Chemical composition and ultrastructure of the epicuticular wax in four mutants of Pisum sativum (L)

The action of mutations affecting the epicuticular wax of Pisum sativum has been investigated at the chemical and ultrastructural level. Upper and lower surfaces of the leaves were found to differ markedly in both ultrastructure and chemistry. Mutations affected primarily either the lower (wa, wb and wsp) or the upper surface (wlo), but some effects of all 4 genes could be seen on both surfaces. Specific biochemical lesions could be implied for wsp and wa but the chemical effects of wb and wlo were more diffuse. Generally a close relation between chemical composition and crystallite form of the wax was evident throughout the work.     

Chemical composition and ultrastructure of the epicuticular wax in three lines of Brassica napus (L)

The epicuticular wax in three lines of Brassica napus (rape) has been investigated and the detailed chemistry and ultrastructure of the waxes examined. A distinct chemical make-up has been found for all three waxes which is correlated with three distinct crystallite structures. A tentative scheme for classification of Brassica wax mutants is described in which the two newly analysed rape mutants can be placed. Mass spectral analysis of all wax components confirms and extends previous ideas about the chemistry of Brassica waxes.     

Role of the membrane-associated folate binding protein (folate receptor) in methotrexate transport by human KB cells

The uptake of methotrexate by KB cells was observed to be dependent on time, temperature, and concentration of extracellular methotrexate. The Kd for methotrexate surface binding to KB cells was approximately 200 nM. Following exposure of KB cells to trace quantities of [3H]methotrexate for periods ranging from 6 min to 24 h, the cellular methotrexate was progressively formed into methotrexate polyglutamates and was bound to dihydrofolate reductase as well as to a particulate folate binding protein. To further study the mechanism of methotrexate uptake in KB cells, the N-hydroxysuccinimide ester of methotrexate was used to covalently label the surface of KB cells and to inhibit transport of methotrexate. The N-hydroxysuccinimide ester of methotrexate was bound to a species of protein with an apparent molecular weight of 160,000 in 1% (v/v) Triton X-100 that bound folic acid and was specifically precipitated by antiserum raised against the previously purified high-affinity folate binding protein (the folate receptor) from human KB cells. In addition, trypsin was utilized to remove surface-accessible covalently bound methotrexate. The amount of covalently bound methotrexate that could be released by trypsin initially decreased on incubation at 37 degrees C, suggesting that the methotrexate and binding protein were internalized. However, with time, trypsin could again release the covalently bound methotrexate, suggesting that the binding protein cycles from the external cell surface to the inside of the cell and out again.     

Transport of hydrophobic ions in erythrocyte membrane: I. Zero membrane potential properties

Summary The permeability and partition coefficients of tetraphenylarsonium (TPA) and several other organic cations were studied in the human erythrocyte using an ion-selective electrode. The permeability constant for the different cations could be explained quite well by differences in oil/water partition coefficients. No evidence for facilitated transport could be found. Binding of the organic ions occurred to both the cell membrane and to intracellular contents. Partitioning to the membrane remained relatively constant despite variation from ion intracellular binding with blood samples from different donors. TPA flux is stimulated by substoichiometric amounts of tetraphenylboron and other organic anions, suggesting an ion-pairing mechanism.     

The N-Shaped Current-Potential Characteristic in Frog Skin: III. Ionic Dependence

A ramp voltage clamp measurement described previously is used to detect alterations in the frog skin current-potential (I-V) characteristic following removal or replacement of various ions in the solutions bathing the skin. The ionic requirements for the maintenance of a negative-slope I-V property are the following: Ca⁺⁺, Na⁺, and Cl^- must be in the outside solution; K⁺ and Cl^- must be in the inside solution. Removal of any one of these ions from its respective solution results in the decay and eventual disappearance of the negative slope.

The similarity between the I-V characteristic following Ca⁺⁺ removal with EDTA from the outside solution and the I-V relation in a refractory skin suggests that the loss (refractory state) and recovery of the negative slope is a consequence of unbinding and subsequent rebinding of Ca⁺⁺ to membrane sites. The role of the univalent ions is not clear—presumably some or all of these ions constitute the current through the skin; however, some of these ions may also be involved in maintaining a membrane condition necessary for the existence of a negative slope I-V relation. Further, excitation does not appear to be a direct consequence of the Na⁺ pump.

