Modification by bovine growth hormone of liver plasma membrane enzymes, phospholipids, and circular dichroism

Liver plasma membrane phospholipid distribution, protein conformation, and 5′-nucleotidase, Mg²⁺-adenosine triphosphatase and (Na⁺ + K⁺)-adenosine triphosphatase specific activities, were shown to depend on pituitary status and treatment with bovine growth hormone.In whole liver homogenates, hypophysectomy produced a decrease in the proportion of phosphatidyl serine, lysophosphatidyl choline, and phosphatidic acid and diphosphatidyl glycerol and an increased proportion of phosphatidyl ethanolamine. The phospholipid distribution in liver plasma membranes was the same for normal and hypophysectomized rats. Plasma membranes obtained from bovine growth hormone-treated hypophysectomized rats had approximately 50%, more phosphatidyl serine than membranes obtained from untreated hypophysectomized or normal rats.Plasma membranes from hypophysectomized rats had 75% of the 5′-nucleotidase, the same level of (Na⁺ + K⁺)-adenosine triphosphatase, and twice the Mg²⁺-adenosine triphosphatase of membranes from normal rats. Twelve hours after administration of bovine growth hormone to hypophysectomized rats, (Na⁺ + K⁺)-adenosine triphosphatase had almost doubled and Mg²⁺-adenosine triphosphatase decreased by 50%. 5′-Nucleotidase remained unchanged. Twenty-four hours after bovine growth hormone administration, both (Na⁺ + K⁺)-adenosine triphosphatase and 5′-nucleotidase had increased. Mg²⁺-adenosine triphosphatase was 23% of the baseline level of untreated hypophysectomized rats. Treatment for 3 days or 5 days increased the 5′-nucleotidase 2-fold.Circular dichroism spectra of liver plasma membranes isolated from hypophysectomized rats consistently showed greater negative ellipticity in the far ultraviolet range (250-190 nm) than those from normal rats or rats treated with bovine growth hormone.     

Effect of bovine growth hormone on rat liver plasma membranes as studied by circular dichroism and fluorescence using the extrinsic probe 7,12-dimethylbenzanthracene

Conformational changes produced by in vitro bovine growth hormone addition to plasma membranes of hypophysectomized rat liver proteins and lipids have been studied by circular dichroism as well as intrinsic and extrinsic fluorescence. 7,12-Dimethylbenzanthracene has been used as a fluorescent probe of changes in membrane structure. The exposure of membranes to bovine growth hormone produced a change in membrane negative ellipticity. Dimethylbenzanthracene at concentrations similar to those employed in fluorescence studies had no effect on the membrane circular dichroism spectrum. Its presence did, however, prevent a response to growth hormone. There was a decrease in peak fluorescence intensity and a peak shift when bovine growth hormone (0.5 · 10^?12 M) was added to liver membranes. The addition of dimethylbenzanthracene (1.6 · 10^?6 M) to membranes resulted in a decrease in the intensity of the protein fluorescence peak at 335 nm and the appearance of two peaks at 430 and 407 nm, assignable to the probe. The addition of bovine growth hormone (0.5 · 10^?12 M) produced a decrease in fluorescence at 335 nm and also in the peaks at 407 and 430 nm. These data are consistent with the conclusion that bovine growth hormone produces a conformational change in rat liver plasma membrane proteins and lipids.     

Effects of growth hormone on ATPase and fluorescence of isolated liver membranes utilizing the fluorescent substrate, 1,N6-etheno-adenosine triphosphate

