Artemia hemoglobins: Increase in net synthesis of the β-polypeptide (relative to the α-polypeptide) in hypoxia

Previous studies have shown that in the brine shrimp there are three dimeric hemoglobins with polypeptide composition α₂, αβ, β₂. Concentrations of the α- and β-polypeptides increase in hypoxia. We now report a two-dimensional electrophoretic method for assay of radiolabelled polypeptidesin each hemoglobin. Net synthesis (synthesis minus degradation) of the β-chain, relative to that of the α-chain, increases more than 3-fold (in male and female adults) within 3 days following a downshift in oxygen concentration from 0.2 to 0.1 mM in the culture medium. 3 days after downshift (2 days after in vivo incorporation of radiolabelled leucine), the β-homodimer contained 10–20% of the radiolabel in the three hemoglobins although β₂ was usually not detectable in the protein stain of an overloaded gel. The amount of radioactive leucine incorporated per unit amount of protein was more than 300-times greater in the β₂ homodimer than in the β-subunit of the heterodimer, suggesting that β₂ does not dissociate rapidly during electrophoresis on the first dimension non-denaturing gel. This evidence for stable association of the two β-monomers and the 5–8 heme-binding domains within each monomer (in vivo and during electrophoresis on non-denaturing gels) allows us to exclude one of two alternative interpretations of genetic data published previously. We present an independent line of evidence for the dimer model of the native hemoglobins (which states that each polypeptide has many heme-binding domains).     

STATISTICAL EVALUATION OF SIEVE CONSTANTS IN ULTRAFILTRATION

The partial retention of the disperse phase in the ultrafiltration of a monodisperse system through an isoporous filter is interpreted on a statistical basis, and a simple expression for the sieve constant is evaluated in terms of the calibrated membrane porosity and the particle size. Curves calculated from this expression are in reasonable agreement with experimental data for the ultrafiltration of serum albumin, hemocyanin (Helix), and foot-and-mouth disease virus.     

Blood lactate accumulation in intermittent supramaximal exercise

Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172 +/- 5% VO2max for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and VO2 was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration [( LA]b) occurred, whereas its rate of accumulation (delta[LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. VO2 values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in delta[LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multi-compartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session.(ABSTRACT TRUNCATED AT 250 WORDS)     

Proteolysis of rat liver plasma membranes cancels the guanine nucleotide sensitivity of agonist binding to the alpha-adrenoceptor

Incubation of rat liver plasma membranes with a variety of proteinases causes a time and dose-dependent 2- to 3-fold increase in (?)-[³H]norepinephrine binding to the alpha-adrenergic receptor. Scatchard analysis of binding data shows that both the number of sites and the affinity of the ligand are increased. Following proteolysis, the association and dissociation rates of binding of the hormone are increased. Guanine nucleotides decrease the affinity of the agonist for the alpha-adrenoceptor in untreated membranes, but not in alpha-chymotrypsin-treated membranes. Thus, limited proteolysis of liver membranes results in drastic modifications, not only on the binding characteristics of catecholamines to the alpha-adrenoceptor, but also on its regulation by guanine nucleotides.     

Human intestinal tissue-resident memory T cells comprise transcriptionally and functionally distinct subsets

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