Inhibitory effect of cortisone acetate on the stimulation of rat liver cytosol l-serine Pyruvate aminotransferase by dibutyryl adenosine 3′,5′-monophosphate

An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine: pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have no effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serine aminotransferase diminishes with the age of animals. Increase in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyrl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed.     

Substrate binding site of microsomal cytochrome P-450 directly faces membrane lipids

Cytochrome P-450, purified from liver microsomes of phenobarbital-treated rabbits, was incorporated into dimyristoylphosphatidylcholine liposomes. The binding of benzphetamine to the liposome-bound cytochrome P-450 was examined by measuring the benzphetamine-induced spectral change at various temperatures. The van't Hoff plot of the apparent spectral dissociation constant showed a distinct break at the temperature of phase transition of the synthetic lipid. On the other hand, no such break was observed for benzphetamine binding to microsomal bound cytochrome P-450. These results suggest that the substrate binding site of cytochrome P-450 is embedded in the apolar interior of phospholipid bilayer membranes.     

Oxidative phosphorylation and proton translocation in membrane vesicles prepared from Escherichia coli

This paper reports physical-chemical properties of proteins L7 and L12 from E. coli 50 S subunits. Evidence is presented that these two proteins behave in their native state as a dimer of molecular weight 24000. From sedimentation velocity and intrinsic viscosity data the actual frictional ratio of the dimer has been obtained revealing an asymmetric particle which can be described as a rod with cell dimensions of L = 130 Å and a diameter of D = 17.0 Å. From small X-ray scattering the radius of gyration (Rg = 37.0 Å), the thickness factor, and the degree of hydration were determined. This indicates that the extended shape of the dimer is due to the asymmetry of the molecule and not to the hydration.     

Splenic lymphocytopoiesis and migration pattern of splenic lymphocytes

The spleens of young pigs were selectively labeled with tritiated thymidine ([³H]-TdR) and the relative and absolute numbers of labeled lymphocytes found 24 hr later in different lymphoid and nonlymphoid organs were determined autoradiographically. It was deduced that about 4.6 × 10⁹ lymphocytes (that is, about 15% of all splenic lymphocytes) are produced by the spleen per day and about 17% of the newly formed lymphocytes leave the spleen within the first day of labeling. Spleen-derived lymphocytes could be found in relatively high numbers in the lymph nodes, blood, gut-associated lymphoid tissues, and, surprisingly, in the bone marrow, whereas the concentration in the thymus was very low. In a second series, pigs were labeled with [³H]TdR and only the spleen was excluded from labeling. The labeling index of splenic small lymphocytes was about 10% 1 day later, indicating a high rate of influx of newly formed lymphocytes into the pig spleen. The spleen of the young pig is an important lymphocytopoietic organ and exports and imports newly formed lymphocytes at high rates.     

A modified preparative gel electrophoresis apparatus with special application to the separation of long polypeptide chains

An apparatus for preparative electrophoresis is described which modifies earlier designs substantially. The apparatus is applicable to both continuous and discontinuous buffer systems. Its efficiency is demonstrated for the separation of the three components of the pyruvate dehydrogenase complex. The modifications are discussed with respect to earlier designs.     

Development and characterization of antisera to 18-hydroxy-corticosterone and 18-hydroxy-11-deoxycorticosterone and radioimmunoassay for serum 18-hydroxycorticosterone

A method for the production of the haptens 18-hydroxy-11-deoxycorticosterone-3-(O-carboxymethyl)-oxime (18-OH-DOC-3-CMO) and 18-hydroxycorticosterone-3-(O-carboxymethyl)-oxime (18-OH-B-3-CMO) is described. The formation of the oximes was studied in kinetic experiments. They were prepared at pH 1.6 in methanol/HC1 using a short reaction time. Antisera were raised in rabbits using serum albumin conjugates. The highly specific antisera were used at a final dilution of 1: 79 000 (18-OH-DOC) and 1: 43 000 (18-OH-B); the affinity constants were 1.2 × 10¹⁰l/mol and 8.1 × 10⁹l/mol, respectively. The radioimmunoassay procedure for 18-OH-B in serum involves purification by paper chromatography. The intra- and interassay precision was 7.3% and 12.3%, respectively. The mean serum 18-OH-B level (± S.D.) for normal male and female ambulatory subjects (n = 40) on a normal sodium diet was 0.802 ± 0.262 nmol/l. After 60 minutes of recumbency, the serum 18-OH-B level was 0.313 ± 0.061 nmol/l (n = 6) for men.