Comparison of chemical properties of purified plasma membranes and secretory vesicle membranes from the bovine adrenal medulla

Summary A highly enriched fraction of plasma membranes from the bovine adrenal medulla has been isolated by differential and sucrose gradient centrifugation. The membranes were found to occur as 0.1–0.5 diameter vesicles and to equilibrate at a density of 1.13–1.14 g/ml. This fraction was characterized by 4-fold elevated levels of adenylate cyclase and 20-fold elevated levels of 5-nucleotidase. Secretory vesicle membranes, isolated by repeated hypotonie and hypertonic shocks of whole vesicles, were found to equilibrate between d = 1.08 and d = 1.12 on a sucrose density step gradient. These membranes were highly enriched in cytochrome b₅₆₂ and dopamine--hydroxylase. Proteins in the two membranes were compared by SDS gel electrophoresis. All protein size classes found in the vesicle membrane fraction were also represented in the plasma membrane fraction, though in different proportions on the basis of staining intensity. The plasma membrane fraction contained prominent bands co-migrating with the - and -bands of tubulin, as well as a component co-migrating with actin. These bands were absent from the vesicle membranes. Fingerprint analysis of stained bands from the membrane fraction demonstrated that the components were indeed tubulin and actin. The plasma membranes contained twice as much sialic acid residues as did the chromaffin granule membranes, but had only half the cholesterol content on a weight basis. The cholesterolphospholipid ratio in the plasma membranes was 0.63, while in the secretory vesicle membranes it was 1.04. These results show that plasma membranes and secretory vesicle membranes are functionally and structurally different.Supported, in part, by a stipend to O.Z. from The Grant Foundation, New York     

Phagocytosis and killing of bacteria and yeast by human milk cells after opsonisation in aqueous phase of milk.

Macrophages and neutrophils from human milk phagocytose and kill Staphylococcus aureus and Escherichia coli in vitro after opsonisation by the aqueous phase of milk as effectively as blood leucocytes in serum. They also phagocytose Candida albicans. The overgrowth of E coli resulting from the addition of iron to cultures of the organism in the aqueous phase of milk is not influenced by the presence of cells. We conclude that the phagocytosis and killing of bacteria by milk cells may contribute to the lower incidence of infection among breast-fed than artificially fed babies.     

Lordosis: Inhibiting effects of progesterone in the female rat

Progesterone has two types of inhibitory effects on female sexual behavior that have been well-documented in the guinea pig. The first occurs when high levels of progesterone are present around the start of the estrogen-priming process (“concurrent inhibition”). The second occurs immediately after the display of an estrogen-progesterone-induced period of estrous behavior (“sequential inhibition”). In the present set of experiments, we show that the rat, like the guinea pig, is capable of exhibiting both of these inhibitory effects of progesterone. However, rats require higher doses of progesterone than guinea pigs, at least for concurrent inhibition to be evident. In addition, we show that the dose of progesterone required in a single injection to produce concurrent inhibition is higher than the dose required to produce sequential inhibition in rats. A theory of how progesterone may be accomplishing its inhibitory effects on female sexual behavior in rodents is presented.     

Proteins synthesized by inducer T cells: evidence for a mitogenic peptide shared by inducer molecules that stimulate different cell types

Inducer T lymphocytes synthesize and secrete peptides that stimulate growth and differentiation of many cell types, including lymphocytes and monocytes that kill foreign organisms, B lymphocytes, mast cells and hematopoietic precursor cells. To define these inducer molecules more precisely, we have generated clones of these T cells as a source of homogeneous material for biochemical analysis. These clones synthesize peptides that stimulate T and B cells to divide and that also induce the latter cells to secrete immunoglobulin. Inducer cells synthesize a 14 kilodalton growth polypeptide that stimulates T and B lymphocytes, as well as other cell types, to divide. This 14 kilodalton peptide is normally associated with different, larger peptides that appear to focus its mitogenic activity to one or another target cell.     

The validity of the lead precipitation technique for the localization of ATPase activity in plant cells

Summary The claim that osmium-containing deposits which lack lead are frequently and incorrectly interpreted as enzymatic reaction products in lead precipitation techniques for ATPase localization in plants is without foundation. Proper controls clearly demonstrate the enzymatic origin of membrane-located deposits and the presence of lead is confirmed by analytical electron microscopy.     

The size of the extracellular space in the isolated midgut ofManduca sexta

The size of the extracellular space in the isolated midgut ofManduca sexta measured statically with labeled sucrose and with labeled inulin was 48 and 50 percent of tissue water respectively. Both labeled sulfate and labeled mannitol yielded loading spaces which approached the volume of the tissue water with increasing pulse time and are not valid markers of the extracellular space. A washout method yielded unreliable values for the sucrose and inulin spaces and its use cannot be justified using presently available midgut chamber designs. Values of the sucrose space measured statistically in this study and other studies using different Lepidopteran larvae and different perfusion chambers range from 42 to 48 percent of the tissue water. Agreement between published values of the sulfate space and these values of the sucrose space is fortuitous, the labeling pulses being short enough to yield approximately half saturation of the actual sulfate loading space.     

Half-lives of messenger RNA species during growth and differentiation of Dictyostelium discoideum

The half-lives of functional messenger RNAs were determined by a method employing the drugs actinomycin D and daunomycin for the inhibition of mRNA synthesis; the activity of extracted mRNAs was determined by an in vitro translation assay. Several controls indicated that this method yielded reliable values for mRNA half-lives; in particular, the declining rate of protein synthesis in the presence of the drugs is due predominantly to the decay of translatable mRNA. This method was used to determine the half-lives of two specific mRNAs—encoding actin and a protein of MW 51,000—as well as that of total cytoplasmic mRNA activity during growth and at several times in differentiation. The half-lives of at least these two mRNAs were shown to be distinctly different from that of the total mRNA population—about 4 hr. However, no significant change in any of these half-lives was observed between growing and developing cells. Therefore wholesale alterations in the degradation rates of total and at least specific messages do not appear to play a role in the regulation of gene expression during Dictyostelium development.     

The evolution of conspicuous coloration: Some experiments in bad taste

Unpalatable species are often brightly coloured. Such aposematic coloration may have evolved because predators can learn to avoid conspicuous prey more readily than cryptic prey. Experiments on young male chicks are described and the results are consistent with this hypothesis.     

Primary induction of metallothionein by dexamethasone in cultured rat hepatocytes

Dexamethasone or Zn⁺⁺ increase the rate of synthesis of the metal-binding protein metallothionein in hepatocyte cultures. Dexamethasone induction of the capacity to synthesize metallothionein is not blocked by cycloheximide. In contrast, the dexamethasone stimulated increase in Zn⁺⁺ uptake is inhibited by cycloheximide. Like Zn⁺⁺, dexamethasone is a “primary inducer” of metallothionein. The glucocorticoid induction of metallothionein in primary cultures of rat hepatocytes is not mediated through elevation of Zn⁺⁺ uptake.