Foundations of the use of an enzyme-kinetic analogy in cell-mediated cytotoxicity

A mathematical model of the ⁵¹Cr-release microcytotoxicity assay is utilized to find conditions under which the kinetics of this assay resemble the kinetics of a classical enzyme-substrate reaction. Assuming a steady-state approximation, that “bystander” effector cells do not bind markedly better than the cytotoxic effector cells, and that the programming of the target cells for lysis is irreversible, it is shown that the velocity of label release is v = v_maxT_T/(K_{$\text{1}\text{2}$}+T_T), where both V_max and K_{$\text{1}\text{2}$} are linear functions of the effector-cell population and T_T is the initial target-cell population. Moreover, the expressions for K_{$\text{1}\text{2}$} and V_max are expressed in terms of natural kinetic parameters of the process and attributes of the noncytotoxic bystanders.     

Susceptibility of Legionella pneumophila to Ultraviolet Radiation

Distilled water suspensions of Legionella pneumophila were found to be sensitive to low doses of germicidal ultraviolet radiation.     

A spectroscopic study of metal ion and ligand binding to β-lactamase II

β-Lactamase II has two metal-binding sites. The electronic spectra of Cd(II)- and Co(II)-substituted β-lactamase II have been investigated. It is suggested that a thiol ligand is involved in metal binding at the first site. The stoichiometric dissociation constants for Co(II) binding to β-lactamase II were estimated to be 0.13 and 2.66 mM (pH 6.0, 4°C, 1 M NaCl) by equilibrium dialysis. Competition between Zn(II) and Co(II) for the first metal binding site suggests a value of 0.7 μM (pH 6.0, 30°C, 1 M NaCl) for the dissociation constant o Zn(II).The electronic spectra of the Co(II) enzyme lead to the suggestion that the coordination geometries around the metal ions in the first and second sites are related to those of a distorted tetrahedron and octahedron, respectively.     

The influence of zooplankton food resources on the morphology of the estuarine clupeid Gilchristella aestuarius (Gilchrist, 1914)

Synopsis The body shape of the estuarine clupeidGilchristella aestuarius from the St. Lucia system is different from that of the same species in other estuaries. The morphology ofG. aestuarius is discussed in relation to long term food availability in the St. Lucia system.     

The stylet apparatus of the nemertean Paranemertes Peregrina: Its ultrastructure and role in prey capture

Summary The nemertean Paranemertes peregrina captures prey by using an eversible proboscis that is armed with a stylet apparatus. The apparatus consists of several reserve stylet sacs and a central stylet that is attached to a granular mass, called the basis. When the proboscis is everted, the central stylet is used to stab prey such as nereid polychaetes, and paralytic neurotoxins, produced in the proboscis, are inserted in the stylet-induced wounds. The central stylet averages 85 m in length and has helically-arranged grooves along its shaft. The proximal piece of the central stylet is anchored to the basis, apparently by adhesive granules in the anterior end of the basis. A basis sheath surrounds the basis and is continuous posteriorly with a duct, called the ductus ejaculatorius. Secretions in the ductus ejaculatorius may contain some of the toxin that is used to immobilize the prey. The contents of the duct are probably injected into the prey by way of the grooves on the central stylet. In the region anterior to the central stylet, there are numerous glandular cells and anchor cells that are believed to attach the stylet apparatus to the prey during attack. Each reserve stylet sac is lined by a simple epithelium. One of the epithelial cells, called the styletocyte, is greatly enlarged and fills the lumen of the sac. Several reserve stylets are assembled in a styletocyte. Each reserve stylet is formed within a membrane-bound vacuole associated with the Golgi apparatus and is composed of an inner organic core surrounded by an inorganic cortex. A duct connects each reserve stylet sac with the area around the central stylet and provides a pathway for the transfer of reserve stylets during replacement of the central stylet.     

Scanning electron microscopic study of spermatozoa from gossypol-treated rats

Summary Spermatozoa from the cauda epididymidis of gossypol-treated rats exhibit distinctive departures from the morphology of spermatozoa from control rats: wrinkled and disorganized cell membrane in the head and tail regions, cell membrane missing from segments of the tail midpiece and principal piece regions, malformed heads, decapitate spermatozoa, retention of a cytoplasmic droplet at variable loci along tail midpieces, and looped tails. The observations suggest that gossypol exerts its contraceptive effect during spermatocytogenesis and spermiogenesis, including the posttesticular development and maturation of spermatozoa in the epididymis.     

Chemical induction of β-carotene biosynthesis

Marsh white seedless grapefruit were treated with the 2-diethylaminoethanol esters of the following acids: benzoic, phenylacetic, hydrocinnamic, 4-phenylbutyric, 5-phenylvaleric, valeric, hexanoic, heptanoic, octanoic, nonanoic, 5-chlorovaleric, cyclohexanecarboxylic, phenoxyacetic, p-chlorophenoxyacetic, 3-phenoxypropionic, cinnamic and p-chlorocinnamic. Several of these esters, in particular the hexanoate, 4-phenylbutyrate and cinnamate, caused the accumulation of large amounts of β-carotene. The effects of the hexanoate and of 2-phenoxytriethylamine, which causes only lycopene accumulation, were studied as functions of time. The hexanoate caused the rapid accumulation of lycopene during the first day. The amount of lycopene then began to decrease and that of β-carotene increased until, after 14 days, β-carotene was the major pigment. 2-Phenoxytriethylamine caused rapid lycopene accumulation during the first day and a slow steady increase afterwards. Thus, the mode of action of the β-carotene inducers may be similar to that of the lycopene inducers except that the former are probably rapidly hydrolysed by the esterase(s) in the flavedo, so that they no longer inhibit the cyclase(s), and β-carotene is accumulated at the expanse of lycopene.     

Effects of insecticides on acetylene reduction by Azotobacter vinelandii and soybean nodules

Summary Nine organophosphate and carbamate insecticides were tested for effects on ability of Azotobacter vinelandii to reduce acetylene. Only Gardona^R, at higher concentrations, was significantly inhibitory. The same pesticides were tested with soybeans (Glycine max L.). Some minor phytotoxic effects were noted, but there was no inhibition of the ability of the excised nodules of the plants to reduce acetylene.Published with the approval of the Director of the North Dakota Agricultural Experiment Station as Journal Article No. 726. Portion of a thesis presented by the senior author in partial fulfillment of the requirements for the M.S. degree in bacteriology at North Dakota State University.Published with the approval of the Director of the North Dakota Agricultural Experiment Station as Journal Article No. 726. Portion of a thesis presented by the senior author in partial fulfillment of the requirements for the M.S. degree in bacteriology at North Dakota State University.     

Interaction of methotrexate with polycationic carriers

Binding parameters were measured for the $\text{in vitro}$ interaction of methotrexate with poly-L-lysine and diethylaminoethyl dextran. The complexes were found to have apparent affinity constants of 2590 and 440 M^?1 respectively at 37°, ionic strength 0.02. For hypotonic solutions containing therapeutic concentrations of methotrexate, this results in 87% binding of the drug to poly-L-lysine and 74% to diethylaminoethyl dextran. While the binding decreased to about 50% upon increasing ionic strength to physiologic levels, sufficient drug-carrying capacity was retained at isotonicity to support the potential utility of such complexes as tissue-specific drug carriers.