The influence of bovine growth hormone on Mg²⁺-ATPase (EC 3.6.1.4) in isolated liver plasma membranes of hypophysectomized rats has been investigated in vitro by means of spectrofluorescence measurements in parallel with Mg²⁺-ATPase assays, using 1, N⁶-etheno-ATP as substrate and fluorescence probe.Bovine growth hormone, at concentrations of 10^?14m and above, enhanced significantly Mg²⁺-ATPase activity in the presence of GTP at concentrations from 10^?6m to 10^?10m. Moreover, bovine growth hormone decreased fluorescence intensity of membrane protein at the peak at 330 nm and of 1, N⁶-etheno-ATP at its peak at 395 nm as well. The greatest decrease in fluorescence intensity of 1, N⁶-etheno-ATP was observed in the presence of 5 mm MgCl₂ and 10^?8m GTP, consistent with the stimulating effect of bovine growth hormone on Mg²⁺-ATPase activity. In addition, bovine growth hormone caused a small decrease in fluorescence intensity of 1, N⁶-etheno-ADP, but not the corresponding fluorescent analogs of AMP, cyclic AMP, and adenosine. The decrease in fluorescence intensity of 1, N⁶-etheno-ATP by bovine growth hormone was completely eliminated by addition of ATP, ADP, and cyclic AMP at concentrations five times that of 1, N⁶-etheno-ATP. Neither AMP nor adenosine exerted any effects.Bovine growth hormone also increased the fluorescence polarization of 1, N⁶-etheno-ATP from 0.177 ± 0.006 to 0.212 ± 0.010 at 300 nm under the same conditions employed for the Mg²⁺-ATPase assay.These observations suggest that bovine growth hormone produced changes in tertiary structure of membrane proteins in general and probably Mg²⁺-ATPase in particular with consequent enhanced enzyme activity.     

The fluorescein-mediated interaction of bovine serum albumin with fluorescent derivatives of prolactin and other polypeptides in polarization of fluorescence based assays

During the course of studies relating to the interaction of bovine prolactin with its receptor, it was observed that the fluorescence polarization of prolactin labeled with fluorescein isothiocyanate (fluorescein prolactin) increased from 0.10 to 0.15 upon the addition of bovine serum albumin. Dilution titration measurements show an apparent K_dissociation for the BSA-fluorescein-prolactin complex of 1.1 × 10^?7 M. The stoichiometry of the complex was shown to be approximately 2 mol of fluorescein-prolactin per mole of BSA. The fluorescence emission spectra of the fluorescein moiety in the fluorescein-prolactin is slightly red shifted and increased in intensity in the presence of BSA. The interaction between prolactin and BSA is dependent on the fluorescein attached to the prolactin since [¹²⁵I]prolactin does not form a complex with BSA under identical conditions. The fluorescence polarization of fluorescein-labeled growth hormone and α-lactalbumin also increased in the presence of BSA, suggesting that BSA may interact generally with fluorescein-labeled proteins to form complexes bridged through the fluorescein moiety.     

Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism

Membranes were prepared from fresh, washed human erythrocytes by hemolysis and washing with 5 mm sodium phosphate buffer (pH 7.4). The mean residue ellipticity, [θ], of erythrocyte membrane circular dichroism was altered by prostaglandin E₁ or prostaglandin F_2α at 37 °C when observed from 250 nm to 190 nm. The decrease in negativity of [θ] with 10^?6m prostaglandin E₁ was 12.7% at 222 nm and 17.7% at 208 nm, and with 10^?6m prostaglandin F_2α 22.5% and 34.2%, respectively (P < 0.01). Similar changes in [θ] were observed at lower concentrations of prostaglandins. No strict relationship between amount of change of [θ] and prostaglandin concentrations of 3 × 10^?5m to 3 × 10^?12m was evident. A persistent alteration of [θ] with prostaglandin was observed at 37 °C. Transient change of [θ] occurred at 25 °C with prostaglandin. No change of [θ] was observed at 15 or 20 °C. Buffer or palmitic acid were without effect on membrane [θ]. Phosphatidyl inositol or methyl arachidonate caused an increase in negativity of membrane spectra. The observed alterations of membrane [θ] did not arise from changes in light scattering as the OD₇₀₀–OD₂₀₀ of membranes was not changed by prostaglandin. Effects of prostaglandin were not dependent on light path length. The prostaglandin E₁ antagonist, 7-oxa-13-prostynoic acid, at 10^?7m produced no change of [θ] of membrane spectra and prevented the otherwise demonstrable effects of 10^?10m prostaglandin E₁ on [θ]. The decrease in negativity of [θ] at 222 nm is indicative of a decrease in ellipticity of membrane protein. These studies suggest that prostaglandins may act by inducing a conformational change in membrane protein.     

