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Results for “Protein Precursors”

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At least 19 recordsLinked to original sources
PubMed1976

Biosynthesis of albumin via a precursor protein in Morris hepatoma 5123tc.

The mechanism of albumin biosynthesis was studied in Morris hepatoma 5123tc in vivo and in hepatoma cell suspensions obtained by solubilizing the intercellular matrix with collagenase and hyaluronidase. In the in vivo experiments, L-[-14C]leucine was injected i.v. into rats bearing hepatomas in the muscles of both hind legs. After 14 min, tumors were removed and homogenized. A protein fraction quantitatively precipitable with antialbumin was isolated from the homogenate by acetone fractionation and precipitation with antiserum against serum albumin. This protein fraction was not homogeneous. With the use of 3 consecutive chromatographies on diethylaminoethyl cellulose, a very highly radioactive albumin-like protein could be separated from a large amount of only slightly radioactive albumin. In hepatoma cell suspensions incubated with L-[1-14C]leucine followed by a chase with excess nonradioactive L-leucine, radioactivity was incorporated first into the albumin-like protein and transferred thereafter into albumin, suggesting that albumin was synthesized via the albuminlike protein as precursor. In vivo, 1.8% of newly synthesized hepatoma protein was albumin or its precursor, compared with 1.2% in cell suspensions.

Albumins↗
PubMed1991

Segregation of a missense mutation in the amyloid precursor protein gene with familial Alzheimer's disease.

A locus segregating with familial Alzheimer's disease (AD) has been mapped to chromosome 21, close to the amyloid precursor protein (APP) gene. Recombinants between the APP gene and the AD locus have been reported which seemed to exclude it as the site of the mutation causing familial AD. But recent genetic analysis of a large number of AD families has demonstrated that the disease is heterogeneous. Families with late-onset AD do not show linkage to chromosome 21 markers. Some families with early-onset AD show linkage to chromosome 21 markers, but some do not. This has led to the suggestion that there is non-allelic genetic heterogeneity even within early onset familial AD. To avoid the problems that heterogeneity poses for genetic analysis, we have examined the cosegregation of AD and markers along the long arm of chromosome 21 in a single family with AD confirmed by autopsy. Here we demonstrate that in this kindred, which shows linkage to chromosome 21 markers, there is a point mutation in the APP gene. This mutation causes an amino-acid substitution (Val----Ile) close to the carboxy terminus of the beta-amyloid peptide. Screening other cases of familial AD revealed a second unrelated family in which this variant occurs. This suggests that some cases of AD could be caused by mutations in the APP gene.

Alzheimer Disease↗
PubMed1976

The effect of aflatoxins on the incorporation of RNA and protein precursors by isolated hepatocytes.

Hepatocytes prepared by a simplified enzymatic technique were active in the incorporation of RNA and protein precursors into acid-insoluble material. The incorporation of RNA precursors was very markedly inhibited by low levels of aflatoxin B1 and G1 but not by aflatoxins B2 and G2. The activity of mixed function oxidases (MFO), the drug-metabolizing system of the endoplasmic reticulum, could be suppressed in these cells by SKF525A or stimulated by NADPH. SKF525A caused a reduction in the inhibition by aflatoxin B1 of the incorporation of RNA precursor into macromolecules. This finding suggests that a metabolite of aflatoxin B1 is the actual inhibitor of RNA synthesis in the cells. Measurement of lactate dehydrogenase activity showed these cells to be leaky on incubation at 37 degrees C and thus not suitable for studies of protein secretion.

Aflatoxins↗
PubMed1979

Identification of chorion protein precursors and the mRNAs that encode them in Drosophila melanogaster.

Specific antisera were generated for major size classes of Drosophila chorion proteins. These antisera were used in conjunction with cell-free translation of follicular RNA to identify precursors, containing signal peptides, for chorion components A1, A2, B1, and B2. An additional precursor cross-reacts with anti-B antisera, although its product appears to correspond to a protein distinct from authenic B proteins. The size classes of mRNA encoding A and B protein precursors have been identified by cell-free translations.

