid-stable trypsin-plasmin inhibitors formed enzymatically from plasma precursor protein

Enzymatic formation of acid-stable trypsin-plasmin inhibitors (ASTPIs) in human plasma with several proteinases, particularly SH-proteinases, was demonstrated. The maximal activity obtained with bromelain was 40 U/ml plasma, which corresponded to about a 10-fold increase as compared to the untreated control plasma (4.2 U/ml). Gel filtration revealed at least two ASTPI activity peaks of molecular weight 16,000 (main peak) and 8000 (minor peak). The main ASTPI was further purified by trypsin-Sepharose affinity chromatography, isoelectric focusing and gel filtration on Sephadex G-75 superfine. The purified inhibitor was found to be identical to the active fragment of plasma ASTPI or urinary trypsin inhibitor (UTI) formed by bromelain treatment. It had an isoelectric point (pI) of 3.7, a molecular weight of 16,000 by SDS-polyacrylamide gel electrophoresis and was a glycine- and glutamic acid-rich protein lacking histidine. The NH2-terminal amino acid sequence was H2N-(Lys)-Glu-Asp-Ser-X-Gln-Leu-Gly-Tyr-Ser-Ala-Gly-Pro-X-Met-Gly-Met-Th r-X-Arg - Tyr-Phe-Tyr-... COOH, which was homologous to the Lys22-Met36 part (or Glu23-Met36 part; 30% of the total) of the plasma ASTPI or UTI molecule (molecular weight 70,000-80,000 by gel filtration). The purified ASTPI displayed the same antigenicity as UTI and exerted strong inhibitory effects on trypsin, chymotrypsin and plasmin amidolysis, but had a much lesser effect on plasmin fibrinolysis. It also strongly inhibited non-plasmic fibrinolysis with human leukocyte proteinase and earthworm proteinase.     

Mapping of the functional domains in the amino-terminal region of calponin.

Three chymotryptic fragments accounting for almost the entire amino acid sequence of gizzard calponin (Takahashi, K., and Nadal-Ginard, B. (1991) J. Biol. Chem. 266, 13284-13288) were isolated and characterized. They encompass the segments of residues 7-144 (NH2-terminal 13-kDa peptide), 7-182 (NH2-terminal 22-kDa peptide), and 183-292 (COOH-terminal 13-kDa peptide). They arise from the sequential hydrolysis of the peptide bonds at Tyr182-Gly183 and Tyr144-Ala145 which were protected by the binding of F-actin to calponin. Only the NH2-terminal 13- and 22-kDa fragments were retained by immobilized Ca(2+)-calmodulin, but only the larger 22 kDa entity cosedimented with F-actin and inhibited, in the absence of Ca(2+)-calmodulin, the skeletal actomyosin subfragment-1 ATPase activity as the intact calponin. Since the latter peptide differs from the NH2-terminal 13-kDa fragment by a COOH-terminal 38-residue extension, this difference segment appears to contain the actin-binding domain of calponin. Zero-length cross-linked complexes of F-actin and either calponin or its 22-kDa peptide were produced. The total CNBr digest of the F-actin-calponin conjugate was fractionated over immobilized calmodulin. The EGTA-eluted pair of cross-linked actin-calponin peptides was composed of the COOH-terminal actin segment of residues 326-355 joined to the NH2-terminal calponin region of residues 52-168 which seems to contain the major determinants for F-actin and Ca(2+)-calmodulin binding.     

Identification and characterization of glycine-extended post-translational processing intermediates of progastrin in porcine stomach

We developed a radioimmunoassay specific for glycine-extended progastrin processing intermediates (G-Gly) using antisera generated against the synthetic peptide Tyr-Gly-Trp-Met-Asp-Phe-Gly. Distribution of immunoreactivity in the porcine gastrointestinal tract obtained with this antibody paralleled that of gastrin with the mucosa containing the highest quantity, 116 +/- 22 pmol/g, wet weight (mean +/- S.E., n = 5), or roughly 4% of gastrin concentration. This immunoreactivity was localized specifically to antral mucosal G-cells by immunohistochemistry. On Sephadex G-50 column chromatography of porcine antral mucosal extracts glycine-extended progastrin processing intermediates were separated into three principal molecular forms, each corresponding to known molecular forms of gastrin, component I, tetratriacontagastrin (G34) and heptadecagastrin (G17). Following purification by antibody-coupled affinity chromatography, one molecular form corresponding to G17 in size was shown to have an amino terminus identical to that of G17. Another molecular form corresponding to G34 in size could be converted to the molecular form corresponding to G17 by tryptic digestion. Our findings indicate that glycine-extended progastrin processing intermediates may serve as immediate precursors for each molecular form of gastrin, thus suggesting an alternative pathway for gastrin biosynthesis more complex than that previously conceived.     