Growth hormone effects on creatine uptake by muscle in the hypophysectomized rat

Summary Specific radioactive enzyme assays were developed to measure the effect of growth hormone on kidney transamidinase and liver methyltransferase in the hypophysectomized rat. In contrast to minimal changes (20%) in liver methyltransferase, kidney transamidinase was decreased threefold in the hypophysectomized rat. Enzyme activities were equal to normal values in those rats receiving growth hormone for three days. The formation of creatine from radioactive precursors and the uptake of ¹⁴C-creatine in muscle was examined under these conditions. After injection of ¹⁴C-arginine in the hypophysectomized rat, the ¹⁴C-creatine content of muscle was greatly decreased compared to sham operated controls and the ¹⁴C-creatine content was normal after growth hormone administration. After injection of ¹⁴C-guanidoacetate and of ¹⁴C-creatine, the ¹⁴C-creatine content of muscle was decreased in the hypophysectomized rat, but was equal to sham control values in rats receiving growth hormone. These studies indicate that the uptake of newly synthesized creatine by muscle is impaired in the hypophysectomized rat and that growth hormone can have a role in controlling the rate of creatine uptake by muscle in addition to its effect on kidney transamidinase and to other factors involved in creatine metabolism.     

The effects of hypophysectomy and of growth hormone on the uptake of radioactive phosphorus by tissues

Normal and hypophysectomized animals, fed ad lib., both with and without growth hormone treatment, were injected with 4 microcuries of P³²/100 g. body weight, and then autopsied at varying time intervals following the injection.The plasma of hypophysectomized animals possesses a greater P³² activity than normal plasma at all intervals from 0.5 to 24 hr. after P³² injection. Maintenance of hypophysectomized animals with growth hormone results in a plasma P³²-activity level much smaller than that found in the plasma of hypophysectomized controls, yet greater than that found in the plasma of normal animals.The normal liver uptake of P³² shows a maximum between 0.5 and 1 hr. after intraperitoneal injection. Kidney shows a maximum in less than 0.5 hour, and thymus attains a maximum activity level in 2 hr. Hypophysectomy results in an increased liver, kidney, and thymus P³² uptake when compared to the normal. After hypophysectomy the time of maximal P³² activity in liver is shifted to 4 hr. after injection. Growth hormone therapy in the hypophysectomized animal lowers the P³²-uptake levels of kidney and liver toward normal, and brings down the P³² level in thymus to normal.Hypophysectomy with or without growth hormone therapy, results in a muscle P³² accumulation which is less than normal. Growth hormone administration to the normal animal causes an increased P³² accumulation by muscle.The P³² uptake by the tibia of the hypophysectomized rat is less than normal. Maintenance of the hypophysectomized rat with growth hormone prevents the decrease in bone P³² uptake due to hypophysectomy.     

Hypophyseal regulation of hepatic histidase during postnatal development and adulthood: II. Pituitary-estrogen interrelationship

Estrogen, which augments rat liver histidase activity in pre- and postpubertal rats, is ineffective in hypophysectomized animals, in which enzyme activities are already elevated. This failure of estrogen action has been demonstrated in hypophysectomized weanling, as well as adult females, the former of which manifest enzyme activities considerably below maximum possible values. The following agents, which are known to suppress histadase activity under certain conditions, were ineffective in permitting estrogen stimulation of histadase in hypophysectomized rats: glucocorticoid, testosterone, adrenocorticotrophin acting extra-adrenally and via the adrenals, growth, and preparations of whole pituitaries of bovine or female rat origin. The following materials, which do not themselves alter enzymic activity, were likewise incapable of permitting estrogenic enhancement of histadase activity in these animals: follicle-stimulating hormone and luteinizing hormone acting extra-gonadally, thyrotrophic hormone, and bovine posterior pituitary preparations.     

