Photopolymerized phospholipid vesicles Stability and retention of hydrophilic and hydrophobic marker substances

Multilamellar vesicles were formed from photopolymerizable analogs of phosphatidylcholine. The polymerized vesicles differed markedly from conventional vesicles in terms of their stability to mechanical and chemical perturbations. Thus, polymerized vesicles, but not conventional ones, retained their overall physical integrity subsequent to ultrasonication or to exposure to organic solvents or detergents. Treatment of photopolymerized vesicles with detergents such as sodium dodecyl sulfate caused the release of entrapped hydrophilic solutes; however, lipophilic solutes were retained by the polymerized vesicles under circumstances in which conventional vesicles were completely solubilized. Thus, photopolymerized phospholipid membranes represent hybrid entities which seem to blend some of the characteristics of conventional lipid bilayers with properties more typical of polymer membranes.     

The cleavage of the Met-Lys bond in a bradykinin derivative by glandular kallikreins

The synthetic tridecapeptide Gly-Leu-Met-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg was used as a model substrate for horse urinary and porcine pancreatic kallikreins. The Met-Lys bond is hydrolyzed selectively by both enzymes. Oxidation of the methionine residue to sulfoxide made the peptide resistant to both kallikreins. Substitution of either the methionine or lysine residues by norleucine led to peptides in which the Nle-Lys or the Met-Nle bonds, respectively, were susceptible to the urinary kallikrein. The esterolytic and Met-Lys bond-splitting activities of both enzymes were inhibited similarly by phenylmethanesulfonyl fluoride. Both activities of the pancreatic kallikrein were inhibited by the chloromethane derivative Ala-Leu-Lys-CH2Cl. Inhibition by benzamidine of Met-Lys hydrolysis by both kallikreins was observed.     

Reduction of ortho-aminobenzoyl-proline fluorescence and formation of pyrrolobenzodiazepine-5,11-dione

The ortho-aminobenzoic acid (Abz) group is widely employed as a fluorescent marker for peptides used as substrates for the study of proteolytic enzyme activity. In fact, a direct correlation has been observed between fluorescence intensity and enzyme activity. An unusual behavior of the fluorescence properties of this group, which would lead to erroneous evaluation of the enzyme activity, was observed when it is bound directly to proline. Here we report a systematic NMR, fluorescence and X-ray diffraction study of the compounds obtained from Boc-Abz-Pro-NH₂, Boc-Abz-Pro-OH, as well as from various other Boc-Abz-Pro-X derivatives, after treatment with HCl or TFA under anhydrous conditions. We verified that, as recently reported, even under these synthetic conditions, deprotection of Boc-Abz-Pro-NH₂ or Boc-Abz-Pro-OH leads to the formation of the same product: pyrrolobenzodiazepine-5,11-dione. However, the formation of this compound was not detected with Abz-Pro-N(CH₃)₂, Abz-Pro-Leu-Gly-NH₂ or Abz-pyrrolidine. For all these compounds we observed an unusual behavior for the fluorescence quantum yield of Abz that can be explained as the consequence of a non-radiative deactivation process produced, specifically, by the amidation of the Abz carboxyl group with proline or a similar secondary amine such as pyrrolidine. In conclusion, these results indicate that Abz cannot be used as an internal fluorescence marker for proteolytic enzyme activity when bound directly to proline.     

Tetrapeptide substrates for the discrimination among kallikreins and other trypsin-like serine proteinases

The three tetrapeptides Ac-Phe-Arg-Arg-Val-NH2 (I), Ac-Phe-Arg-Arg-Pro-NH2 (II) and Ac-Phe-Lys-Arg-Val-NH2 (III) were shown to form a most convenient substrate system for the discrimination of the serine proteinases listed below. Tissue kallikreins (porcine pancreatic, horse and human urinary) have the unique feature of cleaving well the Arg-Arg bond in peptide I (P'2 = Val), hardly splitting it in peptide II (P'2 = Pro). The kcat/Km for the hydrolysis of peptide II by horse urinary kallikrein was 600-fold lower than that for peptide I. Trypsin, plasma kallikreins (human and rat), tonin and rat urinary kallikrein were distinguished from each other by the sequence of the N-terminal fragments formed in the hydrolysis of peptides I and/or II. Differences in the cleavage sites in these peptides are explained by differences in the specificities of the proteinase subsite S2 and/or in their preference for Arg or Lys residues. The three tetrapeptides were not substrates for plasmin.     

