Ethylene production and β-cyanoalanine synthase activity in carnation flowers

The relationship between ethylene production and the CN^--assimilating enzyme -cyanoalanine synthase (CAS; EC 4.4.1.9) was examined in the carnation (Dianthus caryophyllus L.) flower. In petals from cut flowers aged naturally or treated with ethylene to accelerate senescence the several hundred-fold increase in ethylene production which occurred during irreversible wilting was accompanied by a one- to twofold increase in CAS activity. The basal parts of the petal, which produced the most ethylene, had the highest CAS activity. Studies of flower parts (styles, ovaries, receptacles, petals) showed that the styles had a high level of CAS together with the ethylene-forming enzyme (EFE) system for converting 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The close association between CAS and EFE found in styles could also be observed in detached petals after induction by ACC or ethylene. Treatment of the cut flowers with cycloheximide reduced synthesis of CAS and EFE. The data indicate that CAS and ethylene production are associated, and are discussed in relation to the hypothesis that CN^- is formed during the conversion of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglyoine - CAS -cyanoalanine synthase - CHI cycloheximide - EFE ethylene-forming enzyme     

The pH dependence of hydrogen exchange in proteins

The static accessibility modified discrete charge model for electrostatic interactions in proteins is extended to the prediction of the pH dependence of hydrogen exchange reactions. The exchange rate profiles of buried amide protons are shown to follow the calculated pH dependence of the electrostatic component of protein stability. Rate profiles are calculated for individual buried amide protons in ribonuclease S and bovine pancreatic trypsin inhibitor. The electrostatic free energy of stabilization of the protein and the energy required to bring the catalytic ion to an exchange site are expressed as an apparent, pH-dependent contribution to the activation energy. Changes in the electrostatic stabilization of the proteins affect the calculated exchange rate for buried amide protons by more than 1000, while local field effects raise or lower the predicted exchange rates by less than 100. The pH dependence of exchangeable protons at the protein surface, such as the C-2 imidazole protons, is shown to follow the estimated energy required to introduce the catalytic ion at the exchange site. These calculations are discussed in terms of current models for proton exchange which incorporate the dynamic nature of the structure to explain exchange data from the interior of a protein.     

Neutral and Acid Sphingomyelinases of Rat Brain: Somatotopographical Distribution and Activity Following Experimental Manipulation of the Dopaminergic System In Vivo

The activities of neutral, magnesium-stimulated, and acid sphingomyelinases were measured in five regions of rat brain. Neutral enzyme activity was 2-3-fold higher in striatum than in parietal cortex and 13-fold higher than in cerebral white matter. Acid sphingomyelinase activity was more evenly distributed throughout these regions. Striatal neutral sphingomyelinase activity was not affected by treatment of rats with reserpine or haloperidol and was reduced (16%) by 6-hydroxydopamine. Striatal acid sphingomyelinase was unaffected by reserpine and 6-hydroxydopamine, and was increased (17%) by haloperidol. We conclude that neutral, magnesium-stimulated sphingomyelinase activity differs in various regions of rat brain and is particularly enriched in the corpus striatum. However, it appears to be a constitutive component of tissue rather than a readily modulated regulatory element of the catecholaminergic system.     

Detergent Effects on the Phosphatidylinositol-Specific Phospholipase C in Rat Brain Synaptosomes

In the presence of Ca2+ (2.5 mM) and using [14C]arachidonoyl phosphatidylinositol (PI) membrane as substrate, phosphatidylinositol-specific phospholipase C (PI-PLC) (EC 3.1.4.10) in rat brain synaptosomes was activated by deoxycholate but not taurocholate. Calcium stimulated enzymic hydrolysis by both detergents, but the stimulatory effect of taurocholate was less than that of deoxycholate. Peak stimulation for deoxycholate was observed at 1 mg/ml, whereas that for taurocholate was 4 mg/ml. When 1 mM EDTA was added to the taurocholate (4 mg/ml) and Ca2+ (3.5 mM) system, synaptosomal PI-PLC activity was greatly stimulated, to almost the same level as the deoxycholate + Ca2+ system. This system required the presence of all three factors, and EGTA could not effectively replace EDTA in the stimulatory action. The detergent-induced hydrolysis of synaptosomal PI by the deoxycholate + Ca2+ and the taurocholate + Ca2+ + EDTA systems was strongly inhibited by divalent metal ions such as Zn2+, Cu2+, Pb2+, and Fe2+, whereas Mg2+ and Ca2+ were ineffective. Nevertheless, only the deoxycholate + Ca2+ system was responsive to enzyme inhibition by membrane-perturbing agents such as lysophospholipids and free fatty acids. The specific requirement for EDTA in the taurocholate system may be due to the release of a pool of inhibitory divalent metal ions from the membranes.     