Enhancing Diamond Fluorescence via Optimized Nanorod Dimer Configurations

Light extraction from silicon (SiV) and nitrogen (NV) vacancy diamond color centers coupled to plasmonic silver and gold nanorod dimers was numerically improved. Numerical optimization of the coupled dipolar emitter—plasmonic nanorod dimer configurations was realized to attain the highest possible fluorescence enhancement by simultaneously improving the color centers excitation and emission through antenna resonances. Conditional optimization was performed by setting a criterion regarding the minimum quantum efficiency of the coupled system (cQE) to minimize losses. By comparing restricted symmetric and allowed asymmetric dimers, the advantages of larger degrees of freedom achievable in asymmetric configurations was proven. The highest 2.59?×?10⁸ fluorescence enhancement was achieved with 46.08% cQE via NV color center coupled to an asymmetric silver dimer. This is 3.17-times larger than the 8.19?×?10⁷ enhancement in corresponding symmetric silver dimer configuration, which has larger 68.52% cQE. Among coupled SiV color centers the highest 1.04?×?10⁸ fluorescence enhancement was achieved via asymmetric silver dimer with 37.83% cQE. This is 1.06-times larger than the 9.83?×?10⁷ enhancement in corresponding symmetric silver dimer configuration, which has larger 57.46% cQE. Among gold nanorod coupled configurations the highest fluorescence enhancement of 4.75?×?10⁴ was shown for SiV color center coupled to an asymmetric dimer with 21.8% cQE. The attained enhancement is 8.48- (92.42-) times larger than the 5.6?×?10³ (5.14?×?10²) fluorescence enhancement achievable via symmetric (asymmetric) gold nanorod dimer coupled to SiV (NV) color center, which is accompanied by 16.01% (7.66%) cQE.     

A fluorescent compound in oat root plasma membrane

Homogenates of 7-day-old oat (Avena sativa L. cv. Brighton) roots were highly fluorescent (excitation and emission maxima around 360 and 440 nm, respectively). Less than ¹/₁₀ as much fluorescence per g fresh weight was found in oat shoots or in wheat (Triticum aestivum L. cv. Drabant) roots or shoots. Most of the fluorescence of oat roots was found in the soluble fraction (150 000g supernatant). However, some could be detected in the plasma membrane fraction (excitation and emission maxima 365 and 417 nm, respectively), which contained a 3-fold higher fluorescence per mg protein than the homogenate. Growth of oat or wheat in a medium containing, 10-^?5M scopoletin (6-methoxy-7-hy-droxy coumarin), a fluorescent compound previously reported to be present in both wheat and oat roots, caused the disappearance of scopoletin from the medium (proportional to the amount of roots) and the appearance of increased fluorescence in the root homogenates but not in the shoot homogenates. In both oat and wheat roots ail of the extra fluorescence was recovered in the soluble fraction and at least in wheat it consisted of unconverted scopoletin. The concentration of scopoletin in wheat roots grown in 10-^?5M scopoletin was around 50 nmol (g fresh weight)^?1, or about five times the concentration in the growth medium. Scopoletin in the growth medium (10-^?5M) or in the assays (up to 10-^?4M) did not affect Mg²⁺-, Mg²⁺+K⁺- or Ca²⁺-ATPase activities in wheat or oat roots. The fluorescence properties of the oat plasma membrane were different from those of authentic scopoletin. Either the surroundings modify the fluorescence of membrane-associated scopoletin or the endogenous fluorescent compound is not scopoletin but a glycoside-derivative of scopoletin or some completely unrelated compound.     

Regulation of fatty acid and carbohydrate metabolism by insulin, growth hormone and tri-iodothyronine in hepatocyte cultures from normal and hypophysectomized rats.

