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Studies on the relationship between the degradative rates of proteins in vivo and their isoelectric points.

ABSTRACT: Acidic proteins tend to be degraded more rapidly than neutral or basic proteins in rat liver, skeletal muscle, kidney and brain and in mouse liver and skeletal muscle. We now report a similar relationship among soluble proteins from rat lung, heart and testes, and from human fibroblasts and mouse-embryo cells grown in culture. These findings indicate that the correlation between protein net charge and degradative rate is a general characteristic of intracellular protein degradation in mammals. This relationship between isoelectric point and half-life appears to be distinct from the previously reported correlation between subunit molecular weight and protein half-lives. The more rapid degradation of acidic proteins does not result from their being of larger molecular weight than neutral or basic proteins. Furthermore, proteins within specific isoelectric point ranges still exhibit a relationship between subunit size and half-life. Finally, a group of membrane or organelle-associated proteins that are insoluble in phosphate-buffered saline and water but soluble in 1% Triton X-100 exhibit a correlation between size and half-life, but not between net charge and half-life. The biochemical reasons for the relationship between protein isoelectric point and half-life are unclear, although several possible explanations are presented. It is not due to a greater sensitivity of acidic proteins to proteolytic attack since experiments with a variety of endoproteinases, including trypsin, chymotrypsin, Pronase, papain, chymopapain, Staphylococcus aureus V8 proteinase, pepsin and lysosomal cathepsins from rat liver, have failed to demonstrate more rapid digestion of acidic proteins.

SUBMITTER: Dice JF

PROVIDER: S-EPMC1186516 | biostudies-other | 1979 Feb

REPOSITORIES: biostudies-other

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Project description:BackgroundThe distribution of isoelectric point (pI) of proteins in a proteome is universal for all organisms. It is bimodal dividing the proteome into two sets of acidic and basic proteins. Different species however have different abundance of acidic and basic proteins that may be correlated with taxonomy, subcellular localization, ecological niche of organisms and proteome size.ResultsWe have analysed 1784 proteomes encoded by chromosomes of Archaea, Bacteria, Eukaryota, and also mitochondria, plastids, prokaryotic plasmids, phages and viruses. We have found significant correlation in more than 95% of proteomes between the protein length and pI in proteomes--positive for acidic proteins and negative for the basic ones. Plastids, viruses and plasmids encode more basic proteomes while chromosomes of Archaea, Bacteria, Eukaryota, mitochondria and phages more acidic ones. Mitochondrial proteomes of Viridiplantae, Protista and Fungi are more basic than Metazoa. It results from the presence of basic proteins in the former proteomes and their absence from the latter ones and is related with reduction of metazoan genomes. Significant correlation was found between the pI bias of proteomes encoded by prokaryotic chromosomes and proteomes encoded by plasmids but there is no correlation between eukaryotic nuclear-coded proteomes and proteomes encoded by organelles. Detailed analyses of prokaryotic proteomes showed significant relationships between pI distribution and habitat, relation to the host cell and salinity of the environment, but no significant correlation with oxygen and temperature requirements. The salinity is positively correlated with acidicity of proteomes. Host-associated organisms and especially intracellular species have more basic proteomes than free-living ones. The higher rate of mutations accumulation in the intracellular parasites and endosymbionts is responsible for the basicity of their tiny proteomes that explains the observed positive correlation between the decrease of genome size and the increase of basicity of proteomes. The results indicate that even conserved proteins subjected to strong selectional constraints follow the global trend in the pI distribution.ConclusionThe distribution of pI of proteins in proteomes shows clear relationships with length of proteins, subcellular localization, taxonomy and ecology of organisms. The distribution is also strongly affected by mutational pressure especially in intracellular organisms.

Project description:BACKGROUND:Globalization of clinical trials fosters inclusion of higher and lower income countries, but the influence of enrolling country income level on heart failure trial performance is unclear. This study sought to evaluate associations between enrolling country income level, acute heart failure patient profile, protocol completion, and trial end points. METHODS AND RESULTS:The ASCEND-HF (Acute Study of Clinical Effectiveness of Nesiritide in Decompensated Heart Failure) trial included 7141 patients with acute heart failure from 30 countries. Country income data in gross national income per capita in current US dollars from the year 2007 (ie, the year trial enrollment began) were abstracted from the World Bank. Patients were grouped by enrolling country income level (ie, high [>$11 455], upper middle [$3706-$11 455], lower middle [$936-$3705], and low [<$936]). Income data were available for 29 (97%) countries (N=7064). There were 3996 (57%), 1518 (21%), and 1550 (22%) patients from high-income, upper-middle-income, and lower-middle-income countries, respectively. There were no patients from low-income countries. Patients from lower-middle-income countries tended to be younger with fewer comorbidities and lower utilization of guideline-directed therapies. Rates of adverse events (13.8%) and protocol noncompletion (4.9%) during 180-day follow-up were highest among high-income countries (all P <0.01). After adjustment for race, geographic region, and clinical characteristics, compared with lower-middle-income countries, enrollment from higher income countries was associated with increased 30-day mortality or rehospitalization (high income: odds ratio, 1.70; 95% CI, 1.02-2.85; upper-middle-income: odds ratio, 2.16; 95% CI, 1.23-3.81), driven by higher rates of rehospitalization. Mortality was similar at 30 and 180 days. The association between higher country income and the 30-day composite end point was similar across geographic regions, with exception of Latin America ( P for interaction, 0.03). CONCLUSIONS:In this global acute heart failure trial, patients from higher income countries had lower rates of protocol completion, higher rates of adverse events, and similar mortality rates. After adjustment for race, geographic region, and clinical factors, enrollment from a higher income country was associated with worse clinical outcomes, driven by higher rates of rehospitalization. Variation in enrolling country income level may influence study end points and trial performance independent of geographic region. CLINICAL TRIAL REGISTRATION:URL: https://www.clinicaltrials.gov . Unique identifier: NCT00475852.

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Studies on the relationship between the degradative rates of proteins in vivo and their isoelectric points.

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