Slow O,N-acyl shift in an actinomycin-related peptide lactone

The pentapeptide lactone Cbz-(Thr-D-Val-Pro-Sar-MeAla-) was synthesized in order to observe the behavior of the unprotected lactone resulting from its hydrogenolytic deprotection. Closely related peptide lactones have been reported as intermediates in total syntheses of actinomycin D and its analogues, despite the fact that unprotected and unprotonated O-peptides of serine and threonine are known to undergo rapid O,N-acyl shift. In the present study the peptide lactone was seen to undergo a slow O,N-acyl shift, in a matter of hours, to the known cyclic pentapeptide. This contrasted with the rapid rearrangement of a model O-peptide, O-hippuryl-L-threonine methyl ester. This slowness of an O,N-acyl shift in a cyclic system presumably results from higher energy barriers of conformational origin. It explains the suitability of unprotected peptide lactones for the syntheses of actinomycins and other peptide lactone antibiotics which have appeared in the literature.     

RNA editing in mitochondrial mRNA of trypanosomatids.

The editing of mRNA coding sequences by the modification, removal or addition of nucleotides has recently been recognized as another form of RNA processing. Studies of the extensive editing of mitochondrial mRNAs in trypanosomatids have revealed the involvement of small guide RNAs (gRNAs) which are encoded by the minicircles of kinetoplast DNA.     

Immature Stages and Hosts of Two Plesiomorphic,Antillean Genera of Membracidae (Hemiptera) and a?new species of Antillotolania from Puerto Rico

The nymphs of Antillotolania Ramos and Deiroderes Ramos are described for the first time, along with the first host record for the genus Antillotolania, represented by Antillotolania myricae, sp. n. Nymphal features of both genera, such as a ventrally fused, cylindrical tergum IX (anal tube), the presence of abdominal lamellae, and heads with foliaceous ventrolateral lobes confirm their placement in Membracidae and are consistent with phylogenetic analyses placing them in Stegaspidinae but in conflict with a cladistic analysis showing a closer relationship to Nicomiinae. Head processes and emarginate forewing pads in the last instars of both genera support an earlier estimate, based on nuclear genes, that the two genera form a monophyletic group in Stegaspidinae. Distinguishing features of the four species of Antillotolania are tabulated.     

Histo- and cytophysiology of the lactating mammary gland of the African elephant (Loxodonta africana)

The lactating mammary gland of the African elephant (Loxodonta africana) has been studied with a panel of morphological techniques focusing on (1) the functional changes during the secretory process, (2) proliferative process [by application of proliferating cell nuclear antigen (PCNA) immunohistochemistry] and apoptotic phenomena [by use of the TUNEL technique] in the individual lobules, and (3) components of milk and milk-fat-globule membrane. In the lactating gland, the lobules are variably differentiated; within a lobule, however, the alveoli are usually similarly differentiated. The morphology of their alveoli suggests a classification of the lobules into types 1–3. Lobules of type 1 are composed of immature tubular alveoli with mitotic figures and numerous PCNA-positive nuclei; advanced type 1 alveoli contain abundant glycogen and specific secretory granules. Lobules of type 2 are further subdivided. In type 2a lobules, the epithelial cells of the alveoli form tall apical protrusions, which in part are occupied by small lipid droplets and which are pinched off in an apocrine fashion. The number of lysosomes varies considerably. Type 2b is the most common type, with striking basal membrane foldings, abundant rough endoplasmic reticulum cisterns, large Golgi apparatus, numerous mitochondria, lipid droplets, and protein vesicles with 30- to 90-nm-wide casein micelles. The lipid droplets are pinched off with minimal amounts of cytoplasm. Type 2c is composed of alveoli with a cuboidal epithelium and few signs of secretory activity. Increasing expression of peanut-agglutinin-binding sites parallels the maturation and differentiation of the glandular cells. Type 3 lobules are marked by numerous TUNEL-positive nuclei and large lipid droplets and are apparently degenerating structures. Cytokeratin (CK) 14 is usually present in the myoepithelial cells; CK 19 and CK 7 mark ductal and immature alveolar epithelia. Milk protein content varies between 2.6% and 6.3%, and casein micelles range from 35 to 90 nm in diameter. The diameter of intra-alveolar milk fat globules ranges from 5 to 25 µm and the membranes bear a filamentous surface coat composed of membrane-anchored mucins; gel-electrophoretic analysis of these mucins from different individuals demonstrates the presence of mucin MUC 1, which is expressed with considerable genetic heterogeneity.     

Effects of an invasive bivalve on the zooplankton community of the Hudson River

1. Previous studies documented that zebra mussels became abundant in the Hudson River during 1992 causing an 80–90% reduction in phytoplankton biomass. This study used intervention time series analysis of abundance, biomass and reproduction over the period 1987–95 to assess changes in zooplankton in response to the invasion.
2. Zebra mussels caused a size-dependent decline in zooplankton. Microzooplankton, including tintinnid ciliates, rotifers and copepod nauplii all declined in 1992 and were scarce thereafter. Mean abundances of post-naupliar copepods and of cladocerans were also lower following the invasion but these changes were not statistically significant ( P > 0.05). Egg ratios and clutch sizes for the dominant cladoceran, Bosmina freyi , were not significantly related to zebra mussels, even though relatively low egg ratios were observed after the invasion.
3. The strong declines in microzooplankton were probably caused by direct zebra mussel predation. Estimated consumption rates by mussels were roughly equivalent to maximum microzooplankton growth rates.
4. The total biomass of zooplankton in the Hudson River declined by more than 70% following the invasion. Annual average zooplankton biomass was correlated with chlorophyll, but biomass per unit chlorophyll in the Hudson River was much lower than in lakes. The present study hypothesizes that this lower biomass reflects limitations by riverine flow and by predation during summer.     

Separation and quantitation ofcis- andtrans-thiothixene in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic procedure is described for the separation ofcis andtrans isomers of thiothixene, a thioxanthene derivative used as an antipsychotic agent. A radial compression module (RCM-100) was used with both silica and cyanopropyl cartridges. A fixed-wavelength UV detector (254 nm) was used in these studies for quantitation. Mesoridazine is used as an internal standard because of its separation characteristics and reproducible quantitation. C₁₈ Sep-Pak cartridges are used for biological sample cleanup. Plasma samples from patients treated with thiothixene (Navane) were assayed forcis andtrans-thiothixene. Notrans-thiothixene was detectable andcis-thiothixene concentrations ranged from 0 to 22.5 ng/ml.