Animals↗
PubMed1975

Identification of a precursor protein to the major glycoproteins of mouse mammary tumor virus.

Mouse mammary tumor virus-producing cultures of mouse mammary tumor cells synthesize a viral-related polypeptide of molecular weight of 73,000 (gp 73) which is rapidly labeled during a short pulse but disappears during the chase concomitantly with the appearance of label in the virion glycoproteins gp 49 and gp 37.5/33.5. The addition of the protein synthesis-inhibitor cycloheximide to the chase medium has little effect on this conversion. Treatment of the proposed precursor with alpha-chymotrypsin leads to the formation of a polypeptide of molecular weight 49,000, similar to the major virion glycoprotein. A comparison of tryptic digest maps of the glycoproteins involved supports the hypothesis that both the viral glycoproteins gp 49 and gp 37.5/33.5 are derived from gp 73.

Animals↗
PubMed1978

[Procaine, a local anesthetic, interacting with the cell membrane and inhibiting the processing of exported protein precursors in Escherichia coli].

In E. coli cells grown in the presence of procaine (0.55% w/v), precursor forms of alkaline phosphatase and of glutamine binding protein accumulate besides mature forms synthesized prior to procaine addition. An experimental technique, of general application, for isolation and purification of mature and precursor forms obtained under these conditions, is described.

Alkaline Phosphatase↗
PubMed1979

Capsid protein precursor is one of two initiated products of translation of poliovirus RNA in vitro.

Previous studies in our laboratory have demonstrated that cell-free systems translating the Mahoney strain of poliovirus type I RNA utilize two unique initiation sites. In this study, defective-interfering particles of poliovirus, which contain deletions in the region encoding the capsid proteins, are shown to initiate translation of proteins in vitro at these same two sites. Both the standard virus and the defective-interfering virus RNA direct the synthesis of two polypeptides labeled with n-formyl-methionine (fmet) at their amino termini. The size of the smaller fmet polypeptide synthesized in vitro by the defective virus appears identical in size to that of the standard virus. However, the larger-molecular-weight fmet polypeptide is reduced in size from 115,000 to 69,000 daltons. This correlates exactly with the reduced size of the precursor to the capsid proteins synthesized by the defective virus in vivo and with the size of the deletion in the defective virus RNA (1,200 bases). This provides genetic evidence that the 115,000-dalton fmet polypeptide synthesized into vitro by the standard virus is NCVP1a, the precursor to the coat proteins. Although the identity of the small (5,000 to 10,000 daltons) fmet polypeptide is not clear, several lines of evidence enable us to exclude the possibility that it is VP4, the smallest viral capsid protein.

Capsid↗
PubMed1979

Presence in human epidermal cells of a soluble protein precursor of the cross-linked envelope: activation of the cross-linking by calcium ions.

Late in the terminal differentiation of epidermis and cultured epidermal cells, a protein envelope located beneath the plasma membrane becomes cross-linked by cellular transglutaminase. The process of cross-linking can be initiated in cultured epidermal cells by agents affecting cell membrane permeability--nonionic detergents, high salt concentrations and ionophores. These agents initiate the cross-linking process by making calcium ions available to the transglutaminase. A soluble precursor of the cross-linked envelope has been identified in crude extracts of cultured epidermal cells by its ability to incorporate labeled amines through the action of transglutaminase. The protein has been purified to homogeneity by gel filtration and chromatography on columns of DEAE-cellulose and hydroxyapatite. Comprising an estimated 5--10% of the soluble cell proteins, it has a molecular weight of about 92,000, is isoelectric at pH 4.5 +/- 0.3 and has an unusual amino acid composition (46% Glx residues). It is chemically and immunochemically unrelated to keratins. The following evidence confirms that the protein becomes incorporated into cross-linked envelopes: first, washed cross-linked envelopes bind antibody to the purified protein, as shown by indirect immunofluorescence; second, absorption of the antiserum with washed envelopes removes all detectable antibodies to the purified protein; and third, the protein cannot be extracted from keratinocytes after their envelopes have become cross-linked. Examination of sections of epidermis by immunofluorescence, using antiserum to the purified protein, reveals that in addition to the stratum corneum, the living cells of the outer half of the spinous layer react strongly. The envelope precursor is present in the cytoplasm, but becomes concentrated at the cell periphery, where it will be cross-linked later, when the cells have passed through the granular layer. The protein is also concentrated in a peripheral location in cultured epidermal cells.

