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J Burnside

Publications and source records attributed to J Burnside.

At least 19 recordsLinked to original sources
PubMed1995

Comparison of gene expression in normal and growth hormone receptor-deficient dwarf chickens reveals a novel growth hormone regulated gene.

Because of a dysfunctional growth hormone (GH) receptor there is an absence of GH-dependent gene expression in the sex-linked dwarf chicken. Therefore, a comparison of mRNAs expressed in normal and dwarf chickens should lead to the identification of mRNAs that are regulated by GH action. We have compared gene expression in normal and dwarf chickens using the mRNA differential display technique. A combination of three anchored oligo dT primers and 15 random decamers were used to detect at least 75 differentially expressed mRNAs. One of these, designated GHRG-1, hybridizes to a 0.9 kb transcript found only in liver and in normal chickens shows a pattern of developmental expression which parallels the plasma GH profile. A GHRG-1 cDNA clone was isolated that encodes a 120 amino acid peptide with no homology to any known gene. Sequence of the promoter from a genomic clone shows a region with strong similarity to the GH response element identified in the serine protease inhibitor gene, Spi 2.1. These results suggest that GHRG-1 is a novel GH regulated gene.

Aging↗
PubMed1995

The Australian Capital Territory Injury Surveillance and Prevention Project.

OBJECTIVE: To identify the representativeness and sensitivity of the data collected by the Australian Capital Territory Injury Surveillance and Prevention Project (ACTISPP) for ED injury cases seen in the Australian Capital Territory (ACT). METHODS: A retrospective descriptive study was conducted using a systematic sample of people injured in the ACT between January 20 and September 19, 1992, and who received their first treatment for this injury in an ACT ED. The ACTISPP surveillance system is dependent on ED patient or family completion and return of a comprehensive injury survey. The following population variables in the ACTISPP database were compared with those of the injured ED population, as determined by ED and hospital record review: age, gender, postal code of residence, nature of injury, body part injured, and whether the patient had been admitted to hospital. RESULTS: The sensitivity of the surveillance system for injuries seen in the ED was 31% (95% CI = 30-32%). The distribution of the ACTISPP sample did not differ from the expected distribution for sex or socioeconomic status. The distributions differed by age only in the 5-14-year age group (p < 0.001). With respect to the nature of injury and body part injured, the difference was significant (p < 0.001) but was no greater than 7% for any of the categories. Two percent of the surveillance sample were admitted to hospital, compared with an estimated 4% of the target population (p < 0.001). CONCLUSIONS: Approximately one-third of all incident injuries managed in the EDs of the ACT are included in the ACTISPP database. Although some sampling bias is introduced in the surveillance process, it does not appear to be of sufficient magnitude to compromise the project's goals.

Adolescent↗
PubMed1992

Abnormal growth hormone receptor gene expression in the sex-linked dwarf chicken.

Sex-linked dwarfism is a recessive mutation that causes a reduction in body weight gain and long bone growth of chickens. We examined the effect of the dwarfing gene on body weight, hepatic GH-binding activity, and the structure and expression of the growth hormone receptor (GHR) gene in two different lines of sex-linked dwarf (SLD) broiler chickens. Liver samples from one line of dwarf chicken were obtained from Arbor Acres Farm, Inc. (Glastonbury, CT) and fertile eggs from the second line of SLD were obtained from the University of Georgia. In the GA line, the average body weight of homozygous (dwdw) males at 11 weeks of age was 43% lower than that of normal (DwDw) males, while heterozygous (Dwdw) males were only 9% below normal. In the CT line, hepatic GH-binding activity of 35-week-old chickens was high (20% specific binding) in normal (DwDw) males and undetectable in liver membranes prepared from dwdw males. At 11 weeks of age, hepatic GH-binding activity of Dwdw males (3.9% specific binding) in the GA line was reduced by 44% and that of dwdw males was almost undetectable (0.34% specific binding) when compared to the average of normal GA males (7.1% specific binding). Southern and Northern blot analyses revealed different abnormalities in the GHR gene from the two separate lines of SLD. A restriction fragment length polymorphism in DNA and an aberrantly sized transcript (mRNA) were detected in the CT line of SLD chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Developmental expression of hepatic growth hormone receptor and insulin-like growth factor-I mRNA in the chicken.

