The potency of tissue-type plasminogen activator (TPA) determined with chromogen and clot-lysis assays

An assessment was made of two methods for determining the potency of tissue-type plasminogen activator (TPA). A chromogenic microtitre plate assay was established which contained TPA, plasminogen, a synthetic plasmin substrate (H-D-valyl-L-leucyl-L-lysyl-p-nitroaniline dihydrochloride, S2251) and any one of the following stimulators: native fibrinogen, enzymatic and chemical digests of fibrinogen, poly-D-lysine (PDL) and chemical derivatives of the latter. The chromogen assay was compared with an automated clot-lysis (turbidimetric) assay for sensitivity, reproducibility and validity for potency determination. Reference preparations of TPA were titrated in both assays: in the chromogen assay the dose-response curves were non-parallel, whereas parallelism was observed in the clot-lysis assay. Thus, the chromogen assay was restricted in its applicability and disqualified from any routine regulatory use. The potency of individual lots of recombinant (r)TPA could only be estimated in International Units (IU) of TPA activity with the automated clot-lysis assay and the potency values obtained (IU/vial) were in remarkably close agreement with the manufacturers' values.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

A numerical model for the oxygenation of blood in lung capillaries--effect of nth order one-step kinetics of oxygen uptake by haemoglobin

A numerical model is described for the oxygenation of blood in lung capillaries by considering the transport mechanisms of molecular diffusion, convection and the facilitated diffusion due to the presence of haemoglobin. In order to represent the oxygen dissociation curve accurately in the model, the nth order one-step kinetics of oxygen uptake by haemoglobin has been used. The resulting system of coupled, non-linear partial differential equations is solved numerically. It is shown that the blood is required to traverse a larger distance in the capillary before becoming fully oxygenated with nth order one-step kinetics in comparison to first-order one-step kinetics.     

A preliminary analysis of distribution patterns in a large, pantropical genus, Barleria L. (Acanthaceae)

Barleria L. (Acanthaceae) is a large, polymorphic, widespread genus of herbs and shrubs comprising about 300 species, occurring mainly in Africa and Asia but with one species, Barleria oenotheroides Dum.Cours., extending to the New World tropics. Recent completion of a monographic infra-generic classification of the genus (in which seven sections are recognised, and the names of four of these validated in this paper—see Appendix 1), has facilitated a comprehensive analysis of distribution patterns on a global scale. The richest representation of Barleria is in Africa where there are two centres of diversity, one in tropical East Africa (about eighty species) and the other in southern Africa (about seventy species). The number of species tails off rapidly to both the Far East and the West. Barleria shows a marked trans-Atlantic disjunction between West Africa and the Neotropics, with B. oenotheroides shared by these two regions. This type of disjunction, which is known in other genera of the family, cannot be adequately explained in Barleria on the basis of long-distance dispersal or past continental movements. There is a high degree of regional endemism (e.g. 75% for the Indian subcontinent) at both the species and sectional levels within this genus. The degree of similarity between regions is correspondingly low. The endemics in each region tend to belong to only one or a few of the sections. There are few truly widespread taxa within the genus. East and West Africa are the only regions in which all sections are represented. Sections Barleria and Prionitis C.B. Cl. are the most widespread in the genus; Sections Somalia (Oliv.) Lindau, Fissimura M. Balkwill and Stellatohirtae M. Balkwill are mainly restricted to Africa and Sections Chrysothrix M. Balkwill and Cavirostrata M. Balkwill are the most restricted, occurring mainly in India and Sri Lanka. On a local scale, many of the species show highly restricted, clumped distributions; this is apparently related to particular soil types and possibly to the short-distance, ballistic mode of seed dispersal. This account of the biogeography of Barleria is to be regarded as preliminary, as much taxonomic work at the species level remains to be done before a full-scale cladistic biogeographic account can be undertaken. Particular areas worthy of future investigation include establishing the centre of origin of the genus and investigating the basis for the high degree of endemism shown by many of the species.     

The effect of growth conditions on adenylate cyclase activity and virulence-related properties of Bordetella pertussis

Growth of Bordetella pertussis in Stainer & Scholte medium in which the NaCl had been replaced by one of several inorganic or organic salts resulted in a large decrease in adenylate cyclase activity, histamine-sensitizing activity and in the amounts of two cell-envelope polypeptides of Mr 28000 and 30000. Although some variation between strains was observed, there was never a case where one of these properties was lost independently of the others. Cultures in which these properties were lost had decreased amounts of extracellular cAMP when compared to NaCl-grown cultures. Adenylate cyclase activity was detected in three locations of B. pertussis cultures (extracellular, extracytoplasmic but cell-associated, and cytoplasmic). After growth in medium containing high concentrations of MgSO4, enzyme activity was decreased to a similar extent in all three locations.     

Phospholipid turnover during cell-cycle traverse in synchronous Chinese-hamster ovary cells. Mitogenesis without phosphoinositide breakdown.

The turnover of phospholipids was investigated in quiescent serum-starved Chinese-hamster ovary (CHO-K1) cells stimulated to progress through the cell cycle by the addition of dialysed bovine serum. A variety of radiolabelling techniques were employed to study the rapid effects of serum on phospholipids and later events during G1 and S phases of the cell cycle. Pulse-labelling studies using [32P]Pi revealed that there was a stimulation of the synthesis rate of all phospholipids investigated during the initial few hours after serum addition. The greatest stimulation (20-fold) was observed in phosphatidylcholine, and the smallest in the polyphosphoinositides (PPIs). Mock stimulation with serum-free medium caused a similar increase in PPI turnover, but little or no effect on turnover of other phospholipids. This effect could be accounted for by a stimulation of the turnover of cellular ATP pools increasing [32P]ATP specific radioactivity. Late G1 and S phases were associated with a decrease in the rate of synthesis of all phospholipids. Phosphatidic acid was the only phospholipid whose labelling fell below that in mock-stimulated cells during the period of the cell cycle. Stimulation of serum-starved cells that had been prelabelled with myo-[2-3H]inositol caused no change in the amounts of inositol trisphosphate, but both serum-stimulated and mock-stimulated cells exhibited similar small decreases in both inositol bisphosphate and inositol monophosphate, of approx. 30% after 30 s. When cells were serum-stimulated in the presence of 10 mM-Li+, there was no increase in the size of the total inositol phosphate pool. We conclude that mitogenic stimulation and cell-cycle traverse cause profound and complex effects on phospholipid turnover in CHO-K1 cells, but there is no evidence for a role of inositol lipid turnover in the proliferative response to serum in this cell line.