The modifying effect of gibberellic acid and kinetin on the growth abnormalities induced by 2,4-D in marrow seedlings and the possible involvement of endogenous ethylene

Swelling of the hypocotyl base induced by 2,4-D in seedlings of marrow was much reduced if GA₃ was also present in the incubation medium. At appropriate concentrations kinetin also counteracted this 2,4-D effect, although at higher concentrations appeared to be ineffective. GA₃ was also able to overcome the inhibitory effects of 2,4-D on extension growth in the hypocotyl but kinetin was much less effective in this case. None of the treatments employed was able to alleviate the inhibition of radicle extension induced by 2,4-D.Ethephon induced similar responses in the seedlings to those resulting from 2,4-D treatment, while treatment with a mixture of 2,4-D and CoCl₂ removed many of these growth abnormalities. These observations are interpreted as indicating that 2,4-D operates at least partly by stimulating the production of ethylene in the tissues. 2,4-D strongly inhibited the accumulation of endogenous gibberellin during the period of seedling development examined, but enhanced cytokinin levels during the later stages of the same period. The possibility of interactions at the biosynthetic level between gibberellins, cytokinins and ethylene and their involvement in the regulation of seedling development are discussed.     

A comparative study of neurotensin inactivation by brain peptidases from different vertebrate species

The products formed from mammalian neurotensin by peptidases in two subcellular fractions from rat, mouse, dove, terrapin and goldfish brain were separated and identified using high-performance liquid chromatography. The main neurotensin metabolites were [1-8]-, [1-10]- and [1-7]-sequences; goldfish and terrapin brain fractions also produced [1-11]- and [1-12]-fragments. Avian neurotensin was cleaved by peptidases in rat and dove brain fractions to [1-8]-, [9-13]-, [1-10]- and [1-12]-fragments. Similar mechanisms of inactivation were found for both mammalian and avian neurotensins .     

The effects of adrenal and gonadal steroids and K+-canrenoate on the metabolism of aldosterone by rat liver microsomes

The synthesis of polar aldosterone metabolites by rat liver microsomes at physiological concentrations of aldosterone (21.5 nM), was markedly inhibited by progesterone, testosterone, corticosterone, K+-canrenoate and estradiol-17 beta. In contrast, corticosterone and estradiol-17 beta significantly increased the synthesis of reduced aldosterone metabolites by 8- and 15-fold respectively, the majority of which were 5 alpha-reduced products of aldosterone. In experiments at higher substrate (aldosterone) concentrations (20-200 microM) the synthesis of ring A-reduced aldosterone metabolites by liver microsomes followed Michaelis-Menten kinetics with a Km[app] for aldosterone of 160 microM and Vmax[app] of 12.2 nmoles/mg protein/5 min. In these experiments progesterone, testosterone and K+-canrenoate all competitively inhibited the synthesis of reduced metabolites with inhibition constants (Ki [app]) of 70, 85 and 55 microM respectively; however, corticosterone did not. In contrast, estradiol-17 beta increased the rate of synthesis of reduced products by 40%, lowering the Km[app] to 83 microM.     

Expectations of assisted conception for infertility.

OBJECTIVE--To provide reliable prognostic information for couples seeking assisted conception. DESIGN--Analysis of four years'' practice (1988-91). SETTING--Private university service linked with NHS reproductive medicine services. PATIENTS--804 couples with various causes of subfertility, median duration five years, median age of women 34 years. INTERVENTIONS--1280 completed cycles: 950 in vitro fertilisation, 144 gamete intrafallopian transfer, and 186 intrauterine insemination and superovulation. MAIN OUTCOME MEASURES--Pregnancy and birth rates per cycle and cumulative pregnancy and take home baby rates per couple. RESULTS--In women under 40 years and men with normal sperm, whatever the cause of infertility, results with in vitro fertilisation improved steadily reaching a pregnancy rate per cycle of 30% (95% confidence interval 26% to 35%) during 1990-1 and birth rate per cycle of 29% (23% to 35%) in 1990. Pregnancy and birth rates for gamete intrafallopian transfer were 36% (28% to 44%) and 26% (17% to 37%) and for intrauterine insemination 18% (12% to 24%) and 16% (10% to 22%). After six cycles cumulative probability of pregnancy was 82% and cumulative take home baby rate 70%. Considering only in vitro fertilisation and gamete intrafallopian transfer after four cycles the pregnancy rate was 78% (66% to 91%). CONCLUSIONS--Conception is less likely in women over 40 and men with sperm dysfunction. For other couples the prognosis for a live birth is at least as good as for fertile couples if they persist with treatment.     