We have examined the ontogeny of expression of growth hormone (GH) receptor (GHR) and insulin-like growth factor-I (IGF-I) mRNA in chicken liver from day 13 of incubation until 31 weeks of age. The profiles of GHR and IGF-I mRNA levels were compared to developmental changes in body weight and plasma levels of GH and IGF-I. In the embryo, hepatic GHR mRNA was not detectable until day 15, highest on days 17 and 19, and then declined at hatching (day 21). Following an initial 2-week delay after hatching, there was a progressive increase in hepatic GHR mRNA which continued after the birds reached mature body weight. Plasma GH reached peak levels at 3-4 weeks of age and then fell sharply until maintenance of a low basal level after 10 weeks of age. Thus, there appears to be a strong inverse relationship between expression of the GHR and basal plasma GH levels in the prepubertal chicken. Although IGF-I mRNA was undetectable in embryonic liver by Northern blot analysis, there is a good correlation between expression of hepatic IGF-I mRNA and the plasma IGF-I profile during post-hatching development in the chicken. The highest levels of IGF-I mRNA were reached at 4 weeks of age which was followed by a slow decline to the basal levels maintained after 10 weeks of age. It appears that the decline in plasma IGF-I lags considerably behind the sharp fall in plasma GH levels and expression of hepatic IGF-I mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Molecular cloning of the chicken growth hormone receptor complementary deoxyribonucleic acid: mutation of the gene in sex-linked dwarf chickens.

A novel complementary DNA (cDNA) encoding the chicken GH receptor was isolated from a chicken liver cDNA library, using polymerase chain reaction with primers derived from highly conserved sequences of the mammalian GH receptor. The nucleotide sequence predicts a mature protein of 592 amino acids and a 16 amino acid signal peptide that are partially homologous to the sequence reported for the rabbit (53%), rat (58%), and human (50%) GH receptors. Despite this low level of homology, a number of structural features of the GH receptor are conserved, including 7 cysteine residues in the extracellular domain and 5 in the intracellular region. Three transcripts of approximately 4.7, 4.0, and 1.0 kilobases are present on Northern blots of total RNA prepared from the livers of 35-week-old male chickens. Expression of the GH receptor was also detected in a wide range of tissues. The chicken GH receptor cDNA was then used as a probe in Southern and Northern blot analyses of DNA and RNA prepared from livers of sex-linked dwarf chickens, which have undetectable levels of hepatic GH-binding activity, in addition to other endocrine abnormalities. A restriction fragment length polymorphism was found in DNA, and an aberrantly-sized transcript was found in hepatic RNA of the dwarf chicken. These results indicate that a mutation in the GH receptor gene is responsible for the phenotype of the sex-linked dwarf chicken. This type of dwarfism resembles Laron-type dwarfism in humans, where a defect in the GH receptor gene has recently been identified. These receptor-deficient chickens should serve as a unique model system for studying the role of the GH receptor in growth and development.

Amino Acid Sequence↗
PubMed1991

3,5,3'-triiodothyronine (T3) receptor-auxiliary protein (TRAP) binds DNA and forms heterodimers with the T3 receptor.

Nuclear factors enhance binding of T3 receptors (TR) to DNA, suggesting that T3 action may require a multicomponent complex bound to thyroid hormone response elements (TREs). We refer to the 65,000 Da nuclear protein in GH3 cells that enhances TR binding to DNA as the TR-auxiliary protein (TRAP) and have characterized its interaction with TR. Using a TRE-DNA affinity matrix we show that TRAP is able to bind to DNA, even in the absence of functional TR. We then used carboxyl-terminal truncations of rat TR alpha-1 and human TR beta in the avidin-biotin complex DNA-binding assay to identify regions that are important for interaction with TRAP. Removal of 34 residues of hTR beta abolishes T3-binding activity, but the ability to bind TRAP is retained. Further truncations and point mutations suggest that TRAP interacts with the ligand-binding domain of TR and with an independent region which overlaps a conserved sequence adjacent to the second Zn2+ finger (amino acids 120-149 in rTR alpha-1). A fragment of rTR alpha-1 (alpha C291) which encompasses these two regions inhibits the ability of TRAP to enhance TR binding to DNA. This is due to binding of alpha C291 to TR, demonstrating the ability of TR to form homodimers. The inability of TRAP to interact with TR dimers and the similarity of the locations of the estradiol receptor dimerization domains with the TRAP interaction regions lead us to conclude that TRAP stabilizes TR binding to DNA by formation of TRAP-TR heterodimers with both proteins bound to the DNA. TR bound to the estrogen response element is unable to respond to TRAP and unable to stimulate transcription, possibly due to the absence of TRAP in the TR-estrogen response element complex. In addition, TRAP may interact with a certain subset of the nuclear receptor superfamily, since human retinoic acid receptor-beta and vitamin D receptor show increased binding to TREs in the presence of nuclear extract, but c-erbA alpha-2, a variant TR, does not respond to TRAP.

