Evidence from cDNA clones that the rat leukocyte-common antigen (T200) spans the lipid bilayer and contains a cytoplasmic domain of 80,000 Mr

The leukocyte-common antigen (L-CA or T200) includes a family of lymphoid and myeloid cell surface glycoproteins with apparent molecular weights from 180,000 to 240,000. We report a partial protein sequence for thymocyte L-CA containing 1073 amino acids predicted from cDNA clones isolated using an oligonucleotide probe. Only one segment (residues 347-368) is likely to cross the membrane, and peptide data suggest that sequences N-terminal to this are outside the cell, with residues 369-1073 inside. The cytoplasmic domain includes possible phosphorylation sites and an internal homology between residues 385-671 and 676-986. Analysis of B lymphocyte cDNA clones suggests that B cell and thymocyte mRNAs are identical in 3' sequences, but size differences in Northern blots suggest 5' sequences may differ.     

A rapid naphthol yellows method for measuring the cellular protein content of anchorage cultures

Summary A rapid method has been developed for measuring the cellular protein content of mono- and multilayered anchorage cultures. Fixed or air dried cultures are stained for 30 min with 0.2% Naphthol Yellow S (NYS) dissolved in 1% acetic acid. Unbound dye is removed by a series of four 2.5 min washes in 1% acetic acid, and protein-bound dye extracted with 10 mM unbuffered Tris base for spectrophotometric optical density determination at 433 nm. The NYS method exhibited a least-squares correlation coefficient of 0.99997 with the Oyama-Eagle Lowry method.     

Transport of chlorine in the proximal tubule. Its effects on water-electrolyte absorption

Several studies in rat kidney have established that an appreciable fraction of proximal absorption is passive in nature and occurs across the highly conductive paracellular pathway. Passive absorption is generally ascribed to the transepithelial Cl- distribution, luminal Cl- activity (alpha lCl) being higher than plasma Cl- activity (alpha pCl). The inequality alpha lCl greater than alpha pCl generates a transepithelial diffusion potential, lumen positive, which taken together with the chemical potential differences of Cl- and Na+ across the epithelium gives rise to transepithelial electrochemical potential differences for Cl- and Na+ favoring their absorption. The alpha lCl greater than alpha pCl distribution is traditionally ascribed to preferential bicarbonate absorption. We argue that HCO3- absorption alone cannot generate a non equilibrium transepithelial Cl- distribution. Other mechanisms are necessary. Our measurements in amphibian proximal tubule demonstrate that the intracellular Cl- activity, alpha cCl, is higher than the theoretical value predicted for equilibrium. This distribution is the result of two basolateral coupled transport processes (Cl-/HCO3- exchange and Cl-/Na+ cotransport). It contributes to the exit of Cl- from cell to lumen (by passive diffusion and K+/Cl- cotransport), yielding alpha lCl values higher than the theoretical value for equilibrium with regard to plasma. Thus, a small transcellular flux of Cl- (without solvent) proceeds from interstitium to lumen. It compensates the dissipative tendency of a much higher paracellular Cl- absorptive flux (in association with water) on the transepithelial Cl- gradient. The result is a steady-state luminal Cl- distribution above equilibrium, along the major part of the proximal tubule.     

Nonvisual feeding in a visual planktivore,Xenomelaniris venezuelae

Summary Studies of the diel feeding patterns of the planktivorous fish, Xenomelaniris venezuelae, in Lake Valencia, Venezuela, revealed that, although the fish is primarily a diurnal feeder, it consumes substantial numbers of Chaoborus larvae and pupae at night. A number of fish species are known which feed on plankton at night, but these fish are filter feeders and their diets largely consist of relatively small, nonevasive prey. Chaoborus, however, is large and agile. Predation by Xenomelaniris in the dark was also studied experimentally. Captured fish were placed in completely darkened aquaria with zooplankton from Lake Valencia. After several hours the plankton was removed and examined for evidence of feeding. The fish were found to consume Chaoborus pupae and fourth instar larvae but not other types of prey. The mode of feeding by Xenomelaniris in the dark is unknown.     

An experimental removal of a territorial pomacentrid: effects on the occurrence and behavior of competitors

Synopsis Stegastes fasciolatus is the most common territorial damselfish in the shallow waters of Hawaii. Territorial defense was observed against other herbivorous fishes, especially acanthorids, scarids and one omnivorous chaetodontid. One acanthurid,Acanthurus nigrofuscus was found to differ in abundance and social behavior in areas whereS. fasciolatus was present, compared to areas where it was absent. The chaetodontid,Chaetodon quadrimaculatus was sheltered during the day in areas where the pomacentrid was abundant, apparently feeding at night. In other areas it fed during the day and at night, depending on the phase of the moon.S. fasciolatus were then experimentally removed from one study site, to test whether the differences in abundance and behavior of the other species were due to the presence of the damselfish. There was a significant increase in numbers of the surgeonfishAcanthurus nigrofuscus in the removal area, as well as changes in social behavior from schooling to defense of small territories. The butterflyfish,C. quadrimaculatus, was observed to forage during the day in the removal area. There were no significant changes in the control sites. The presence of the interspecifically territorial damselfish,S. fasciolatus, thus appears to be an important determinant of the behavior of these potential food competitors.     

