The adenosine-triphosphatase activity of adrenal chromaffin granules

1. The preparation of a fraction containing highly purified chromaffin granules from the bovine adrenal medulla is described. 2. The fraction contains an adenosine-triphosphatase activity that is stimulated by Mg²⁺ and that cannot be explained by contamination with mitochondria or microsomes. 3. It is suggested that the adenosine-triphosphatase activity is related to the uptake of cate-cholamines by the chromaffin granules.     

The biological and immunological properties of fractionated atrial extracts from young and old rats

We have previously reported that the biological activity of rat atrial extract declines with age. The present study was undertaken to further evaluate the natriuretic, hypotensive and immunological properties of fractionated and HPLC purified atrial extracts prepared from young and old rats. Acetic acid extracts were prepared and subsequently fractionated by gel permeation chromatography. The high (greater than 10,000 daltons) and low (less than or equal to 10,000 daltons) molecular weight fractions were collected, lyophilized and assayed. Radioimmunoassay competitive binding curves of the initial and fractionated extracts were parallel (p greater than 0.05) to the synthetic ANP standard. No differences in parallelism (p greater than 0.05) were observed in the natriuretic activity of the initial extracts, the low molecular weight (LMW) fractions from both age groups, the 290 day high molecular weight (HMW) fraction or the synthetic ANP standard. However, the natriuretic activity of the 15 day HMW fraction was significantly attenuated compared to the other treatment groups (p less than 0.05). The initial 15 day extract was also significantly more hypotensive than the 290 day extract (p less than 0.05). HMW extracts were subjected to HPLC and the resulting immunoreactive ANP peak was reassayed. Based on SDS-PAGE and immuno blot analysis, the HPLC purified fraction was found to contain only immunoreactive proANP. Subsequent bioassay revealed greater hypotension and reduced natriuretic activity in the 15 day proANP fraction in comparison to a similarly prepared extract from older animals. Thus, we conclude that qualitative differences in the biological properties of atrial extracts may be ascribable to age-related changes in the composition of proANP or to other undefined biologically active atrial substance(s).     

Perceptual constraints on optimal foraging: The effects of variation among foragers

Summary We present a simple model of habitat selection in which individuals differ in their ability to discriminate between resource sites' profitabilities. The model investigates the effects of violating the ideal assumption of the well-known ideal free distribution (IFD). We show that (1) variability in perceptual limits within a population can significantly change the distribution of foraging animals even though the mean perceptual limit is the same, (2) the direction of this change depends on the proportion of the population that choose randomly between resource sites and (3) better perceivers are more likely to be found at individually more profitable sites, which, because of undermatching with respect to the IFD, are also the absolutely more profitable sites. We note that variability in perceptual limits almost always led to an undermatching of organisms to resources, thereby extending previous workers' results implying that the incorporation of any form of perceptual limits leads to undermatching with respect to the IFD.     

Anaerobic digestion of palm oil mill effluent and condensation water waste: an overall kinetic model for methane production and substrate utilization