The interactions of insulin, growth hormone (somatotropin) and tri-iodothyronine (T3) in the long-term (24 h) regulation of fatty acid and carbohydrate metabolism were studied in hepatocyte primary cultures isolated from normal or hypophysectomized Sprague-Dawley rats. Hepatocytes from hypophysectomized rats had similar rates of palmitate metabolism, but lower rates of ketogenesis, than hepatocytes from normal rats. They also had a lower endogenous triacylglycerol content and lower activities of NADP-linked dehydrogenases than did cells from normal rats. The inhibitions of ketogenesis and gluconeogenesis by insulin were more marked in hepatocytes from hypophysectomized than from normal rats. Insulin caused a 7-10-fold increase in cellular glycogen in hepatocytes from hypophysectomized rats, compared with a 2-3-fold increase in cells from normal rats, and it increased cellular triacylglycerol by 65% in cells from hypophysectomized rats, compared with 11% in cells from normal rats. In hepatocytes from hypophysectomized rats, growth hormone and T3 increased ketogenesis both separately and in combination (12% and 23% respectively; P less than 0.05), whereas in hepatocytes from normal rats only the combination of growth hormone and T3 caused a significant increase in ketogenesis. In cells from hypophysectomized rats, T3 and growth hormone had different effects on carbohydrate metabolism: T3, but not growth hormone, potentiated the anti-gluconeogenic and glycogenic effects of insulin. It is concluded that hypophysectomy increases the responsiveness of hepatocytes to insulin, growth hormone and T3, and that growth hormone and T3 regulate fatty acid and carbohydrate metabolism by different mechanisms.     

Activation of adenylate cyclase in renal medulla by bovine growth hormone: An artifact attributable to vasopressin

The effect of bovine growth hormone on adenylate cyclase activity was studied in bovine and rat renal medulla. Highly purified growth hormone (lot B1003A) increased adenylate cyclase activity in plasma membranes from bovine renal medulla from 132 ± 6 pmol cyclic AMP formed/mg protein per 10 min to 364 ± 10 pmol cyclic AMP formed/mg protein per 10 min. Similar results were seen with homogenates of rat renal medulla. The minimum effective concentration of bovine growth hormone required to activate adenylate cyclase was 0.5 μg/ml and maximum activation was detected at 500 μg/ml. The amount of vasopressin determined by radioimmunoassay to contaminate the growth hormone caused an increase in adenylate cyclase activity comparable to that of the corresponding concentration of growth hormone that was tested. Dialysis of growth hormone and vasopressin resulted in parallel reductions in the effect of each hormone on adenylate cyclase activity. Similarly, both growth hormone and vasopressin produced increases in short circuit current in isolated toad bladders but these effects were not detectable after dialysis of the hormones. In contrast, the effect of growth hormone on the uptake of ³⁵SO₄²⁻ by cartilage from hypophysectomized rats was not decreased after dialysis. These results indicate that available preparations of growth hormone are contaminated by small but physiologically significant amounts of vasopressin and that the activation of adenylate cyclase activity in renal medulla in response to growth hormone can be explained by this contamination rather than by an effect of growth hormone per se.     

Influence of growth hormone on bone marrow adipogenesis in hypophysectomized rats

The hypophysectomized rat has been used as a model to study the effects of growth hormone deficiency on bone. Here, we have investigated the influence of growth hormone administration to hypophysectomized rats (HX) for 6 wk on accumulation of triglycerides in bone marrow and on the differentiation of primary marrow stromal cells into adipocytes under in vitro conditions. We found that hypophysectomy significantly increased triglyceride concentration in bone marrow, which was attenuated by growth hormone administration. Primary bone marrow stromal cells derived from HX rats also had more adipocytes at confluence compared with growth hormone-treated hypophysectomized (GH) rats. When stimulated with 3-isobutyl-1-methylxanthine plus dexamethasone (IBMX-Dex), preadipocyte colony counts increased more significantly in GH rats. Markers of adipocyte differentiation were higher in HX than in control or GH rats at confluence. However, after stimulation with IBMX-Dex, increased expression of markers was seen in GH compared with HX rats. In conclusion, growth hormone administration to hypophysectomized rats attenuated triglyceride accumulation in bone marrow and inhibited the differentiation of stromal cells into adipocytes in vitro.     