Stimulation of ribosomal RNA synthesis during hypertrophic growth of cultured heart cells by phorbol ester

Primary cultures of neonatal cardiac myocytes were used to determine the effects of tumor-promoting phorbol esters on ribosomal RNA (rRNA) synthesis during myocyte growth. Treatment of myocytes with phorbol-12,13-dibutyrate (PDBu) increased protein accumulation by 25% and RNA content by 20%. Rates of rRNA synthesis were measured to assess the mechanism by which rRNA accumulated during myocyte growth. Rates of rRNA synthesis were determined from the incorporation of [³H]uridine into UMP of purified rRNA and the specific radioactivity of the cellular UTP pool. After 24h of PDBu treatment, cellular rates of 18S and 28S rRNA synthesis were accelerated by 67% and 64%, respectively. The increased rate of rRNA synthesis accounted for the net increase in myocyte rRNA content after PDBu treatment.     

The S3 state of photosystem II: differences between the structure of the manganese complex in the S2 and S3 states determined by X-ray absorption spectroscopy

O2-evolving photosystem II (PSII) membranes from spinach have been cryogenically stabilized in the S3 state of the oxygen-evolving complex. The cryogenic trapping of the S3 state was achieved using a double-turnover illumination of dark-adapted PSII preparations maintained at 240 K. A double turnover of PSII was accomplished using the high-potential acceptor, Q400, which is the high-spin iron of the iron-quinone acceptor complex. EPR spectroscopy was the principal tool establishing the S-state composition and defining the electron-transfer events associated with a double turnover of PSII. The inflection point energy of the Mn X-ray absorption K-edge of PSII preparations poised in the S3 state is the same as for those poised in the S2 state. This is surprising in light of the loss of the multiline EPR signal upon advancing to the S3 state. This indicates that the oxidative equivalent stored within the oxygen-evolving complex (OEC) during this transition resides on another intermediate donor which must be very close to the manganese complex. An analysis of the Mn extended X-ray absorption fine structure (EXAFS) of PSII preparations poised in the S2 and S3 states indicates that a small structural rearrangement occurs during this photoinduced transition. A detailed comparison of the Mn EXAFS of these two S states with the EXAFS of four multinuclear mu-oxo-bridged manganese compounds indicates that the photosynthetic manganese site most probably consists of a pair of binuclear di-mu-oxo-bridged manganese structures. However, we cannot rule out, on the basis of the EXAFS analysis alone, a complex containing a mononuclear center and a linear trinuclear complex. The subtle differences observed between the S states are best explained by an increase in the spread of Mn-Mn distances occurring during the S2----S3 state transition. This increased disorder in the manganese distances suggests the presence of two inequivalent di-mu-oxo-bridged binuclear structures in the S3 state.     

Photooxidation of specific residues in alpha-crystallin polypeptides

Singlet oxygen is a biologically important, photochemically generated species that preferentially oxidizes His, Trp, and Met residues of protein molecules. Calf alpha-crystallin was photooxidized with use of meso-tetra(p-sulfonatophenyl)porphyrin (TPPS) and uroporphyrin (UP) as singlet oxygen generators. The effects of photooxidation were monitored by analyzing the changes in alpha-crystallin peptide maps obtained by reversed-phase HPLC using a photodiode array absorbance detector. The reaction led to the loss of six specific peptides, five of which contained photooxidizable residues. Peptides containing His-97 and His-154 from the A chain and Met-68 from the B chain are preferentially photooxidized, suggesting that those residues have access to singlet oxygen. Trp residues in the N-terminal region are converted to NFK, whereas Trp-60 in the B chain is not photooxidized strongly suggesting that the former are close to the surface of alpha-crystallin while the latter Trp residue is buried. Only one peptide that is lost from the peptide maps does not contain a photooxidizable group; however, this peptide does contain an apparently undigested Lys residue. It is suggested that it forms a cross-link with a photooxidized His residue.     

Carbon metabolism in Bradyrhizobium japonicum bacteroids

Abstract Carbon metabolism in Bradyrhizobium japonicum bacteroids is reviewed. Additionally, the bacteroid tricarboxylic acid (TCA) cycle and its regulation under oxygen-limited conditions is considered, with emphasis on possible sites of TCA cycle rate-limiting reactions. Furthermore, we consider other adaptive pathways that may be employed by these organisms while in symbiosis. These pathways include: (1) a poly-β-hydroxy-butyrate shunt, (2) a malate-aspartate shuttle, (3) an α-ketoglutarate-glutamate shunt, (4) a modified dicarboxylic acid cycle, and (5) fermentation pathways leading to lactate, acetaldehyde and ethanol. The effects of oxygen limitation on host carbon metabolism are also considered briefly.     

Measurement of myosin adenosinetriphosphatase and myosin content in cultured heart cells

An assay specific for myosin ATPase in whole-cell extracts of cultured heart cells has been developed. Myosin ATPase is measured by the production of Pi from ATP in the presence of high ionic strength (0.5 M KCl) at pH 9.1. Enzyme activity is maximal with 10 mM CaCl2 and completely inhibited with 5 mM MgCl2. Spontaneously beating myocytes grown in the presence of 10% newborn calf serum and 0.1 mM 5-bromo-2'-deoxyuridine show a significant rise in myosin ATPase between Days 1 and 4 in culture. The measurement of myosin ATPase allows for the quantitation of cellular myosin content, and can be used to assess changes in myosin content that occur during growth, development, and cellular repair.