Synthesis of human angiotensinogen (1-17) containing one of the putative glycosylation binding sites and its hydrolysis by human renin and porcine pepsin.

The N-terminal heptadecapeptide of human angiotensinogen (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Asn-Glu-Ser-Thr-NH2 ), with the C-terminal carboxyl group amidated, was synthesized in order to study the role of Asn-Glu-Ser, a putative carbohydrate binding site, on the hydrolysis by human renin. The synthesis was performed by fragment condensation using the Honzl and Rudinger azide procedure. In our conditions for azide segment condensation, histidine racemization was demonstrated to be negligible for most of the condensation reactions. Human renin liberates angiotensin I from h-angiotensinogen (1-17)-NH2 with a Km value of 3.4 x 10(-5) M, at pH 7.3 and 37 degrees being similar to h-angiotensinogen (1-13), an analog without the carbohydrate binding site. However, the Vmax value of 4.1 x 10(-9) mol/G.U. min is one order of magnitude higher. Porcine pepsin was demonstrated to cleave preferentially Leu10-Val11 bond and, surprisingly, His9-Leu10 as well.     

Testing for context-dependence in a processing chain interaction among detritus-feeding aquatic insects

Abstract 1. Scirtid beetles may benefit mosquitoes Ochlerotatus triseriatus (Say) by consuming whole leaves and leaving behind fine particles required by mosquito larvae. Such interactions based on the sequential use of a resource that occurs in multiple forms are known as processing chains.
2. Models of processing chains predict that interactions can vary from commensal (0, +) to amensal (0, –), depending on how quickly resource is processed in the absence of consumers.
3. The scirtid– O. triseriatus system was used to test the prediction derived from processing chain models that, as consumer-independent processing increases, scirtids benefit mosquitoes less. Consumer-independent processing rate was manipulated by using different leaf species that vary in decay rate, or by physically crushing a single leaf type to different degrees.
4. Although scirtids increased the production of fine particles, the effects of scirtids on mosquitoes were weak and were not dependent on consumer-independent processing rate.
5. In the leaf manipulation experiment, a correlation between scirtid feeding and consumer-independent processing was detected. Numerical simulations suggest that such a correlation may eliminate shifts from commensal to amensal at equilibrium; because mosquito populations are typically not at equilibrium, however, this correlation may not be important.
6. There was evidence that mosquitoes affected scirtids negatively, which is inconsistent with the structure of processing chain interactions in models. Processing chain models need to incorporate more detail on the biology of scirtids and O. triseriatus , especially alternative mechanisms of interaction, if they are to describe scirtid– O. triseriatus dynamics accurately.     

An antibody that inhibits fibronectin-independent adhesion of fibroblasts to extracellular matrix material

Chinese hamster ovary (CHO) fibroblasts adhere to the extracellular matrix by both fibronectin-dependent and -independent mechanisms (Harper and Juliano, 1981a,b). Previous studies have suggested that a trypsin-sensitive, 265,000-dalton membrane glycoprotein (gp265) is involved in the fibronectin-independent adhesion process. Using a polyclonal antibody against soluble products obtained from trypsin-treated CHO cells, we have been able to further analyze this involvement. This antibody immunoprecipitates a trypsin-sensitive 265,000-dalton protein from detergent-solubilized cells. Incubation of AdvF11, a variant cell line that does not utilize fibronectin for adhesion, with this antibody blocks their adhesion to extracellular matrix material (ECM). The immunoglobulin fraction will also partially block adhesion of the parental cell line to ECM particularly when the ECM is first treated with an antifibronectin antibody. Taken together these results add support for the involvement of gp265 in fibronectin-independent adhesion and provide a methodology for further characterization.     

Properties of prolamin in mature and developing rice grain

A procedure was developed for preparing lipid- and phenol-free prolamin directly from IR480-5-9 milled rice (Oryza sativa L.).The preparation consisted mainly of one protein band on analytical and SDS-polyacrylamide disc gel electrophoresis with subunit MW of 17000 and a minor fraction with subunit MW 23000. The prolamin eluted as a single peak on SDS-Sephadex G-75 gel filtration and on DEAE-cellulose column chromatography. Prolamin was poor in lysine, histidine, cystine, and methionine but rich in glutamic acid, tyrosine and proline. In dehulled developing grain of two different rices, changes in the aminogram of the prolamin fraction coincided with the start of endosperm protein body synthesis and the appearance from 7 days after flowering of a second prolamin subunit with MW 23 000.