Resonance Raman spectra of chlorophylls dissolved in liquid crystal matrices. II. Order parameters of chlorophyll a in an MBBA + EBBA liquid crystalline mixture

The molecular ordering of molecules embedded in a uniaxial liquid crystalline system has been considered. In particular, planar Chl a molecules in an MBBA + EBBA mixture have been studied by using polarized resonance Raman spectroscopy. The second- and fourth-rank order parameters and the orientational distribution function of Chl a in the nematic MBBA + EBBA liquid crystalline phase are discussed.     

Strain Improvement of Rhodotorula graminis for Production of a Novel l-Phenylalanine Ammonia-Lyase

l-Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) from Rhodotorula rubra has been used in the commercial manufacture of l-phenylalanine from trans-cinnamic acid. In this study, R. graminis PAL was investigated. Mutant strain GX6000 was isolated after ethyl methanesulfonate mutagenesis of wild-type R. graminis GX5007 by selecting for resistance to phenylpropiolic acid, an analog of trans-cinnamic acid. Mutant strain GX6000 produced inducible PAL at levels four- to fivefold higher than had wild-type R. graminis. Furthermore, this strain had several other physiological traits that make it more commercially useful than R. rubra. For example, during fermentation, the PAL half-life was three- to fivefold longer, PAL specific activity was six to seven times higher, and PAL synthesis was significantly less inhibited by temperatures above 30 degrees C. Induction of PAL in strain GX6000 appeared to be less tightly regulated; l-leucine acted synergistically with l-phenylalanine, the physiological inducer, to increase the PAL specific activity and titer to 165 U/g (dry weight) and 3,000 U/liter, respectively, a 40% increase over the effect of l-phenylalanine alone. Strain GX6000 PAL showed significantly greater stability in bioreactors for the synthesis of l-phenylalanine, a finding that is consistent with the stability properties observed during fermentation.     

Ovulatory response and embryo yield in superovulated holstein heifers given a priming dose of FSH-P at day 2 of the estrous cycle

Mature Holstein heifers were given either a priming dose of follicle-stimulating hormone-pituitary (FSH-P, 10 mg) or saline on Day 2 of the estrous cycle, or no pretreatment. All animals were subsequently given a decreasing dose superovulatory treatment of FSH-P beginning between Days 8 and 14, coupled with an injection of prostaglandin F2a to induce luteolysis. Pretreatment with FSH-P had no effect on the total superovulatory response or on the number of transferable embryos collected at Day 7 of gestation. Comparison of the results of our study with previous reports in the literature may suggest that FSH-priming early in the cycle may be advantageous in promoting superovulation only when the superovulatory response of the population of animals is otherwise weak.     

Influence of follicular components on oocyte meiosis in vitro

Oocytes and follicular components obtained from ovaries recovered from mature Hereford cows at slaughter were used to determine follicular influence on oocyte maturation. Some oocytes were fixed immediately to determine the stage of maturation. The remaining oocytes were cultured for 32 to 34 hr in various environments to determine the influences of the granulosum and follicular fluids on meiotic changes. All noncultured oocytes had dictyate nuclei except one in premetaphase. Oocytes cultured in 50 or 100% follicular fluid or in contact with stratum granulosum cells showed some meiotic inhibition both before and after germinal vesicle breakdown (GVB). The least resumption of meiosis occurred in oocytes cultured in their intact follicles.     

Dermatobia, the neotropical warble fly

The neotropical warble fly, Dermatobia hominis (Fig. 1), has plagued neotropical America since preColombian times, and has become an economically important pest causing substantial losses to the meat, milk and leather industries from northern Mexico down to northern Argentina. Its life cycle (Box 1) is astonishingly complex, requiring another insect as a phoretic carrier of its eggs to the skin of its mammal hosts. Here Eugenio Sancho discusses factors that contribute to the current economic and public health importance of this myiasis-causing fly.     

Did medicated salt hasten the spread of chloroquine resistance in Plasmodium falciparum?

With acknowledged difficulties in achieving satisfactory compliance rates for the large-scale delivery of many antiporositic drugs, the use of medicated salt has often been seen as a useful way to improve the level o f treatment in target populations. Iodinated salt is said to have contributed to a decline in endemic goitre, and salt medicated with chloroquine and/or other antimalorials, or with diethylcarbomazine, has been widely used in public health programmes against malaria and filariosis respectively. In this article, however, David Payne suggests that chloroquinized salt programmes may have been a major factor in promoting chloroquine resistance in Plasmodium falciparum.     