Nerve growth factor induced turnover of phosphatidylinositol in rat superior cervical ganglia

The addition of nerve growth factor to organ cultures of superior cervical ganglia from immature rats specifically stimulated the incorporation of 32P-orthophosphate into phosphatidylinositol fraction. Equimolar concentrations of other hormones such as insulin, glucagon, thyroxine and growth hormone did not cause any stimulation of the incorporation of 14C-myoinositol into phosphatidylinositol. The stimulation of phosphatidylinositol turnover was observed over a concentration of nerve growth factor ranging from 10^?10M to 10^?7M. Nerve growth factor specific “inositide effect” was found to be sensitive to nerve growth factor antibody, 2,4-dinitrophenol, a high concentration of bovine growth hormones but not to Actinomycin D. The physiological significance of this finding in relation to nerve growth factor action in this target tissue is discussed.     

Luminescence of bacteriorhodopsin from Halobacterium halobium and its connection with the photochemical conversions of the chromophore

Red luminescence of purple membranes from Halobacterium halobium cells in suspension, dry film or freeze-dried preparations was studied and its emission, excitation and polarization spectra are reported. The emission spectra have three bands at 665–670, 720–730 and at 780–790 nm. The position (maximum at 580 nm) and shape of the excitation spectra are close to those of the absorption spectra. The spectra depend on experimental conditions, in particular on pH of the medium. Acidification increases the long wavelength part of the emission spectra and shifts the main excitation maximum 50–60 nm to the longer wavelength side. Low-temperature light-induced changes of the absorption, emission and excitation spectra are presented. Several absorbing and emitting species of bacteriorhodopsin are responsible for the observed spectral changes. The bacteriorhodopsin photoconversion rate constant was estimated to be about 1 · 10¹¹ s^?1 at ? 196°C from the quantum yields of the luminescence (1 · 10^?3) and photoreaction (1 · 10^?1). The temperature dependence of the luminescence quantum yield points to the existence of two or three quenching processes with different activation energies. High degree of luminescence polarization (about 45–47%) throughout the absorption and fluorescence spectra and its temperature independence show that there is no energy transfer between bacteriorhodopsin molecules and no chromophore rotation during the excitation lifetime. In carotenoid-containing membranes, energy migration from the bulk of carotenoids to bacteriorhodopsin was not found either. Bacteriorhodopsin phosphorescence was not observed in the 500–1100 nm region and the emission is believed to be fluorescence by nature.     

Additive effects of thyroid hormone,growth hormone and testosterone on deoxyribonucleic acid-dependent ribonucleic acid polymerase in rat-liver nuclei

1. The stimulations of DNA-dependent RNA polymerase in isolated rat-liver nuclei by thyroid hormone, human growth hormone and testosterone are compared. 2. Single or multiple administrations of growth-promoting doses of tri-iodo-l-thyronine, human growth hormone and testosterone stimulate the Mg²⁺-activated RNA-polymerase reaction in nuclei from thyroidectomized, hypophysectomized and castrated rats respectively. The magnitude of stimulation was proportional to the degree of enhancement of liver growth by each hormone. After a single injection, the latent period preceding the stimulation was 1, 2 and 10hr. for growth hormone, testosterone and tri-iodothyronine respectively. The time-course of stimulation of enzyme activity and the synthesis of rapidly labelled nuclear RNA in vivo were also different for each hormone. 3. Growth hormone administration failed to stimulate the Mn²⁺/ammonium sulphate-activated RNA-polymerase reaction. Thyroid hormone and testosterone, however, stimulated it but the effect was less pronounced and occurred several hours later than that observed for the Mg²⁺-activated RNA-polymerase reaction. 4. In combination experiments, hypophysectomized or the thyroidectomized rats were given growth hormone or tri-iodothyronine in a single or repeated doses at levels that produced the maximum stimulation of Mg²⁺-activated RNA-polymerase activity. Taking into account the different latent period for each hormone, a single administration of the second hormone caused an additional stimulation of the enzyme activity. Similar additive effects were observed in thyroidectomized–castrated rats after treatment with tri-iodothyronine and testosterone. The magnitude of the additional stimulation caused by the administration of the second hormone was compatible with the capacity of that hormone to promote liver growth in rats deprived of it. 5. It is concluded that, although these hormones have some similar effects, the regulation of nuclear RNA synthesis may be mediated via different routes for each hormone.     

