Asymmetric labeling of amino lipids in liposomes.

Fluorescamine and trinitrobenzenesulfonate were used as chemical probes to differentially label amino phospholipids in liposomes. At low concentrations, fluorescamine reacts primarily with amino lipids on the external half of the bilayer. Further increase in fluorescamine concentration resulted in a linear increase of labeling indicating penetration and reaction with the internal half of the bilayer. Because of the pH requirements of the fluorescamine reaction, internal labeling was eliminated with a H+ gradient: inside acidic/outside alkaline. Differential labeling was also achieved with trinitrobenzenesulfonate, which is normally not permeable but which can be transported by valinomycin-K+ complex and react with internal amines. Thus, either half of the bilayer can be labeled with the same or different reagents. When liposomes were double-labeled, the fluorescence of fluorescamine was quenched by the trinitrobenzenesulfonate label. This quenching was reversed by solubilizing the liposomes with acidic ethanol. No quenching occurred when fluorescamine-labeled liposomes were mixed with trinitrobenzenesulfonate-reacted liposomes (or trinitrophenylated methylamine) suggesting close proximity of two labels is required for quenching. Conditions which promoted vesicular fusion promptly produced quenching. These differential labeling procedures can be usefully applied to quantitate aminolipids on internal and external vesicular surface, monitor vesicular fusion, and assess liposomal structure.     

Surface structures and sense organs of the cypris larva of Balanus balanoides as seen by scanning and transmission electron microscopy.

Various features of the settlement stage larva (cyprid) of the barnacle, Balanus balanoides (L.), were studied using scanning and transmission electron microscopy. The cuticle of the valves is pitted and in section has a characteristic ultrastructure. Small sensory setae protrode from the surface of this cuticle and are probably mechanoreceptors able to sense water movement around the larva. Each of the pair of caudla appendages which protrude from between the larval valves posteriorly, is made up of several sensory setae. These appendages are able to sense settlement surface topography. Certain other features of the larva are alos described and their roles discussed; such features include the frontal filaments, antennules and thoracic limbs.     

Regulatory factors produced by lymphocytes. I. The occurrence of multiple alpha-lymphotoxins associated with ribonuclease activity.

Supernatant fluids of mitogen-activated human tonsil lymphocytes contain large amounts of a factor toxic to mouse L cells. This substance, with a m.w. of 80,000 +/- 5,000 daltons, is called alpha-lymphotoxin (alpha-LT), to differentiate it from another toxin elaborated by mitogen activated human blood lymphocytes, called beta-lymphotoxin (beta-LT), which differs from alpha-LT in size (45,000 +/- 5,000 daltons), antigenicity, and stability. Further purification of alpha-LT by sequential phosphocellulose and DEAE-cellulose chromatography and polyacrylamide gel electrophoresis (PAGE) identifies a series of cytotoxins differing in ion exchange characteristics and electrophoretic mobilities. The three PAGE fractions (PAGE Ia, Ib and II), recovered in 2, 4.6, and 21% yield from the starting serum-free culture supernatant, represent purifications of 24-, 24- and 1851-fold, respectively. Each cytotoxic fraction has a ribonuclease activity. Comparison of RNase and mouse L cell cytotoxic activities of the three alpha-LT fractions shows that both activities for all three fractions have a similar temperature stability pattern and that both are similarly inhibited by DNA, single strand forms better than double strands, by glycerol in 5 to 20% concentration, and by protein denaturing reagents. These observations suggest, but do not prove, that mouse L cell toxicity and RNase activity are mediated by the same substance, which appears to occur in multiple or isozymic forms.     

Pre‐copulation intervals,copulation frequencies,and initial progeny sex ratios in two biotypes of whitefly,Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is a species complex, and its systematic classification requires controlled crossing experiments among its genetic groups. Accurate information on pre‐copulation intervals, copulation frequencies, and initial frequency of egg fertilization of newly emerged adults is critical for designing procedures for collecting the virgin adults necessary for these experiments. In the literature, considerable variation is reported between B. tabaci populations, with respect to the length of the pre‐copulation interval and the initial frequency of egg fertilization. Here, we used a video‐recording method to observe continuously the copulation behaviour of the Mediterranean/Asia Minor/Africa (B biotype) and the Asia II (ZHJ1 biotype) groups of B. tabaci. We also recorded the initial frequency of egg fertilization, as determined by the sex of the progeny. When adults were caged in female–male pairs on leaves of cotton plants, the earliest copulation events occurred 2–6 h after emergence; at 12 h after emergence 56–84% of the females had copulated at least once, and nearly all (92–100%) had copulated at least once by 36 h after emergence. Both females and males copulated repeatedly. Approximately 80 and 20% of copulation events occurred during the photophase and scotophase, respectively. By 72 h post‐emergence, the females of the B and ZHJ1 biotypes had copulated on average 6.1 and 3.9 times, respectively. When adults were caged in groups on plants 1–13 h after emergence, 30–35% of the eggs deposited during this period were fertilized, and approximately 90% of females were fertilized by the end of the 13 h. Although timing of copulation differed in detail between the two genetic groups, the results demonstrate that B. tabaci adults can start to copulate as early as 2–6 h post‐emergence and the majority of females can become fertilized on the day that they emerge.     

Copper resistance determinants in bacteria.

Copper is an essential trace element that is utilized in a number of oxygenases and electron transport proteins, but it is also a highly toxic heavy metal, against which all organisms must protect themselves. Known bacterial determinants of copper resistance are plasmid-encoded. The mechanisms which confer resistance must be integrated with the normal metabolism of copper. Different bacteria have adopted diverse strategies for copper resistance, and this review outlines what is known about bacterial copper resistance mechanisms and their genetic regulation.     

Fertility after bilateral cryptorchidism. Evaluation by paternity, hormone, and semen data.

PURPOSE: Evaluation of the fertility of a cohort of formerly bilaterally cryptorchid men in comparison with a group of formerly unilaterally cryptorchid men, and a group of control men. MATERIALS AND METHODS: Using a detailed questionnaire concerning paternity and factors related to paternity, a cohort of formerly bilateral cryptorchid men were studied and compared with men who had undergone orchiopexy for unilateral cryptorchidism, and a group of control men. All study subjects had had surgery at the Children's Hospital of Pittsburgh, Pittsburgh, Pa., between 1955 and 1975. A subset of the full cohort underwent clinical evaluation that included a physical examination, serum hormonal determination and semen analyses. RESULTS: Paternity rates are significantly lower among the formerly bilaterally cryptorchid men who have attempted to father a child (65.3%) as compared to the formerly unilaterally cryptorchid (89.7%; p < 0.001) and control men (93.2%; p < 0.001). Differences in the ability to father children are also apparent when semen and hormone levels are compared between the three groups. The bilateral group has significantly lower sperm density and inhibin B levels, and higher FSH and LH levels, than the unilateral and control groups. CONCLUSIONS: Men born with bilateral cryptorchidism have severely compromised fertility in adulthood. This reduction in fertility is clearly shown in comparisons of both paternity rates, and in semen and hormone analyses, between the formerly bilateral, formerly unilateral, and control groups.