Structure of a porcine relaxin inactive on the mouse pubic ligament

In addition to B31 (CM-a) and B28 (CM-B) relaxins, acid-acetone extracts of ovaries of pregnant sows contain a third major relaxin species (relaxin C). The major components of relaxin C possess about half the activity of CM-a or CM-B in the guinea pig palpation assay, but are completely inactive in the mouse pubic ligament assay. Its uterotrophic and protein anabolic effects in ovariectomized, estrogen-primed mice, however, are comparable to those of CM-B. Sequence analysis indicates that the two major components of relaxin C, like the other porcine relaxins, consist of two polypeptide chains linked by disulfide bonds. The shorter (A) chains are identical to the A chains of the other porcine relaxins, except for the absence of the N-terminal arginine residue. The B chains display microheterogeneity; the B sequences of the two predominant species are the same as those of the other porcine relaxins through B25, but terminate at valine residue B25 or serine residue B26, respectively.     

Somatic instability of carotenoid biosynthesis in the tomato ghost mutant and its effect on plastid development

The tomato (Lycopersicon esculentum (L.) Mill.) ghost plant is a mutant of the San Marzano cultivar affected in carotenoid biosynthesis. ghost plants exhibit a variable pattern of pigment biosynthesis during development. Cotyledons are green but true leaves are white. Green sectors, which appear to be clonal in origin, are frequently observed in the white tissue. Because of the lack of photosynthesis ghost plants have a very low viability in soil. We have developed a strategy for propagating ghost plants that employs organ culture to generate variegated green-white plants which, supported by the photosynthetic green areas, develop in soil to almost wild-type size. These plants were used to analyze the pigment content of the different tissues observed during development and plastid ultrastructure. Cotyledons and green leaves contain both colored carotenoids and chlorophyll but only the colorless carotenoid phytoene accumulates in white leaves. the plastids in the white tissue of ghost leaves lack internal membrane structures but normal chloroplasts can be observed in the green areas. The chromoplasts of white fruits are also impaired in their ability to form thylakoid membranes.     

Stimulation of Ca efflux from fura-2-loaded platelets activated by thrombin or phorbol myristate acetate

We investigated the restoration of [Ca²⁺]_i in fura-2-loaded human platelets following discharge of internal Ca²⁺ stores in the absence of external Ca²⁺. After stimulation by thrombin [Ca²⁺]_i returned from a peak level of 0.6 μM to resting levels within 4 min. When ionomycin discharged the internal stores the recovery was slower with [Ca²⁺]_i still elevated at around 0.5 μM after 5 min. Thrombin added shortly after ionomycin could accelerate the recovery of [Ca²⁺]_i and restore resting levels within 5 min, an effect that was mimicked by phorbol-12-myristate-13-acetate (PMA). Since the continued presence of ionomycin precluded reuptake into the internal stores we conclude that thrombin and PMA stimulate Ca²⁺ efflux, perhaps via protein kinase C actions on a plasma membrane Ca²⁺ pump.     

Polysaccharide production in liquid cell suspension cultures of Phleum pratense L.

The production of carbohydrates by cell suspension cultures of Phleum pratense (timothy grass) is described. Extracellular polysaccharides similar in monosaccharide composition to native cell wall polymers were accumulated, together with polymers of fructose (fructans). The fructans had similar properties to the intracellular reserve polymers found in intact plants, and were found in both cells and media of young, slow-growing cultures.Production of extracellular polysaccharides differed in cultures grown on sucrose or equimolar glucose/fructose as carbon source. These differences were observed only when autoclaved media were used, and were not related to changes in either pH or osmolarity. Autoclaving medium containing radioactive glucose and fructose produced a novel, unidentified labelled compound which was absent in medium containing labelled sucrose.     

Alterations in plasma volume, electrolytes and protein during incremental exercise at different pedal speeds

We investigated the effects of pedal speed on changes in plasma volume, electrolytes and protein during incremental exercise. Ten adult males participated in two, 30 minute incremental cycle ergometer exercise tests at room temperature (22° C, rh=56%). Exercise load was increased from 20 to 70% of peak . Five minutes were spent at each of six stages which were equally spaced in exercise intensity. Subjects pedaled at 50 (50 RPM) and 90 (90 RPM) rev · min^–1. Venous blood samples were drawn prior to exercise and during the last minute of each stage. Relative plasma volume changes showed a progressive hemoconcentration during the exercise. There were no significant differences due to pedal speed as plasma volume loss averaged –7.3% during exercise. [Na+], [Cl–], and [K+] increased significantly during exercise but were not influenced by pedal speed. Changes in plasma protein and albumin concentrations indicated that there was a loss of globulin from the vascular volume in both conditions and an addition of albumin to the plasma in 50 RPM. The difference in plasma albumin dynamics was possibly related to an effect of pedal speed on movement of fluid in the lymphatic vessels of the legs.This work was supported in part by Grants from the Theresa Monaco Endowment of the University of Houston College of Education and Nautilus Sports/Medical Industries