861. CYPRIPEDIUM FARGESII

Cypripedium fargesii Franch., an endangered species from West China, is described and illustrated. Notes on its discovery, taxonomy, habitat, conservation status, and cultivation are provided.     

The use of fluorometry for on-line measurement of mixing time and hold-up in fermentations

Summary Mixing times and gas hold-ups in a 250L bioreactor containing a phosphate buffer or an active fermentation were determined on-line using fluorometric (MEFS and NADH) probes as functions of agitation and aeration rates. Both mixing time and hold-up of a fermentaion can be determined using a MEFS probe. Hold-up may also be measured with a presently available commercial NADH probe.     

Which Is Better: Holdout or Full-Sample Classifier Design?

Is it better to design a classifier and estimate its error on the full sample or to design a classifier on a training subset and estimate its error on the holdout test subset? Full-sample design provides the better classifier; nevertheless, one might choose holdout with the hope of better error estimation. A conservative criterion to decide the best course is to aim at a classifier whose error is less than a given bound. Then the choice between full-sample and holdout designs depends on which possesses the smaller expected bound. Using this criterion, we examine the choice between holdout and several full-sample error estimators using covariance models and a patient-data model. Full-sample design consistently outperforms holdout design. The relation between the two designs is revealed via a decomposition of the expected bound into the sum of the expected true error and the expected conditional standard deviation of the true error.     

Detecting Periodic Genes from Irregularly Sampled Gene Expressions: A Comparison Study

Time series microarray measurements of gene expressions have been exploited to discover genes involved in cell cycles. Due to experimental constraints, most microarray observations are obtained through irregular sampling. In this paper three popular spectral analysis schemes, namely, Lomb-Scargle, Capon and missing-data amplitude and phase estimation (MAPES), are compared in terms of their ability and efficiency to recover periodically expressed genes. Based on in silico experiments for microarray measurements of Saccharomyces cerevisiae, Lomb-Scargle is found to be the most efficacious scheme. 149 genes are then identified to be periodically expressed in the Drosophila melanogaster data set.     

Conserved WCPL and CX4C Domains Mediate Several Mating Adhesin Interactions in Saccharomyces cerevisiae

Several adhesins are induced by pheromones during mating in Saccharomyces cerevisiae, including Aga1p, Aga2p, Sag1p (Agα1p), and Fig2p. These four proteins all participate in or influence a well-studied agglutinin interaction mediated by Aga1p–Aga2p complexes and Sag1p; however, they also play redundant and essential roles in mating via an unknown mechanism. Aga1p and Fig2p both contain repeated, conserved WCPL and CX₄C domains. This study was directed toward understanding the mechanism underlying the collective requirement of agglutinins and Fig2p for mating. Apart from the well-known agglutinin interaction between Aga2p and Sag1p, three more pairs of interactions in cells of opposite mating type were revealed by this study, including bilateral heterotypic interactions between Aga1p and Fig2p and a homotypic interaction between Fig2p and Fig2p. These four pairs of adhesin interactions are collectively required for maximum mating efficiency and normal zygote morphogenesis. GPI-less, epitope-tagged forms of Aga1p and Fig2p can be co-immunoprecipitated from the culture medium of mating cells in a manner dependent on the WCPL and CX₄C domains in the R1 repeat of Aga1p. Using site-directed mutagenesis, the conserved residues in Aga1p that interact with Fig2p were identified. Aga1p is involved in two distinct adhesive functions that are independent of each other, which raises the possibility for combinatorial interactions of this protein with its different adhesion receptors, Sag1 and Fig2p, a property of many higher eukaryotic adhesins.     

Simple and selective high-performance liquid chromatographic method for estimating plasma quinidine levels

A reversed-phase, high-performance liquid chromatographic method employing fluorescence detection is described for the rapid quantification of plasma levels of quinidine, dihydroquinidine and 3-hydroxyquinidine. It involves protein precipitation with acetonitrile followed by direct injection of the supernatant into the chromatograph. For the preparation of plasma standards, pure 3-hydroxyquinidine was isolated from human urine by a simplified thin-layer chromatographic procedure. The mobile phase for the chromatography was a mixture of 1.5 mM aqueous phosphoric acid and acetonitrile (90:10) at a flow-rate of 2 ml/min. The intra-assay coefficient of variation for the assay of quinidine and 3-hydroxyquinidine over the concentration range 2.5–20 μmole/l was < 1% for both. Interassay coefficients of variation for quinidine (10 μmole/l) and 3-hydroxyquinidine (5 μmole/l) were 3.5% and 4.0% with detection limits of 50 and 25 μmole/l respectively. The method correlated well (r² = 0.96) with an independently developed gas—liquid chromatographic—nitrogen detection assay for quinidine which also possessed a high degree of precision. (Intra-assay coefficient of variation 3.6% at 20 μmole/l). As expected, comparison of the high-performance liquid chromatographic assay with a published protein precipitation—fluorescence assay showed poor correlation (r² = 0.78).