Primary amino acid sequence of follicle-stimulating hormone from human pituitary glands. I. alpha subunit.

Follicle-stimulating hormone of a high state of physicochemical and biological purity was isolated from acetone-preserved human pituitary glands. The follicle-stimulating hormone was dissociated into alpha and beta subunits by treatment with 8 M urea and the subunits were separated by ion exchange chromatography on DEAE-Sephadex A-25. The subunits were freed of undissociated or reassociated follicle-stimulating hormone by gel filtration on Sephadex G-100. For the establishment of the primary amino acid sequence, the alpha subunit was reduced and either carboxyamidomethylated or S-aminoethylated prior to a thermolytic or a tryptic digestion. Each digest was gel filtered on a column of Sephadex G-50 to separate the glycopeptides from the peptides. The glycopeptides and the peptides were purified further by sequential gel filtration on Sephadex G-25, G-15, and Bio-Gel-P-2 and were isolated by high voltage electrophoresis at pH 6, 3.5, and 2. The purity of the isolated peptides was ascertained further by amino acid analysis. The amino acid sequences of the peptides were determined by Edman degradation followed by subtractive amino acid analysis. COOH-terminal sequences were established by digestion with carboxypeptidases A and B. The primary amino acid sequence of human follicle-stimulating hormone-alpha is identical to that of human chorionic gonadotropin-alpha and differs from that of human luteinizing hormone-alpha in having the tripeptide Ala-Pro-Asx- at the NH2-terminal end.     

Identification and characterization of arginine vasopressin-like substances in the rat testis

We have previously demonstrated the suppression of Leydig cell steroidogenesis by arginine vasopressin (AVP) in vitro. Since the circulating level of AVP is too low to mediate a testicular action of this peptide, we have conducted studies to identify testicular AVP-like substances. The supernatant of homogenized, acid-extracted rat testes was found to contain AVP immunoreactivity which showed parallelism with synthetic AVP in a specific radioimmunoassay for AVP. Chromatography of this extract on a Sephadex G-25 column produced three peaks of AVP immunoreactivity. The largest peak eluted close to the column void volume, a second smaller peak eluted at the total column volume, while a third peak co-eluted with synthetic AVP. Following acetone precipitation, ether extraction, and octadecylsilica (C18) adsorption chromatography of the acid extract, the third peak of AVP immunoreactivity (about 600 pg/testis) was fully retained by C18 chromatography and showed parallelism with synthetic AVP in both radioimmuno- and radioreceptor assays. This substance also co-migrated with synthetic AVP on both Sephadex G-25 and reverse-phase thin layer chromatography (RPTLC). The second peak was only partially retained by C18 adsorption chromatography, dilution curves were not parallel with synthetic AVP in radioimmuno- or radioreceptor assay, and this material failed to co-migrate with synthetic AVP on Sephadex G-25 and RPTLC. The first peak of apparent AVP immunoreactivity was associated with an enzyme(s) that degraded labeled AVP. This enzymatic activity, as well as the immunoreactivity, could be eliminated by heating the extract to 90 degrees C. These results demonstrate, by a number of independent criteria, that rat testes contain a substance which behaves like authentic AVP. Due to its high concentration, the AVP-like peptide may be synthesized or concentrated by testis cells. In addition, testis tissue contains enzymatic activity which degrades AVP and could represent a site of regulation of AVP action. Coupled with the previously demonstrated testis action of AVP, these results suggest a paracrine or autocrine role of the neurohypophysial hormone at the testis level.     

Effects of tilting and volume loading on plasma levels and urinary excretion of relaxin, NT-pro-ANP, and NT-pro-BNP in male volunteers.

The polypeptide relaxin (RLX) has been suggested to play a role in cardiorenal integration and to be related to the natriuretic peptide system. We hence examined the effects of variations in thoracic blood volume and intravenous volume loading on plasma and urinary RLX levels and associated changes in natriuretic peptide levels in healthy men. Two groups of eight subjects were randomly tilted into a 15 degrees feet-down or a 15 degrees head-down position. Ten volunteers were crossover subjected to an infusion of 15 ml/kg of 0.9% NaCl (over 60 min) or control during an observation period of 10 h. Blood and urine were sampled at timed intervals. RLX, NH(2)-terminal prohormones of atrial natriuretic peptide (NT-pro-ANP), and NH(2)-terminal prohormones of brain natriuretic peptide (NT-pro-BNP) were determined by enzyme, radio-, and electrochemoluminescence immunoassays, respectively. NT-pro-ANP levels (in percentage of baseline levels) were higher (P < 0.05) during the head-down (124 +/- 13%) than during the feet-down position (82 +/- 6%). NT-pro-BNP and RLX were not affected by tilting. Volume loading induced a short-lasting increase in plasma NT-pro-ANP, a delayed increase in plasma NT-pro-BNP, had no effect on plasma RLX, and induced a parallel increase in urine flow, renal excretion of sodium, RLX, and NT-pro-BNP. It is concluded that variations in thoracic blood volume in healthy men are not associated with variations in plasma RLX. Increased urinary RLX and NT-pro-BNP excretion during volume loading suggest renal production and a possible role of kidney-derived RLX and brain natriuretic peptide in sodium homeostasis in men.     

