Chitin synthetase ofNeurospora crassa: Inhibition by nikkomycin,polyoxin B,and UDP

The inhibitory effects of nikkomycin, polyoxin B, and UDP were tested on particulate chitin synthetase activity (UDP-2-acetamido-2-deoxy-D-glucose: chitin-4-B-acetamidodeoxy-D-glucosyltransferase, E.C.2.4.1.16) fromNeurospora crassa. Two approaches were used: (a) inhibitors were tested for their individual effects on chitin synthetase activity; (b) paired combinations of inhibitors were examined to establish whether the compounds affected inhibition by binding at the same enzyme site. The first method showed that the three compounds are linear competitive inhibitors, i.e. each competes directly with the substrate for binding. K_{i app} values were: UDP, 0.8 mM; polyoxin B, 32 M; and nikkomycin, 2 M. The second method showed that the inhibitors compete with each other for binding; thus they bind at the same site. The pyrimidine nucleoside moiety of these inhibitors is an essential component for effective inhibition, but the potency of inhibition is critically dependent on the conformation of the side group attached to carbon 5 of the ribose sugar.     

The endocytosis of concanavalin A by Dictyostelium discoideum cells

Differentiating cells of D. discoideum in suspension bind ConA. The proportion of the bound lectin which is competitively removed by methyl-α- mannopyranoside decreases with the time of exposure. Ferritin conjugated ConA is seen to bind both to the cell surface and to be taken into the cells, the proportion of the ConA inside the cells increasing with time. The surface bound ConA is removed by washing with methyl-α- mannopyranoside while the endocytosed ConA appears unaffected. It is suggested that much of the [¹²⁵I]ConA, uncompetable by methyl-α- mannopyranoside in our and other binding studies, may be this intracellular ConA.     

Methionine Sulfoximine Effects on C4 Plant Leaf Discs: Comparison with C3 Species

Methionine sulfoximine caused ammonia accumulation and photosyntheticrate inhibition in leaf discs from two C₄ species, Zea maysL. cv. F. M. Cross (Hybrid) and Sorghum bicolor L. Moench cv.NC-70X, as well as one C₃ plant species, Datura stramonium L.cv. stramonium. Similar results were obtained earlier with theC₃ species Spinacia oleracea L. The effect occurred in the absenceof inorganic nitrogen reduction and was light dependent. Ammoniaaccumulation rates were similar in all four species examined.The results support a role for glutamine synthetase in leafammonia recycling in both C₄ and C₃ leaves. ¹ Current address: Cetus Madison Corporation, 2208 Parview Road,Middleton, WI 53562, U.S.A. (Received November 2, 1981; Accepted April 28, 1982)     

Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity

Cogley T. P., Anderson J. R. and Cooley L. J. 1982. Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity. International Journal for Parasitology12: 473–480. Larvae of G. intestinalis pursued a specific migratory pathway within the equine oral cavity en route to the stomach. The larval migration included the following sequence: burrowing in the tongue mucosa, invasion of the interdental spaces, transitory attachment at the root of the tongue and movement to the stomach. The molt from first to second instar did not occur in the tongue, as commonly believed, but between the interdental spaces. Ninety five percent of the larvae invading the interdental spaces were associated with gingiva of the upper molars. SEM analysis revealed further details of the oral migration: (1) air holes excavated in the epithelium which connect with deeper burrows; (2) an intimate association between air holes and posterior spiracles of larvae; (3) precise impressions of larvae in tissue immediately surrounding the most recently formed burrows; and (4) initial larval entry into the tongue through the use of natural disruptions or healing lesions. Factors influencing the development of the oral migration are discussed.     

Effects of anesthetic alcohols on membrane transport processes in human erythrocytes

1. 1. Anesthetic alcohols (pentanol, hexanol and heptanol) were found to increase the fluidity of red cell membrane lipids as monitored by the fluorescence depolarization of diphenylhexatriene. The relative potency of the alcohols was found to be parallel to their relative membrane/water partition coefficients.

2. 2. Hexanol had biphasic effect on erythritol uptake by simple diffusion by red cells. At concentrations less than 9 mM, hexanol had no significant effect. At concentrations greater than 9 mM, there was an approximately linear increase in erythritol permeability with increasing alcohol concentration.

3. 3. The facilitated transport of uridine was markedly inhibited by hexanol. Hexanol at 6 mM produced a 65% inhibition of uridine (4 mM) uptake. Hexanol decreased both the apparent K_m and V values for the equilibrium exchange of uridine.

4. 4. The facilitated transport of galactose was only slightly inhibited by hexanol.

5. 5. Hexanol was without effect on the passive and active fluxes of Na⁺ and K⁺ in red cells with altered cation contents. Cells that were slightly depleted of K⁺ and cells that were highly K⁺-depleted were both insensitive to hexanol.

(p-Amidinophenyl)methanesulfonyl fluoride, an irreversible inhibitor of serine proteases

p-(Amidinophenyl)methanesulfonyl fluoride (p-APMSF) has been synthesized and shown to be a specific, irreversible inhibitor of the class of plasma serine proteases which demonstrate substrate specificity for the positively charged side chains of the amino acid lysine or arginine. In equimolar concentration, this compound causes immediate and complete irreversible inhibition of bovine trypsin and human thrombin. A 5-10-fold molar excess of reagent over enzyme is required to achieve complete irreversible inhibition of bovine Factor Xa, human plasmin, human C1-r, and human C1-s. the Ki of p-APMSF for all of the above-mentioned proteases is between 1 and 2 microM. In contrast, p-APMSF in large molar excess does not inactivate chymotrypsin or acetylcholinesterase. The unique reactivity of p-APMSF has been further shown in comparison with the related compound p-nitrophenyl (p-amidinophenyl)methanesulfonate which is an active-site titrant for thrombin but reacts poorly with Factor Xa, C1-r, and C1-s and is not hydrolyzed by bovine trypsin or human plasmin. Similarly, (p-amidinophenyl)methanesulfonate has a Ki of 30 microM for thrombin but is a poor inhibitor of trypsin, Factor Xa, C1-r, C1-s, and plasmin. Studies with bovine trypsin have demonstrated that the inhibitory activity of p-APMSF is the result of its interaction with the diisopropyl fluorophosphate reactive site. The unique reactivity of this inhibitor classifies it as one of the most effective active site directed reagents for this class of serine proteases. Collectively, these results suggest that the primary substrate binding site of these enzymes, which share a high degree of structural homology, do in fact significantly differ from each other in their ability to interact with low molecular weight inhibitors and synthetic substrates.     

Two isoaccepting seryl tRNAs coded by separate mitochondrial genes in yeast

Summary In S. cerevisiae four isoacceptor mitochondrial tRNAs for serine have been separated by reversed phase chromatography. At least two of these species are products of different genes. In this work the deletion mapping technique has been used to locate two genes for tRNA^ser. The gene for tRNA^ser previously localized in the oli I region of the mitochondrial genome has been found to code for tRNA _ser ² , and another gene coding for tRNA _ser ¹ has been detected in the region where most of other tRNA genes are found. Results of fine mapping experiments allowed to localize this gene in the proximity of the gene for tRNA^arg.     

Water utilization of tropical hardwood hammocks of the Lower Florida Keys

Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.