Graphic analysis of superoxide secretion by phagocytic leukocytes at different cell concentrations.

Superoxide secretion by monocytes, macrophages and neutrophils becomes less efficient in a non-linear manner as the cell concentration is increased. This relation holds for cells in suspension or attached to a substrate, elicited into the peritoneum with various agents or from the peripheral circulation, acutely stimulated with particulate or soluble agents, and in experimental animals and in man. The significant observation of this study is that in all these systems, of data from our own studies as well as from the literature, plots of the logarithm of superoxide secreted per cell per unit of time versus the logarithm of the cell concentration were linear with correlation coefficients better than 0.98. The common practice of comparing data on superoxide secretion from experiments performed at different cell concentrations is clearly unsatisfactory. It is suggested that superoxide secretion be expressed in terms of both the slope of the log log plot and the secretion rate at a given cell concentration.

Proposed loci of interaction between bombesin and its receptor.

The non-coding strand of the bombesin receptor gene, when 'translated' 5' to 3', contains an interrupted sequence of the 10 amino acids of bombesin. This finding forms the basis for proposing the points of contact between bombesin and its receptor as well as a partial conformation of the binding region of the receptor.

In vitro ultrastructural localization of the catalytic activity of adenosine deaminase in murine C-1300 neuroblastoma.

Adenosine deaminase (ADA) activity was localized at the surface membrane of the mouse C-1300 neuroblastoma by incubation of a confluent tissue culture monolayer grown on Lux-Permanox cultureware with 6-chloropurine ribonucleoside (CPR). This substrate is dechlorinated by ADA to form Cl-. At loci of ADA activity, Cl- is precipitated with added silver ion (Ag+), and electron dense metallic silver (Ag degree) is formed upon exposure to light. The incubation was conducted in 0.2 M HEPES buffer (277 mOs) at 37 degrees C, pH 7.4, which contained 1 mM CPR, for 5 min (in this buffer, this is four times the Km); the control lacked the substrate. After completion of the incubation, the monolayer was briefly rinsed with 0.2 M HEPES and 2.5% glutaraldehyde in 0.2 M HEPES containing AgNO3 at a final concentration of 2 mM. Dehydration was accomplished in a graded series of ethanol followed by embedment in the L. R. White resin at 60 degrees C overnight. Thin sections (80 to 100 mm), cut parallel to the monolayer, showed ADA activity at the cells' surface membrane with a smaller amount of activity evenly distributed in the subadjacent ectoplasmic zone. The control lacked any silver grain localization. Since in preliminary studies of neuronal tissue the ADA activity was minimal, these findings may contribute to developing a diagnostic cancer screening test.

A model for hydropathy-based peptide interactions.

Two peptides are specified when the noncoding DNA strand is read in the 5' to 3', or the 3' to 5' direction, and both peptides form strong complexes with the natural peptide, as found by J. E. Blalock and K. L. Bost with ACTH [1986) Biochem. J. 234, 679-683). We report here that strong hydropathic complementarity (pairing of hydrophobic with hydrophilic residues), the assumed basis of these interactions, is obtained only if the peptide resulting from reading in the 3' to 5' direction is aligned parallel to the natural peptide, or if the peptide derived by opposite reading of the DNA is aligned antiparallel to it. Complementary is abolished in other alignments, including all staggered ones. In the appropriate alignments of the constructs the amino acid residues opposite one another are specified by a pair of complementary codons in the DNA; Blalock and Bost have indeed shown that complementary pairs of codons specify amino acids of opposite hydropathy. A model is proposed to explain how hydropathic complementarity can lead to interaction between peptides. We propose that in the interacting peptides hydrophilic residues of both chains are oriented toward the aqueous solvent, while the hydrophobic ones form the interphase between the two chains. Tight packing is made possible by the stipulation that whenever a hydrophilic residue turns toward the aqueous phase, a space is liberated which can accommodate a hydrophobic residue from the opposing chain. This entropy-driven configuration can lead to strong interactions between portions of peptides consisting of hydropathically complementary residues.

Ecto-enzyme activity of human erythrocyte adenosine deaminase.