Comparison of huntingtin proteolytic fragments in human lymphoblast cell lines and human brain

Proteolytic fragments of huntingtin (htt) in human lymphoblast cell lines from HD and control cases were compared to those in human HD striatal and cortical brain regions, by western blots with epitope-specific antibodies. HD lymphoblast cell lines were heterozygous and homozygous for the expanded CAG triplet repeat mutations, which represented adult onset and juvenile HD. Lymphoblasts contained NH(2)- and COOH-terminal htt fragments of 20-100 kDa, with many similar htt fragments in HD compared to control lymphoblast cell lines. Detection of htt fragments in a homozygous HD lymphoblast cell line demonstrated proteolysis of mutant htt. It was of interest that adult HD lymphoblasts showed a 63-64 kDa htt fragment detected by the NH(2)-domain antibody, which was not found in controls. In addition, control and HD heterozygous cells showed a common 60-61 kDa band (detected by the NH(2)-domain antibody), which was absent in homozygous HD lymphoblast cells. These results suggest that the 63-64 kDa and 60-61 kDa NH(2)-domain htt fragments may be associated with mutant and normal htt, respectively. In juvenile HD lymphoblasts, the presence of a 66-kDa, instead of the 63-64 kDa N-domain htt fragment, may be consistent with the larger polyglutamine expansion of mutant htt in the juvenile case of HD. Lymphoblasts and striatal or cortical regions from HD brains showed similarities and differences in NH(2)- and COOH-terminal htt fragments. HD striatum showed elevated levels of 50 and 45 kDa NH(2)-terminal htt fragments [detected with anti(1-17) serum] compared to controls. Cortex from HD and control brains showed similar NH(2)-terminal htt fragments of 50, 43, 40, and 20 kDa; lymphoblasts also showed NH(2)-terminal htt fragments of 50, 43, 40, and 20 kDa. In addition, a 48-kDa COOH-terminal htt band was elevated in HD striatum, which was also detected in lymphoblasts. Overall, results demonstrate that mutant and normal htt undergo extensive proteolysis in lymphoblast cell lines, with similarities and differences compared to htt fragments observed in HD striatal and cortical brain regions. These data for in vivo proteolysis of htt are consistent with the observed neurotoxicity of recombinant NH(2)-terminal mutant htt fragments expressed in transgenic mice and in transfected cell lines that may be related to the pathogenesis of HD.     

Isolation of human erythropoietin with monoclonal antibodies

Human erythropoietin was isolated from urine of aplastic anemic patients in a high yield with a simple purification procedure using an immunoadsorbent column of monoclonal antibodies and a Sephadex G-100 column. About 6 mg of erythropoietin was isolated from 700 liters of urine and the specific activity was estimated to be 81,600 units/mg of protein with an in vivo 59Fe incorporation assay method, using starved rats. Activity measurement of the extracts from sliced gels after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the Western blotting technique revealed heterogeneity of the isolated erythropoietin, which is probably caused by variable amounts of carbohydrates attached to the polypeptide chain. Thirty amino acids in the NH2-terminal portion of the isolated hormone were sequenced.     

Limited pepsin digestion of human plasma albumin.

Limited pepsin digestion of human plasma albumin at pH 3.5 and 0 degrees in the presence of octanoate caused cleavage at residue 307 of the albumin molecule to yield two fragments. Thw two fragments corresponding to the NH2- and the COOH-terminal halves of the molecule were isolated in yields of about 15%. The COOH-terminal fragment is a mixture in which about 85% of the molecules had an additional cleavage at residue 422 of the albumin molecule. The COOH-terminal fragment with the additional cleavage at residue 422 contains two peptides which are linked by a disulfide bridge at residues 391 and 437 of the albumin molecule. Both the NH2- and the COOH-terminal fragment of human albumin showed no detectable binding of octanoate anions, that is, less than 1/170 of the binding constant of the primary site of human albumin. These findings differ from earlier observations on limited pepsin digestion of bovine plasma albumin where the corresponding COOH-terminal fragment had the octanoate-binding activity, about 1/8 of the primary binding constant of bovine albumin, while the NH2-terminal fragment did not. The COOH-terminal fragment of bovine albumin did not have cleavage at residue 422 as in the corresponding fragment of human albumin. However, it is not clear that the loss of octanoate-binding activity of fragment C of human albumin is a direct consequence of the cleavage at residue 422.