Animals↗
PubMed1990

A nuclear factor that enhances binding of thyroid hormone receptors to thyroid hormone response elements.

Recent studies from this laboratory have demonstrated the presence of thyroid hormone response elements (TREs) in the 5'-flanking region of the rat alpha and TSH beta subunit genes. Using an avidin-biotin complex DNA binding assay, we have shown that these TREs bind the thyroid hormone (T3) receptor present in nuclear extracts of GH3 cells, as well as the in vitro synthesized Hc-erbA beta, which has been identified as a member of the family of T3 receptors. The binding of Hc-erbA beta to the alpha subunit TRE can be enhanced 3-4-fold by including GH3 nuclear extract in the binding assay. Binding to the TRE present in the TSH beta gene or the rat growth hormone gene was similarly enhanced, although to a lesser degree. The enhanced binding activity is trypsin-sensitive and heat labile, and is not reproduced by the addition of histones, bovine serum albumin, or cytosol instead of nuclear extract. Gel exclusion chromatography suggests a molecular size of approximately 65,000 Da. This protein, which is present in several different cell types, is also able to complement binding of the rat erbA alpha-1 and the pituitary-specific erbA beta-2 forms of the receptor. These data suggest that the binding of the T3 receptor to a TRE is augmented by another nuclear protein, which may be involved in the mechanism of action of thyroid hormone.

Animals↗
PubMed1989

Thyroid hormone regulation of the rat glycoprotein hormone alpha-subunit gene promoter activity.

An important physiological control of the glycoprotein hormone alpha-subunit is the negative feedback by thyroid hormones in the thyrotrope. A region of the rat glycoprotein hormone alpha-subunit gene that is involved in transcriptional regulation by thyroid hormone has been identified by transient transfection studies, and sequence-specific binding of the thyroid hormone receptor to a site within this region has been demonstrated. Deletion-mutation studies using plasmid expression vectors containing either 246, 170, or 80 base pairs of the 5'-flanking region of the rat alpha-subunit gene fused to the coding region of the bacterial chloramphenicol acetyltransferase gene demonstrate 3,5,3'-triiodo-L-thyronine (T3)-regulated expression in GH3 cells, a T3-responsive somatotrophic cell line. In order to investigate the possibility of thyroid hormone receptor interaction with this segment of the rat alpha-subunit gene, the binding of the thyroid hormone receptor to synthetic oligodeoxynucleotides was analyzed using an avidin-biotin complex DNA binding assay. An oligodeoxyribonucleotide representing a fragment of the alpha-subunit gene from -74 to -38, relative to the transcriptional start site, shows significant binding to [125I]T3-receptor complex present in nuclear extracts of GH3 cells. This fragment binds receptor to a degree similar to that seen with a fragment of the rat growth hormone gene which contains a putative thyroid hormone-responsive element. In addition, this fragment of the rat alpha-subunit gene binds to the in vitro synthesized human c-erbA beta protein, which has been identified as a member of the family of putative T3 receptors. These data demonstrate that a cis-active thyroid hormone-responsive element resides in the 5'-flanking region of the rat alpha-subunit gene and that the mechanism involved in the suppression of expression of this gene by T3 could involve specific binding of the thyroid hormone receptor to this region of the gene.

Animals↗
PubMed1989

Thyroid hormones regulate rat thyrotropin beta gene promoter activity expressed in GH3 cells.