Mobilization and utilization of cyanogenic glycosides: the linustatin pathway

In the seeds of Hevea brasiliensis, the cyanogenic monoglucoside linamarin (2-β-d-glucopyranosyloxy-2-methylpropionitrile) is accumulated in the endosperm. After onset of germination, the cyanogenic diglucoside linustatin (2-[6-β-d-glucosyl-β-d-glucopyranosyloxy]-2- methylpropionitrile) is formed and exuded from the endosperm of Hevea seedlings. At the same time the content of cyanogenic monoglucosides decreases. The linustatin-splitting diglucosidase and the β-cyanoalanine synthase that assimilates HCN, exhibit their highest activities in the young seedling at this time. Based on these observations the following pathway for the in vivo mobilization and metabolism of cyanogenic glucosides is proposed: storage of monoglucosides (in the endosperm)—glucosylation—transport of the diglucoside (out of the endosperm into the seedling)—cleavage by diglucosidase—reassimilation of HCN to noncyanogenic compounds. The presence of this pathway demonstrates that cyanogenic glucosides, typical secondary plant products serve in the metabolism of developing plants as N-storage compounds and do not exclusively exhibit protective functions due to their repellent effect.     

Overwintering Periwinkle (Vinca minor L.) Exhibits Increased Photosystem I Activity

The effects of natural, overwintering conditions on photosystem I and photosystem II activity were examined in isolated thylakoids of periwinkle (Vinca minor L.), an endemic, cold-tolerant, herbaceous evergreen. DCMU-Insensitive photosystem I activity (ascorbate/dichlorophenolindophenol → methylviologen) exhibited a twofold increase in light-saturated rates upon exposure to low temperature and freezing stress with no effect on the apparent quantum yield of this reaction. DCMU-Sensitive photosystem II activity (H₂O → dichlorlophenolindophenol) exhibited only minor fluctuations in light-saturated rates but a 50% decrease in the apparent quantum yield of this reaction upon exposure to overwintering conditions. This was correlated with a decrease in the 77°K fluorescence emission at 694 nanometers. These functional changes occurred with no detectable changes in the relative chlorophyll contents of the chlorophyll-protein complexes or the chlorophyll-thylakoid protein. The chlorophyll a/b varied less than 10% during any single growth year. Analyses of total leaf extracts indicated that all lipid classes exhibited increased levels of linoleic and linolenic acid. Neither the trans-Δ³-hexadecenoic acid level nor the ratio of oligomeric:monomeric light harvesting of photosystem II was affected by exposure to winter stress. The content of the major chloroplast lipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidyl-diacyl-glycerol, and sulfoquinovosyldiacylglycerol exhibited minor fluctuations, whereas phosphatidylcholine and phosphatidylethanolamine content doubled on a mole percent or chlorophyll basis. We conclude that the previously reported increase in photosystem I activity during controlled, low temperature growth is observed during exposure to natural overwintering conditions. This appears to occur with minimal changes in the structure and composition of the photosynthetic apparatus of periwinkle.     

First evidence for polyamine conjugation mediated by an enzymic activity in plants

An enzyme activity, found for the first time in plants, mainly located in the 22,000g supernatant of the crude extract of sprout apices of Helianthus tuberosus L. cv OB1 tubers, is able in vitro to covalently bind polyamines to endogenous substrates of different molecular weights. The major assay parameters, such as pH, dithiothreitol, and extract concentrations were optimized. The time course of the reaction, the dependence on putrescine concentration, its competition with histamine, the capacity to bind spermidine and spermine better than putrescine, the stability of the reaction product and analysis of the latter by sodium dodecyl sulfate polyacrylamide gel electrophoresis and thin-layer chromatography suggest that putrescine is linked to endogenous substrates by means of an enzyme reaction that shows some similarities with transglutaminase activities detected in animals. However, the activities of the crude extract and of a fraction eluted from a Sephadex G25 column were not affected by CaCl₂ concentrations lower or equal to 5 millimolar; 4 or 10 millimolar EGTA caused a very small reduction; higher concentrations of CaCl₂ and 15 millimolar or more of EDTA were inhibitory. N,N′-dimethylcasein was not recognized as a substrate. These data indicate that this activity also displays some characteristics which are different from those of animal transglutaminases.