Adenosine deaminase is found primarily in the cytoplasm of many cell types. In the human erythrocyte, about 30 per cent of the total adenosine deaminase activity is membrane associated, and about two-thirds of this is inactivated by treatment of intact erythrocytes with the nonpenetrating reagent diazotized sulfanilic acid, without affecting lactate dehydrogenase, a soluble cytoplasmic enzyme. This indicates that within the cell membranes, the catalytic site of about two-thirds of the adenosine deaminase faces the external medium, i.e., ecto adenosine deaminase. Localization of adenosine deaminase activity at the cell membrane is demonstrated directly by electron microscopy by use of the substrate 6-Chloropurine ribonucleoside, which is dechlorinated by adenosine deaminase to produce Cl-, which is precipitated at its locus of formation by added Ag+, and the precipitated AgCl converted into the electron dense Ag0 upon exposure to light. From the Hydropathic Profile of the amino acid sequence of adenosine deaminase it is evident that there are two hydrophobic domains of sufficient length to span a biological membrane, and it is proposed that these domains could function to anchor the enzyme to the membrane. The importance of adenosine deaminase is indicated by the fatal immuno-deficiency which results from untreated genetic adenosine deaminase deficiency. It may be important to determine whether the amount of ecto adenosine deaminase activity is better suited to assess the clinical status of adenosine deaminase deficient patients that the currently used total cellular enzyme activity.

Circadian rhythms of adenosine deaminase activity in human erythrocytes: a transverse study on young, elderly and senile demented subjects.

Adenosine deaminase activity (ADA) was determined around the clock in human plasma from different groups of subjects: presumably clinically healthy women in Minneapolis, USA; healthy medical students, healthy elderly men and women, and mentally ill patients in Paris, France. In addition to analyses of variance, circadian characteristics were estimated individually and summarized by population-mean cosinor for each group. Technical and sampling considerations are documented: the individualized assessment of a circadian rhythm in adenosine deaminase is feasible in 8 out of 11 series from clinically healthy women covering 24h at 20-min intervals. A circadian population rhythm could be determined for the elderly men and women (p less than 0.05) and tentatively (p = 0.053) for the senile demented patients. A difference in circadian group rhythm characteristics found between the healthy elderly subjects and patients with senile dementia deserves further exploration.

Kinetics of formation of renotropic growth factor.

In the Wistar/Furth rat, twenty-four hours after unilateral nephrectomy, the remaining contralateral kidney produces maximum amounts of renotropic growth factors. These factors stimulate tumor growth in recipient rats with s.c. Wilms tumor, but have no effect on kidney weight. In tumor-free recipients, kidney hypotrophy results when the factors are administered.

Specificity of renotropin receptors in murine Wilms tumor model.

Contralateral kidneys, removed forty-eight hours after unilateral nephrectomy, contain renotropic growth factors with different effects on normal kidney and Wistar/Furth rat Wilms tumor. Receptors on tumor cells bind factors which, when eluted followed by in vivo bioassay, stimulate the growth of Wilms tumor. Receptors on normal kidney cortex cells bind factors which, when eluted, produce kidney hypotrophy in nontumor-bearing rats.

Adenosine deaminase activity associated with phagocytic vacuoles. Cytochemical demonstration by electron microscopy.

Adenosine deaminase activity has been localized within the cell membrane and it surrounds phagocytic vacuoles in mouse macrophages. Adenosine deaminase is thus strategically located to direct metabolic flux through the enzymes of the purine catabolic pathway. Xanthine oxidase, a key enzyme of this pathway, produces superoxide during its reaction with its substrates. Enzyme activity was visualized for electron microscopy by means of hydrolysis of 6-Chloropurine ribonucleoside to produce Cl-, which is precipitated with Ag+. The latter is converted into Ag0 by light, and the resulting deposit is visualized with the electron microscope.

Modulation of macrophage superoxide release by purine metabolism.

Metabolic flux through the purine salvage pathway appears to modulate superoxide secretion by elicited macrophages. Exogenous adenosine, the first substrate of this pathway, stimulates superoxide secretion, and Allopurinol, a specific inhibitor of xanthine oxidase, inhibits superoxide secretion. The effects of these agents are additive since it was possible for each to neutralize the effects of the other when given in combination. In these experiments, the purine salvage pathway was responsible for over ten times the superoxide production attributable to the NADPH oxidase system.

Validity of the continuous spectrophotometric assay of Kalckar for adenosine deaminase activity.

Both adenosine and inosine obey Beer's law to 1.0 mM at 265 nm and pH 7.4 at 25 degrees C. Murphy et al. (1) claimed serious deviation from Beer's law above 200 microM for both substances, and concluded that the assay of adenosine deaminase activity based on recording spectrophotometric change at 265 nm as originally suggested by Kalckar produces anomalous results. The data herein presented show that this is not so, and that the large number of published studies of adenosine deaminase activity assayed by this method are indeed valid and should not be dismissed as artifactual as suggested by Murphy et al.

Removal of superoxide dismutase activity from cytochrome C.

Commercially available cytochrome c contains sufficient superoxide dismutase activity to reduce its sensitivity in superoxide anion detection. A single passage through a column of Sephadex G-50 removes the superoxide dismutase, and appreciably increased the ability to cytochrome c to detect superoxide.