Thyroid hormones suppress the synthesis of TSH in part by decreasing the rate of alpha and TSH beta gene transcription. Cis-acting DNA sequences present in the rat TSH beta subunit gene that are induced in transcriptional regulation by thyroid hormone have been identified by deletion-mutation and transient expression studies. Plasmid expression vectors were constructed including 2900, 900, 204, 77, 17 base pairs (bp) of 5'-flanking sequence and exon (5'-untranslated sequence, transcriptional start sites) fused to the coding region of the bacterial chloramphenicol acetyltransferase (CAT) gene. The transfected chimaeric plasmids demonstrated expression (with TSH beta DNA sequences in the 5'- to -3'-but not 3'- to -5'-orientation) in both a clonal pituitary cell line, GH3, and primary pituitary cell cultures, both of which are responsive to thyroid hormones. T3 (10(-11) M to 10(-7) M) treatment of transfected cells produced a dose-dependent decrease in CAT expression with a maximal 70% decrease at 10(-8) M. While a decrease in the basal level of expression was noted with progressive removal of both 5'-flanking and intronic sequences adjacent to exon 1, the fold-decrease in response to T3 was equivalent even in the 57 bp construct. In contrast, T3 had no effect on CAT expression directed by the promoter of the herpes simplex virus thymidine kinase gene. Thus, the rat TSH beta gene 5'-flanking region can direct heterologous gene expression in GH3 cells and contains sequences which have properties of a putative cis-active T3 responsive regulatory element(s).2+he

Animals↗
PubMed1989

Thyrotropin-releasing hormone stimulates the activity of the rat thyrotropin beta-subunit gene promoter transfected into pituitary cells.

In order to investigate the molecular mechanism(s) by which TRH regulates the biosynthesis of TSH, we are studying the effects of TRH on the expression of the TSH subunit genes (alpha and TSH beta). To study the structure-function relation of TRH stimulation of the activity of the single rat TSH beta gene, chimaeric plasmids were constructed. The 5'-flanking region of the rat TSH beta gene including exon 1 (5'-untranslated region) was inserted into a promoterless, modified pBR, chloramphenicol acetyltransferase (CAT) expression vector. After transfection, specific TSH beta promoter activity was evident in both TRH-responsive pituitary-derived GH3 and primary pituitary cell cultures. To determine potential regulation of TSH beta promoter-directed activity in these cells by TRH, cells were incubated with media containing TRH (10(-7) to 10(-11) M) for 1 to 48 h. TRH stimulated a 1.5- to 3-fold increase in TSH beta promoter activity. Concomitant with an increase in CAT activity was an anticipated increase in PRL synthesis in the GH3 cells in response to TRH. The TRH effect on the TSH beta gene was specific; no increase in CAT activity was detected for TKCAT (thymidine kinase of herpes simplex virus promoter), pBRCAT (no promoter), or TSH beta CAT (3'-5'-orientation). Similar results were obtained using primary pituitary cell cultures. Deletion mutation analysis indicated that TRH sensitivity was detected in a 1.1 kilobase, but not in a 0.38 kilobase TSH beta gene fragment suggesting that the TRH responsive element(s) resides at least in part within the 700 base pairs of the 5'-flanking sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Binding of thyroid hormone receptors to the rat thyrotropin-beta gene.

Negative regulation of rat TSH beta gene expression by thyroid hormone is mediated largely by decreased transcription of the gene. This is apparently mediated by a cis-acting element which has been localized to a 57-basepair fragment spanning the second transcriptional start site of the rat TSH beta gene. We have investigated whether thyroid hormone receptors bind specifically to DNA sequences in this region of the gene. We compared binding of native T3 receptor to the TSH beta gene sequences and to the rat GH (rGH) gene T3 response element (TRE), and examined the ability of two different forms of in vitro synthesized T3 receptor to bind to the TSH beta gene. The avidin-biotin complex DNA binding assay was used to examine sequence-specific binding of the receptor. [125I]T3-labeled receptor in GH3 cell nuclear extracts bound to a site within the first exon of TSH beta and also to a region immediately upstream of the second transcriptional start site of the gene. In addition, the Hc-erbA beta and r-erbA alpha-1 forms of the T3 receptor each bound to TSH beta and rGH sequences, demonstrating that both alpha- and beta-forms of T3 receptor can bind to TREs exerting either positive or negative transcriptional regulation. Competition experiments showed that both native and in vitro synthesized T3 receptor bound to the first exon of TSH beta with an affinity slightly less than that for the rGH TRE. The two receptor-binding sites of the rTSH beta gene show sequence similarity to adjacent regions of the rGH TRE. These data indicate that negative regulation of rat TSH beta gene transcription may be effected by direct binding of the T3-receptor complex to one or both of the binding sites flanking the second transcriptional start site.