Amino Acids↗
PubMed1978

Gycoprotein and protein precursors to plasma membranes in vesicular stomatitis virus infected HeLa cells.

Vesicular stomatitis virus is known to mature at HeLa cell plasma membranes. To study the process, cells, infected with vesicular stomatitis virus, were fractionated after short term labeling studies (1 min pulse, 1 min chase) to determine the assembly kinetics of G protein and M protein into plasma membranes. Newly synthesized M protein was found released in the supernatant from which free polysomes were sedimented during sucrose gradient analysis of these polysomes. If this M protein is particle bound, it must have a density of less than 1.08 g/ml. About 40% of this M protein so labeled was not sedimentable at 165,000 X g for 16 h. This newly synthesized M protein had not yet assembled into plasma membrane and thus must represent an internal pool. This and previous studies show that it has a subsequent transit time to the plasma membrane of about 2 min. Once associated with plasma membranes, M protein decayed in an approximately logarithmic fashion indicating that newly synthesized M randomly mixes (and turns over) with preexisting M protein. G protein was particle bound in a 1 min pulse, 1 min chase, and was never found released in a soluble form. At the later time when fucose is added to G protein, the oligosaccharide moiety is near to complete, and on completion is about 2,000 in molecular weight. Evidence is presented showing that fucose is probably attached to the N-acetylglucosamine of the protein carbohydrate linkage. G protein to which fucose had just been added was located internally on a membranous fraction of density 1.14 g/ml in sucrose; its subsequent transit time from this pool (which in uninfected cells is between 1--2% of the total cell fucosyl glycoprotein) was about 15 min. Because their densities were different and their transit times were different, internal newly synthesized M and fucosyl G protein which assemble into plasma membranes were not on the same internal membranous component. Association of M protein with the plasma membranes may thus occur from a nonsedimentable soluble cytoplasmic pool by a process of direct adsorption.

Cell Membrane↗
PubMed1976

Effect of "restricted ovulator" gene on uptake of yolk-precursor protein.

The bulk of the yolk proteins and lipoproteins constituting the yolks of mature oocytes in birds are synthesized by the liver and transported via the plasma to the oocytes where they are incorporated by micropinocytosis. Evidence is presented indicating that oocytes of hens possessing a mutation identified by Jones, Briles, and Schjeide as a "restricted ovulator gene" fail to incorporate normal amounts and proportions of low density lipoproteins, lipovitellin and possible other proteins making up the bulk of the yolk material. Plasma albumin is taken into the yolks but the other proteins synthesized by the liver for deposition within the oocytes accumulate in the plasma, attaining very high levels. The possible nature of the "lock" preventing normal deposition of the excluded yolk proteins is discussed.

Animals↗
PubMed1978

In vitro prothrombin synthesis from a purified precursor protein. II. Partial purification of bovine carboxylase.

In this paper, we describe the isolation and partial purification of an enzyme system that converts bovine decarboxyfactor II (PIVKA-II) into prothrombin (factor II). It is shown that the increase in factor II activity occurs in parallel with 14CO2 incorporation into BaSO4 adsorbable proteins. The system is not strictly vitamin K-dependent because it is obtained from the livers of normal healthy cows. By preincubating the enzyme(s) with an excess of warfarin, an absolute vitamin K1-dependence can be obtained. The reaction is inhibited by its own product, factor II.

Animals↗