The process of anaerobic digestion is viewed as a series of reactions which can be described kinetically both in terms of substrate utilization and methane production. It is considered that the rate limiting factor in the digestion of complex wastewaters is hydrolysis and this cannot be adequately described using a Monod equation. In contrast readily assimilable wastewaters conform well to this approach. A generalized equation has thus been derived, based on both the Monod and Contois equations, which serves extreme cases. The model was verified experimentally using continuous feed anaerobic digesters treating palm oil mill effluent (POME) and condensation water from a thermal concentration process. POME represents a complex substrate comprising of unhydrolyzed materials whereas the condensation water is predominantly short chain volatile fatty acids. Substrate removal and methane production in both cases could be predicted accurately using the generalized equation presented.List of Symbols A (=K_skY/K_h) Kinetic parameter - B Specific methane yield, 1 of CH₄/g of substrate added B₀ Maximum specific methane yield, 1 of CH₄/g of substrate added at infinity - C Empirical constant in Contois equation - F Volumetric substrate removal rate, g/l day - k Hydrolysed substrate transport rate coefficient, 1/days - K (=YC) Kinetic parameter in Chen-Hashimoto equation - K _h Substrate hydrolysis rate coefficient, 1/days - K _s Half-saturation constant for hydrolysed substrate, g/l - M _v Volumetric methane production rate, 1 of CH₄/l day - MS Mineral solids, g/l - MSS Mineral suspended soilds, g/l - POME Palm oil mill effluent - R (=S_r/S_T0) Refractory coefficient - S _h Concentration of hydrolysed substrate, g/l - S _u Intracellular concentration of hydrolysed substrate, g/l - S ₀ Input biodegradable substrate concentration, g/l - S Biodegradable substrate concentration in the effluent or in the digester, g/l - S _r Refractory feed substrate concentration, g/l - S _T0 (=S₀+S_r) Total feed substrate concentration, g/l - S _T (S+S_r) Total substrate concentration in the effluent, g/l - TS Total solids, g/l - TSS Total suspended solids, g/l - VFA Total volatile fatty acids, g/l - VS Volatile solids, g/l - VSS Volatile suspended solids, g/l - X Biomass concentration, g/l - Y Biomass yield coefficient, biomass/substrate mass - Hydraulic retention time, days. - Specific growth rate of microorganisms, l/days - _m Maximum specific growth rate of microorganisms, l/days The authors wish to express their gratitude to the Departamento de Postgrado y Especialización del CSIC and to the Consejería de Educación y Ciencia de la Junta de Andalucia for their financial support of this work.     

1.56 Å structure of mature truncated human fibroblast collagenase

The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc.     

Semicontinuous anaerobic digestion of soft drink wastewater in immobilised cell bioreactors

Summary Saponite support considerably increased the kinetics of a. semicontinuous anaerobic digestion process treating soft drink wastewater showing values of the _max andK kinetic parameters (Chen and Hashimoto model) 2.5 and 1.4 times higher than for bentonite and polyurethane support, respectively. This was significant at 95% confidence level.     

Recognition by and in vitro induction of cytotoxic T lymphocytes against predicted epitopes of the immediate-early protein ICP27 of herpes simplex virus.

The identification of herpes simplex virus type 1 (HSV-1) proteins and the minimal epitopes within these proteins which serve as targets for cytotoxic T lymphocytes (CTL) remains an important goal for the development of effective vaccine strategies. In this report, an H-2Kd allele-specific peptide-binding motif was used to locate putative CTL epitopes in the HSV-1 immediate-early protein ICP27, a protein previously identified as a major CTL target in the BALB/c mouse. Peptides 1 (amino acids 322 to 332) and 2 (amino acids 448 to 456) synthesized to represent two separate predicted CTL epitopes in ICP27 were able to sensitize target cells in vitro for recognition by HSV-1-specific CTL. Moreover, using a recently developed system to generate primary CTL responses in vitro, both peptides induced primary CTL which reacted with target cells expressing HSV-1. This system allowed us to verify the activity of two CTL epitopes in the ICP27 protein and holds promise as a rapid way of identifying immunogenic peptides from any protein molecule.     

Calcium-independent activation of skeletal muscle fibers by a modified form of cardiac troponin C.

A conformational change accompanying Ca2+ binding to troponin C (TnC) constitutes the initial event in contractile regulation of vertebrate striated muscle. We replaced endogenous TnC in single skinned fibers from rabbit psoas muscle with a modified form of cardiac TnC (cTnC) which, unlike native cTnC, probably contains an intramolecular disulfide bond. We found that such activating TnC (aTnC) enables force generation and shortening in the absence of calcium. With aTnC, both force and shortening velocity were the same at pCa 9.2 and pCa 4.0. aTnc could not be extracted under conditions which resulted in extraction of endogenous TnC. Thus, aTnC provides a stable model for structural studies of a calcium binding protein in the active conformation as well as a useful tool for physiological studies on the primary and secondary effects of Ca2+ on the molecular kinetics of muscle contraction.