Association of LHIα(B870) Polypeptide with Phospholipids During Insertion in the Photosynthetic Membrane of an LHII− Mutant of Rhodobacter capsulatus

Membranes from in vivo labeled cells of Rhodobacter capsulatus U43[pTX35] grown photosynthetically carried 60% of the [³²P]-Pi in the “heavy” fraction (HM) after sucrose gradient sedimentation. Metal-chelating chromatography of either “heavy” or “light” (LM) membrane fractions rendered similar Bchl-protein complex profiles after octyl-glucoside treatment, including most of the radioactivity in the same corresponding elution fraction (F II). Similar labeling distribution of pigment-protein complexes was obtained for membranes of dark-grown cells induced by lowering oxygen tension. Fractions derived from HM showed highly labeled LHIα, whereas the same complex from LM was essentially [³²P]-Pi-free, as revealed by SDS-PAGE followed by autoradiography. Phospholipid analysis showed a similar pattern for membranes isolated from cells photosynthetically or semiaerobically grown, being the most abundant: phosphatidylglycerol, phosphatidylethanolamine, cardiolipin, and phosphatidylcholine. Part of the phospholipids from HM comigrated with LHIα during SDS-PAGE and dissociated from the complexes only after solvent extraction and hydrophobic chromatography. However, a small amount remained always attached to LHIα, indicating an unusual strong interaction. These results suggest the existence of two operationally defined membrane regions carrying LHIα complexes differing in phosphorylation status and protein-phospholipid interaction. Received: 10 August 1996 / Accepted: 10 September 1996     

Carbon Sequestration of Caesalpinia platyloba S. Watt (Leguminosae) (Lott 1985) in the Tropical Deciduous Forest

Caesalpinia platyloba was evaluated as an alternative for the retention of atmospheric carbon and as a feasible and viable economic activity in terms of income for tropical deciduous forest (TDF) peasants in the carbon markets. A total of 110 trees of C. platyloba from plantations and a TDF in the Northwest of Mexico were sampled. Growth (increase in height, diameter, and volume curves) was adjusted to assess their growth. Growth of individuals (height, diameter at breast height [DBH], age, and tree crown cover) was recorded. The Schumacher model (H = β₀e^β₁•E-1), by means of the guided curve method, was used to adjust growth models. Information analysis was made through the non-linear procedure with the multivariate secant or false position (DUD) method using the SAS software. Growth and increase models revealed acceptable adjustments (pseudo R²>0.8). C. platyloba reaches >8m of height with 12cm in diameter and 550cm³ of volume, presenting the highest increase at 11 years considered as basal age. Highest significant density of wood was in good quality sites (0.80g•cm^-3), with a carbon content (average of 99.15tC•ha^-1) at the highest density of 2500 trees•ha^-1 (without thinning). Average incomes of US$483.33tC•ha^-1 are expected. The profitability values (NPW = US$81,646.65, IRR = 472%, and B/C = 0.82) for C. platyloba make its cultivation a viable and profitable activity, considering a management scheme of the income derived from wood selling and from carbon credits.     

Sex-dependent effect of melatonin on the secretory activity of rat and hamster adrenal gland in vitro

Adrenal quarters from adult male or female hamsters were incubated in the presence of melatonin (10(-7) or 10(-4)M), and cortisol concentration in the incubation medium was assayed by RIA. Melatonin did not change cortisol output by adrenals obtained from the male hamsters, while a slight stimulatory effect was observed in female glands, the lower concentration of melatonin being more effective than the higher one. At both concentrations tested, melatonin notably stimulated corticosterone output by isolated rat adrenocortical cells derived from the males, and lowered corticosterone secretion by the cells obtained from the female glands only at a concentration of 10(-7) M. The lower concentration of melatonin increased ACTH (0.1 mU.ml-1)-stimulated corticosterone output by the cells of male and female rat adrenals. The pineal hormone was ineffective at a concentration of 10(-4) M, as well as in the presence of a higher dose of ACTH (1.0 mU.ml-1). These findings indicate a distinct sex-dependent effect of melatonin on in vitro cortisol and corticosterone production, and demonstrate that the modulatory effect of melatonin of the secretion of steroid hormones is more effective at lower concentrations.     

Purification and properties of AMP-deaminase from human uterine smooth muscle. Regulation by adenylate energy charge and activated fatty acids

At pH 7.0 and physiological concentrations of the main regulatory ligands (ATP, ADP, orthophosphate), human uterine muscle AMP-deaminase follows a hyperbolic type of saturation kinetics with S0.5 parameter value about 2 mM. The enzyme is regulated by adenylate energy charge (AEC) variations, being the most active at the AEC value 0.5-0.6 or 0.5-0.7, depending on the size of the total adenine nucleotide pool. Long-chain acyl-CoA strongly inhibit activity of the enzyme, influencing mainly the maximum velocity of the reaction.     

Depletion of taurine in the adult rat retina

Taurine is the major free amino acid of the vertebrate retina. Treatment of rats with guanidinoethyl sulfonate (GES), a taurine analogue which competes with taurine for transport sites, leads to depletion of 60% of retinal taurine with little effect on other free amino acids. Supplementation of the diet with 0.3% taurine gives partial protection against depletion, confirming that taurine-GES competition underlies part of the effects. The magnitude of the depletion suggests the importance of taurine transport across the blood-retinal barrier for the maintenance of retinal taurine levels.     

Properties of carboxypeptidase A-treated chicken gizzard tropomyosin

Chicken gizzard tropomyosin was digested with carboxypeptidase A at the weight ratios of enzyme to substrate 1:200 and 1:50. Removal of about 16 C-terminal amino acid residues per tropomyosin molecule, at lower enzyme concentration, caused reversion of the effect on skeletal actomyosin ATPase activity from activating to inhibiting without an influence on polymerizability and actin-binding ability. Removal of about 26 C-terminal amino acid residues per molecule, at higher enzyme concentration, resulted in loss of polymerizability and actin binding ability. Digestion of gizzard tropomyosin with carboxypeptidase A has no dramatic effect on its binding to troponin T. The results show that not only the existence of head-to-tail overlapping regions but also their length is important for the functional properties of chicken gizzard tropomyosin.