Animals↗
PubMed1988

Isolation and characterization of the gene encoding the alpha-subunit of the rat pituitary glycoprotein hormones.

The gene encoding the common alpha subunit of the rat pituitary glycoprotein hormones was isolated from a rat genomic DNA library. The gene spans approximately 8 kb, and contains four exons and three intervening sequences of 5.4 kb, 1.1 kb and 0.6 kb. Blot hybridization of restriction enzyme digests of rat genomic DNA suggests that the alpha gene is present in a single copy. The coding region and 424 bp of the 5'-flanking region of the gene were sequenced. Primer extension and S1 nuclease analyses revealed a single transcriptional start point downstream from consensus promoter elements. The organization of the rat alpha-subunit gene is similar to that of the human and bovine genes including the sizes and locations of the four exons and three introns. In addition, a region of strong sequence similarity has been identified in the 5'-flanking region of the rat, human and bovine genes. This region includes sequences which are similar to a putative triiodothyronine regulatory element and the previously identified cAMP regulatory region; such sequences may mediate the known effects of these factors on alpha-subunit gene expression.

Animals↗
PubMed1988

Differential carbohydrate processing and secretion of thyrotropin and free alpha subunit. Effects of 1-deoxynojirimycin.

In pulse-chase experiments we compared the kinetics of early carbohydrate processing and subsequent secretion of thyroid-stimulating hormone (TSH) and free alpha subunit under control conditions and after treatment with 1-deoxynojirimycin, an inhibitor of glucosidases I and II. Under control conditions TSH achieved resistance to endo-beta-N-acetylglucosaminidase H (endo H) more rapidly than free alpha (t1/2 0.3 h versus 0.9 h); however, free alpha was secreted more rapidly than TSH (t1/2 2.2 h versus 3.4 h). With 1-deoxynojirimycin, oligosaccharides co-migrating with G3Man9GlcNAc and G2Man9GlcNAc were demonstrated on TSH for the first time, suggesting that previous pulse-chase studies did not disclose these intermediates due to rapid removal of glucose residues from the common G3Man9GlcNAc2 precursor. 1-Deoxynojirimycin delayed the rate of attainment of endo H resistance for both TSH and free alpha, but there was no effect on subunit combination. With 5 mM 1-deoxynojirimycin the amount of secreted free alpha was reduced to 65% of control; secreted TSH was reduced markedly to 17% of control without intracellular accumulation, suggesting increased intracellular degradation. There was no significant toxicity from these doses of 1-deoxynojirimycin on the production or secretion of the two major nonglycosylated pituitary proteins, growth hormone and prolactin, or on at least 10 other secretory proteins. Basal differences in the relative rates of TSH and free alpha processing and secretion as well as differential sensitivity to 1-deoxynojirimycin suggest separate secretory pathways for these two closely related proteins.

1-Deoxynojirimycin↗
PubMed1985

Pretranslational regulation of ectopic hCG alpha production in ChaGo lung cancer cells by sodium butyrate.

Ectopic production of hCG and its free alpha subunit by ChaGo lung cancer cells is stimulated by sodium butyrate. To investigate pretranslational regulation in this system, we examined the response of the hCG alpha and beta subunit mRNAs in ChaGo-K1 cells, a clone that produces free hCG alpha but no hCG or hCG beta in the basal state. When a Northern blot of total RNA from ChaGo cells was hybridized to a [32P]- labeled hCG alpha cDNA probe, a single band was detected that was identical in size (approximately 850 bases) to placental hCG alpha mRNA. RNA from butyrate-stimulated (5 mM, 24 h) ChaGo cells contained 7.7 times as much hCG alpha mRNA as RNA from control ChaGo cells. This increase appeared to be relatively selective since no difference in total polyA-containing mRNA levels was detected between butyrate-treated and control cells by [32P]oligo(dT) hybridization. In addition, no hCG beta mRNA was detected when Northern and dot blots were hybridized to an hCG beta cDNA probe. In a time course experiment, hCG alpha mRNA accumulation in butyrate-treated cells increased significantly by 8 h with a maximum increase of 6.1-fold at 24 h compared to control values. Major differences in immunoactive hCG alpha accumulation were not apparent, however, until after 24 h. These studies show that stimulation of ChaGo hCG alpha production by butyrate can be completely accounted for by pretranslational events and that failure to detect hCG or free hCG beta production by these cells is not due to poorly translatable RNA or post-translational protein degradation. Thus, exclusive ectopic production of only one of the hCG subunits is likely to be due to selective genomic expression.

