Regulation of diurnal filter feeding by a novel gill structure in Amblypharyngodon melettinus (Teleostei,Cyprinidae)

A unique gill structure, apparently associated with filter feeding on phytoplankton and suspended microdetritus, has been found in Amblypharyngodon melettinus, an abundant small Cyprinidae of Sri Lanka. The gill lamellae, the site of gas exchange, are bordered by a double row of fine appendices which are spread over the interlamellar gaps during daytime, but folded up at night. A respiratory function of the appendices can be excluded. The changing position of appendices correlates with the diurnal pattern of feeding (day) and swimming (night). The mechanism for movement of the appendices consists of hinge-like joints formed from the basement membranes of pavement cells, driven by variation in lamellar blood pressure. Food collection is based on both an efficient hydrosol filter produced by dense populations of clavate mucous cells of the buccopharyngeal epithelia and the lamellar appendices which cause a slower and more turbulent water current in the buccopharyngeal cavity. This may ensure the proper contact of food particles with the sticky mucous surface before they leave the buccopharyngeal cavity. The uniqueness of this structure is that the filter can be switched off during periodically occurring periods of high oxygen demand (high swimming activity at night) probably benefiting the process of respiration.     

Problems in the Cultivation of Winter Lettuce

In a four-year study of winter lettuce cultivation, attention has been given to the effects of variety, dates of sowing and transplanting, method of preparing seed-beds, nature of field soil, and fungicidal treatments upon percentage survival and date of maturity of the crop
The inferiority of the variety Trocadero Improved to such a winter variety as Imperial is due mainly to its susceptibility to Pythium root rot. This disease often causes severe thinning of the stand of Trocadero seedlings and dwarfing of many of the survivors
Late autumn plantings of Imperial and other winter varieties survived better overwinter on a medium-heavy loam than on a light sandy soil. The disparity varied in different seasons and was not associated with severity of winter
The dates of maturity of the crop in relation to dates of sowing and transplanting have been determined over the four-year period. On the basis of these, and on the records of survival and of market prices, an estimate can be obtained of the financial aspects of different cultural methods
Fungicidal treatment in the seed-bed of plants set out in the field in November gave little improvement in survival; but pronounced benefit was obtained by February or March dusting of seedlings which had overwintered in the seed-bed
The onset of disease in overwintering seed-beds was found to be influenced by the nature of the soil and by the manner of preparation of the seed-bed
The interrelations of overwintering and soil type are briefly discussed, with special reference to the effects of soil type (i) on the root system, and (ii) on microbiological interference with invasion of die stem by Botrytis     

Liposome-mediated delivery of pteridine antifolates to cells in vitro: potency of methotrexate, and its alpha and gamma substituents

We have examined the growth-inhibitory potency of several pteridines encapsulated in negatively charged liposomes, including methotrexate, methotrexate-gamma-methylamide, methotrexate-gamma-dimethylamide, methotrexate-alpha-aspartate, and a lipophilic methotrexate-phosphatidylethanolamine conjugate. The potency of encapsulated methotrexate is greater than the potency of the free drug for CV1-P cells, but not for other cell lines. The potency of methotrexate-gamma-methylamide and methotrexate-gamma-dimethylamide is only minimally improved by encapsulation. The potency of methotrexate-alpha-aspartate is increased by encapsulation. In addition, the lipophilic methotrexate derivative has demonstrable potency when incorporated in liposomes. We have also examined the potency of several pteridines under conditions where the cells are exposed to the drug for periods shorter than the entire growth assay. Reduction of the exposure time decreases the potency of both encapsulated and free drugs. However, the difference in potency between the encapsulated and free drug is increased, because the potency of the encapsulated drug is affected less. Consequently, encapsulated methotrexate-gamma-aspartate is 300-fold more potent than free drug, if CV1-P cells are exposed to drug for 4 h. Moreover, encapsulated methotrexate is more potent than free methotrexate for growth inhibition of L929 fibroblasts, if the term of exposure is less than 8 h. Potency is least affected by reduction of exposure length for the lipophilic methotrexate derivative.     

Proteases as catalytic agents in peptide synthetic chemistry: Shifting the extent of peptide bond synthesis from a “quantité négligeable” to a “quantité considérable”

Under ordinary conditions the equilibrium point in protease-catalyzed reactions is near to complete hydrolysis. Therefore, proteases are commonly known for their proteolytic rather than for their proteosynthetic activities. Nevertheless, the proteases have proved to be excellent catalysts in preparative peptide synthetic chemistry. A brief review is given of the historical development of protease-catalyzed peptide synthesis. The theoretical aspects of peptide bond formation are described and particular emphasis is given to techniques for favoring the synthesis of the desired peptide linkages. The applicability of these techniques is exemplified with selected syntheses and semisyntheses. The advantages as well as the problems associated with the enzymatic method are evaluated. A critical assessment is given of the present state of the art and the perspectives of the enzymatic approach to peptide synthetic chemistry.     

Hierarchical role of fetuin-A and acidic serum proteins in the formation and stabilization of calcium phosphate particles

The serum protein fetuin-A is a potent systemic inhibitor of soft tissue calcification. Fetuin-A is highly effective in the formation and stabilization of protein-mineral colloids, referred to as calciprotein particles (CPPs). These particles ripen in vitro in a two-step process, indicated by a morphological conversion from spheres to larger prolate ellipsoids. Using a combined light scattering and electron microscopic imaging approach we determined that the second-stage particles resulted from a highly anisotropic outgrowth of the first-stage particles. Electron microscopy of ascites fluid from a patient with calcifying peritonitis revealed particles reminiscent of secondary CPPs. Thus, CPPs form in the body and undergo the two-step ripening at least in pathological conditions. Unlike in vitro generated CPPs, ascites-derived CPPs contained little fetuin-A but large amounts of albumin. This prompted us to study the role of fetuin-A combined with other serum proteins in CPP formation. Fetuin-A was indispensable for primary CPP formation. Albumin and acidic proteins in general greatly enhanced the fetuin-A triggered formation of secondary CPPs and, thus, substituted substantial amounts of fetuin-A without loss of inhibition of calcium phosphate precipitation. Thus, direct mineral deposition from solute in the body is unlikely even at low fetuin-A serum levels as long as sufficient bulk acidic protein is available. Collectively fetuin-A and other acidic bulk plasma proteins may be considered as mineral chaperones mediating the stabilization, safe transport, and clearance in the body of calcium and phosphate as colloidal complexes, thus, preventing ectopic calcification.