     

The N-Shaped Current-Potential Characteristic in Frog Skin: II. Kinetic Behavior during Ramp Voltage Clamp

Previous step voltage-clamp measurements on frog skin showed the presence of an N-shaped current-potential (I-V) relation in excitable skin. However, the collection and reconstruction of I-V data using discrete step changes of skin potential was tedious because of the long refractory period (up to 1 min) in frog skin. A direct and rapid (5 msec) method for recording the N-shaped I-V characteristic in real time is presented. Ramp functions are used as the command to the clamp system instead of a step function. Consequently the skin potential is forced to change in a linear manner (as commanded) and the skin current can be recorded as a continuous function of the controlled change of skin potential. With the ramp clamp, a low-resistance membrane state ( 10 Omega . cm(2)) resembling a breakdown phenomenon was observed at high skin potential ( 300 mv). Entry into the low resistance state resulted in a collapse of the N-shaped I-V relation to a nearly linear function. The utility of the ramp measurement is demonstrated by predicting (1) that the maximum rate of rise of the spike occurs at a voltage corresponding to the valley (local minimum) in the N-shaped I-V curve, (2) that the rate of rise of the spike increases with increasing clamp currents, (3) the voltage peak of the spike, and (4) the time course of the rising phase of the spike.     

Fat Metabolism in Higher Plants XXXVI: Long Chain Fatty Acid Synthesis in Germinating Peas

A low lipid, high starch containing tissue, namely cotyledons of germinating pea seedlings was examined for its capacity to synthesize fatty acid. Intact tissue slices readily incorporate acetate-¹⁴C into fatty acids from C₁₆ to C₂₄. Although crude homogenates synthesize primarily 16:0 and 18:0 from malonyl CoA, subsequent fractionation into a 10,000g pellet, a 10⁵g pellet and supernatant (soluble synthetase) revealed that the 10⁵g pellet readily synthesizes C₁₆ to C₂₈ fatty acids whereas the 10,000g and the supernatant synthesize primarily C₁₆ and C₁₈. All systems require acyl carrier protein (ACP), TPNH, DPNH if malonyl CoA is the substrate and ACP, Mg²⁺, CO₂, ATP, TPNH, and DPNH if acetyl CoA is the substrate. The cotyledons of germinating pea seedlings appear to have a soluble synthetase and 10,000g particles for the synthesis of C₁₆ and C₁₈ fatty acid, and 10⁵g particles which specifically synthesize the very long chain fatty acid from malonyl CoA, presumably via malonyl ACP.     

A quasi-steady-state approximation method for diffusion problems: I. Concentration dependent diffusion coefficients

A generalization of Landahl's approximation method (H. D. Landahl,Bull. Math. Biophysics,15, 49–61, 1953) for non-linear diffusion problems is suggested. The method is applied to sorption, desorption, and free diffusion problems involving concentration-dependent diffusion coefficients. With some limitations, the results compare favorably with those obtained by numerical methods.     

mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species

Reconstructions of the human-African great ape phylogeny by using mitochondrial DNA (mtDNA) have been subject to considerable debate. One confounding factor may be the lack of data on intraspecific variation. To test this hypothesis, we examined the effect of intraspecific mtDNA diversity on the phylogenetic reconstruction of another Plio- Pleistocene radiation of higher primates, the fascicularis group of macaque (Macaca) monkey species. Fifteen endonucleases were used to identify 10 haplotypes of 40-47 restriction sites in M. mulatta, which were compared with similar data for the other members of this species group. Interpopulational, intraspecific mtDNA diversity was large (0.5%- 4.5%), and estimates of divergence time and branching order incorporating this variation were substantially different from those based on single representatives of each species. We conclude that intraspecific mtDNA diversity is substantial in at least some primate species. Consequently, without prior information on the extent of genetic diversity within a particular species, intraspecific variation must be assessed and accounted for when reconstructing primate phylogenies. Further, we question the reliability of hominoid mtDNA phylogenies, based as they are on one or a few representatives of each species, in an already depauperate superfamily of primates.      

The excitation of the heart and its modification under the influence of the chemical mediators and the cardiac nerves: II. A particular case of the one-factor theory

Previous work (Macey, 1952) in the application of the one-factor theory to the heart is extended. The rate of production of the excitatory state is assumed to be linear. Two possible mechanisms are indicated whereby such a situation might arise. Assumptions are made regarding the mode of action of the chemical mediators on the heart, and an equation is derived relating the heart rate to the frequency of nerve impulses traveling along the cardiac nerves. This result compares favorably with the experimental findings of A. Rosenblueth and F. A. Simeone (1934). Other experimental results are interpreted in terms of the theory. United States Public Health Service Fellow in Mathematical Biology.