Butyrates↗
PubMed1985

Differential regulation of hCG alpha and beta subunit mRNAs in JEG-3 choriocarcinoma cells by 8-bromo-cAMP.

The coordinate regulation of human chorionic gonadotropin (hCG) subunit synthesis by JEG-3 choriocarcinoma cells was studied at the pretranslational level. The responses of the hCG alpha and beta mRNAs were measured during stimulation with the potent cAMP analog 8-bromo-cAMP (8-Br-cAMP) using 32P-labeled hCG alpha and beta cDNA probes. The hCG alpha mRNA (850 bases) and beta mRNA (1050 bases) from JEG-3 cells were identical in size to that of their respective mRNAs from placenta, by Northern blot analysis. After 48 h of stimulation with 2 mM 8-Br-cAMP, production of immunoreactive alpha and beta subunits increased 25- and 52-fold, respectively; corresponding levels of the alpha and beta mRNAs increased 36- and 43-fold, respectively, in a dot blot hybridization assay. Total cellular protein, DNA content, and messenger RNA pools were not altered by treatment with 8-Br-cAMP. The temporal coordination of the expression of the hCG alpha- and beta-subunit genes was examined by comparing the time course of stimulation of the respective mRNAs and the production of immunoreactive subunits. The kinetic responses of the alpha and beta mRNAs differed: the increase in hCG alpha mRNA preceded the increase in hCG beta mRNA, while levels of free alpha subunit and intact hCG increased in parallel with the increase in beta mRNA. hCG alpha mRNA levels increased rapidly between 8 and 24 h after the addition of 8-Br-cAMP, and approached a plateau by 48 h. The levels of hCG beta mRNA increased steadily throughout the 8-48 h period. These results demonstrate that the cAMP analog 8-Br-cAMP differentially regulates hCG subunit biosynthesis in JEG-3 cells at a pretranslational level, and that the stimulation by 8-Br-cAMP in this system appears to be relatively selective for hCG subunits.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1984

NLM-CHEMSORT: an algorithm and computer program for sorting chemical names.

An algorithm is described that has been designed to sort medium-size lists of chemical names, including common, generic, trivial, and systematic names and code numbers, into a logical sequence. It successfully sorted more than 99.5% of 3767 names in its first application. Minor revisions then resulted in more than 99.9% success with the same set of names. The algorithm generates an 80-character primary sort key (alphabetic characters only) and a 16-character secondary level sort key (alphanumeric characters). These sort keys are generated de novo from the name as needed and, thus, do not require increased permanent-storage costs. Sorting on the primary sort key (and secondary sort keys when identical primary keys exist) results in logical sequences of chemical names.

Chemical Phenomena↗
PubMed1982

Characterization of the membrane proteins of rat liver lysosomes. Composition, enzyme activities and turnover.

Lysosomes prepared from the livers of untreated rats and from the livers of rats injected with either Triton WR-1339 or dextran yielded membranes that were similar in both polypeptide composition and activities of ATPase and acid 5'-nucleotidase. The administration of Triton WR-1339 (and dextran) resulted in an increase in ATPase activity of liver homogenates that was associated with a parallel increase in the ATPase activity of the lysosomal membrane. On the other hand, plasma membranes appear to be different from lysosomal membranes with respect to polypeptide composition and enzyme activities. The ATPase activity of lysosomal membranes is not affected by ouabain and suramin, inhibitors of the plasma-membrane ATPase. The plasma-membrane alkaline 5'-nucleotidase has little activity at acid pH. Pulse-labelling of lysosomal membranes with [3H]fucose and with [3H]- and [14C]-leucine occurred rapidly, faster than labelling of plasma membranes. The labelling kinetics indicate that lysosomal membranes may be assembled independently of plasma membranes. These data suggest that, in liver, little bulk transport of plasma membrane to lysosomes takes place, and lysosomal-membrane proteins may not be derived from those of plasma membranes.

Animals↗