Growth and lipolysis of rat adipose tissue: effect of age, body weight, and food intake

The purpose of the present work was to study age- and weight-controlled rats to determine which is the primary factor in reducing the lipolytic response of free fat cells and which has the greater effect on the ratio of fat cells to nonfat cells in adipose tissue. The method for estimating fat cell and nonfat cell numbers is based on the analysis of adipose tissue and fat cell DNA and lipid. In adequately fed rats, epididymal adipocyte hyperplasia is complete between 9 and 14 wk of age. Chronic underfeeding delays, but does not eliminate, normal fat cell hyperplasia and is accompanied by a net loss in the nonfat cell population. During 9-14 wk of age, rat epididymal adipose tissue enlarges mainly through adipocyte hypertrophy. Total fat cells from the epididymal adipose tissue of control rats represent only 20-23% of the total cell population. Chronic underfeeding increases the percentage of fat cells in the fat pad from 23 to 28%. Noradrenaline-stimulated lipolysis is proportional to fat cell numbers but is inhibited when fat cell lipid increases to over 80% of fat pad wet weight. Rat age is apparently not primarily responsible for the decreased noradrenaline-stimulated lipolysis in fat cells of 350-g rats in vitro.     

Neonatal androgen and sexual behavior in female house mice

A series of experiments investigated masculine response potential in normal BDF₁ female mice and in females who had been injected with 100 μg of testosterone propionate on the day of birth. Sixty-five percent of BDF₁ females mounted females in estrus; ovariectomy lowered this response potential while injections of TP in adulthood raised masculine RP in both ovariectomized and intact females. Neonatally androgenized females with or without TP in adulthood exhibited the full range of masculine responses including the ejaculatory reflex. Comparisons of elements of sexual behavior are made between neonatally androgenized females and normal males.     

The enzymic and non-enzymic degradation of colneleic acid, an unsaturated fatty acid ether intermediate in the lipoxygenase pathway of linoleic acid oxidation in potato (Solanum tuberosum) tubers

Colneleic acid is an unsaturated ether fatty acid derived from linoleic acid via a lipoxygenase-mediated enzyme pathway. It is degraded (a) by an enzyme in potato tubers which is heat-labile and non-dialysable and (b) by a model system containing catalytic amounts of Fe(2+) ions. Both enzyme- and Fe(2+)-catalysed systems have similar properties with respect to pH optima (pH5.0-5.5), oxygen requirement (0.6-0.7 mol of O(2) consumed/mol of ether degraded), inhibitors and reaction products. An unstable product breaks down to C(8) and C(9) carbonyl fragments. Both systems are inhibited by low concentrations of antioxidants (e.g. 5mum-butylated hydroxytoluene) and some chelating agents (e.g. 5mum-diethyldithio-carbamate). The model system is strongly inhibited by metal ions, particularly Cu(2+) and Fe(3+), at 20mum. Hydrogen peroxide and haemoproteins do not substitute for the enzyme or Fe(2+) ions but the non-haem iron protein, ferredoxin, does catalyse the degradation.     

In Vitro Antimicrobial Activity and Human Pharmacology of Cephalexin, a New Orally Absorbed Cephalosporin C Antibiotic

Concentrations of cephalexin (an orally absorbed derivative of cephalosporin C) in serum and urine were determined in normal volunteers and patients. The in vitro antibacterial activity was also studied. All strains of group A β-hemolytic streptococci and Diplococcus pneumoniae were inhibited by 3.1 μg/ml. Of the Staphylococcus aureus strains, 88% were inhibited by 6.3 μg/ml, and 12.5 μg/ml was inhibitory for all S. aureus, 80% of Escherichia coli, 72% of Klebsiella-Aerobacter, and 56% of Proteus mirabilis strains. About 90 to 96% of E. coli, Klebsiella Aerobacter, and P. mirabilis strains were inhibited by 25 μg of cephalexin per ml. Pseudomonas and indole-positive Proteus strains proved to be quite resistant to cephalexin. Cephalexin was well absorbed after oral administration. A peak serum concentration of cephalexin of at least 5 μg/ml was achieved in each volunteer with 250 and 500-mg doses. A mean peak serum concentration of 7.7 μg/ml was achieved with 250-mg doses; 12.3μg/ml was achieved with 500-mg doses of antibiotic. Food did not interfere with absorption. Probenecid enhanced both the peak serum concentration and the duration of antibiotic activity in the serum. Over 90% of the administered dose was excreted in the urine within 6 hr. The mean peak serum concentration of cephalexin after an oral dose of 500 mg was adequate to inhibit all group A streptococci, D. pneumoniae, and S. aureus, 85% of E. coli, and about 40 to 75% of Klebsiella-Aerobacter and P. mirabilis strains. Levels of cephalexin in urine were adequate to inhibit over 90% of E. coli, and P. mirabilis and 80 to 96% of Klebsiella-Aerobacter strains.