Stimulation of ornithine decarboxylase activity in rat tissues by growth hormone and by serum growth factor from rats infested with spargana of Spirometra mansonoides

Ornithine decarboxylase activity was studied in heart, kidney, liver, thymus, lung, spleen, skeletal muscle and fat of hypophysectomized rats after growth hormone treatment. A marked increase in enzyme activity was observed in kidney and liver, and a significant increase in heart and thymus at 4 h after injection of growth hormone. The kidney was the most responsive organ with an increase in activity of about 100 fold. The enzyme activity in kidney responded to a dose of 10 μg of growth hormone. Daily injection for 12 days raised activity only in the heart. Infestation for 6–13 days with spargana of Spirometra mansonoides, which also causes growth of hypophysectomized rats, increased enzyme activity in the heart and thymus. Intravenous injection of serum of hypophysectomized rats infested with spargana of Spirometra mansonoides caused a significant increase in the enzyme activity in liver and kidney after 4 h. Growth hormone and the serum growth factor of sparganosis seem to share the characteristic of causing an early increase in ornithine decarboxylase activity in rat tissues. The marked response in kidney and liver raises the possibility that these organs are the primary targets of both substances.     

Stimulation of cartilage amino acid uptake by growth hormone-dependent factors in serum: Mediation by adenosine 3′:5′-monophosphate

The effects of growth hormone-dependent serum factors on amino acid transport and on cartilage cyclic AMP levels in embryonic chicken cartilage were studied in vitro. Cartilages incubated in medium containing rat serum showed a significantly greater uptake of α-amino [1-¹⁴C] isobutyrate or [1-¹⁴C] cycloeeucine than control cartilages incubated in medium alone. Normal rat serum (5%) added to the incubation medium also caused an increase in cartilage cyclic AMP content (from as little as 23% to as much as 109%). The factors in serum which increase cartilage cyclic AMP and amino acid uptake are growth hormone dependent, since neither growth hormone itself nor serum from hypophysectomized rats affects either parameter. Growth hormone treatment of hypophysectomized rats restores these serum factors. Studies comparing the ability of sera with varying amounts of growth hormone-dependent factors to stimulate α-aminoisobutyrate transport and to increase cartilage cyclic AMP show a striking linear correlation between the two effects (r = 0.977). Theophylline and prostaglandin E₁, which raise cartilage cyclic AMP also increase α-aminoisobutyrate transport. Exogenous cyclic AMP, N⁶-monobutyrll cyclic AMP and N⁶, O²′-dibutyryl cyclic AMP increase cartilage α-aminoisobutyrate transport. The data are compatible with the thesis that growth hormone-dependent serum factors increase cartilage amino acid transport by elevating cartilage cyclic AMP.     

Lutein-chlorophyll-a energy transfer in detergent micelles

Absorption, fluorescence and fluorescence excitation spectra were determined for equimolar mixed micellar detergent solutions of lutein and chlorophyll-a in the concentration range from 9·10^?6 to 1.8·10^?4 M, with detergent (triton-X100) concentrations from 3·-10^?4 to 7·10^?3 M. In the range of detergent concentrations studied the pigments incorporated into the detergent micelles attained a high local concentration (0.1 to 0.01 M), reminiscent of pigment concentration within the chloroplast. A lutein → chlorophyll-a energy transfer with an efficiency of about 15% was found in these systems. In dilute (9·10^?6 M) pigment solution with concentrated (7·10^?3 M) detergent practically no transfer is observed. The extent of aggregation and the efficiency of transfer depend on the composition of the system. The aggregation of chlorophyll-a is partly inhibited by lutein molecules. It is shown that the energy transfer efficiency as function of distance follows anr ^?3 relationship,R ₀ being 22 å.