INCIDENTAL MORTALITY OF NORTHERN SEA LIONS IN SHELIKOF STRAIT, ALASKA

The incidental catch of northern sea lions ( Eumetopias jubatus ) in the walleye pollock ( Theragra chalcogramma ) joint-venture fishery in Shelikof Strait, Alaska, was studied during 1982–1984 to assess the nature and magnitude of the catch. Data were obtained by placing U.S. observers on foreign processing vessels. Dead sea lions recovered from trawl nets were counted, sexed and measured, teeth were removed for age determination by dental laminae; and stomach contents were analyzed. Although the fishery has continued to expand both in number of boats and estimated total catch (74,136 metric tons [t] in 1982 to 171,539 t in 1984), the estimated incidental catch of northern sea lions has declined (ranging from 958 to 1,436 in 1982, 216 to 324 in 1983 and 237 to 355 in 1984). Of the sea lions processed, 73 percent were caught between 2000 and 0500 h, probably during net retrieval. Most caught sea lions were females ranging in age from 1–25 yr with a mean age of 6.43 yr; 79 percent of the females were sexually mature and probably part of the reproducing population. Males had a mean age of 4.8 yr and only 12 percent were old enough to obtain and defend territories. Analysis of stomach contents showed that the sea lions consumed pollock the same size as that taken by the commercial fishery. The impact of the incidental catch on the Gulf of Alaska sea lion population is unknown.     

A simple method to purify ribonucleotide reductase

Assays of ribonucleotide reductase in extracts of Detroit 98 (human) cells were found to be complicated by the rapid depletion of the substrate (CDP) by nucleoside diphosphate kinase. Assays of either 100,000g supernatants or ammonium sulfate-fractionated extracts resulted in the conversion of >90% of the substrate to CTP within 2 min. It was therefore desirable to separate nucleoside diphosphate kinase from ribonucleotide reductase. Chromatography of the fractionated extract on an ATP-agarose column resulted in the delivery of nondissociated ribonucleotide reductase in the void volume and the retention of >99.9% of the nucleoside diphosphate kinase. The kinase could be eluted by 2 mm ATP. The ribonucleotide reductase was recovered from this commercially available gel with an apparent yield of >200%. It could be accurately assayed with only minimal extraneous depletion of substrate. Furthermore, it was stable to storage at ?80°C. Tris-HCl was found to inhibit the enzyme. When HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid)-Na buffer was used in place of Tris-HCl, the rate of CDP reduction was increased by 2.5-fold. Since the above procedure selectively removes nucleoside diphosphate kinase from crude preparations of ribonucleotide reductase, it should have general applicability for purifying ribonucleotide reductase from other sources.     

Human placental 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase. Studies with 6 beta-bromoacetoxyprogesterone

Two soluble enzyme activities, 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase, copurified from the cytosol fraction of human term placenta, were identically inactivated by 6 beta-bromoacetoxyprogesterone. This affinity alkylating steroid binds at the enzyme-active site (Km = 866 microM; Vmax = 0.073 mumol/min/mg). Enzyme inactivation by four concentrations of 6 beta-bromoacetoxyprogesterone (molar ratio of steroid to enzyme, 71/1 to 287/1) causes irreversible and time-dependent loss of both the 17 beta- and 20 alpha-activities according to first order kinetics and affirms that the alkylating steroid is an active site-directed inhibitor (KI = 2.7 X 10(-3) M; k3 = 1.6 X 10(-3) s-1). Affinity radioalkylation studies using 6 beta-[2'-14C]bromoacetoxyprogesterone indicate that 2 mol of steroid are bound to each mole of inactivated enzyme dimer (Mr = 68,000). Amino acid analyses of the acid hydrolysate of radioalkylated enzyme show that 6 beta-bromoacetoxyprogesterone carboxymethylates cysteine (56%), histidine (22%), and lysine (8%) residues in the active site. These results are identical with those reported for 2-bromo[2'-14C]acetamidoestrone methyl ether radioalkylation of purified "17 beta-estradiol dehydrogenase." The parallel inactivation of 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase by 6 beta-bromoacetoxyprogesterone further shows that both activities reside at a single enzyme-active site. The radioalkylation profile supports our proposed model of one enzyme-active site wherein the bound progestin and estrogen substrates are inverted, one relative to the other.     

An age dependent stochastic model of periodic screening: Basic properties

An age dependent stochastic model for the periodic screening of a progressive chronic disease is developed in this paper by combining results from previous modeling efforts. The basic concepts used are the random variables describing the disease free state and preclinical state sojourn times and the age at screening or observation, as well as generations of individuals defined according to time of entry into the preclinical state. At discrete time points, the model characterizes the density functions for individuals who are healthy, have preclinical disease, or have clinical disease. The joint density functions of age and sojourn times for cases detected by a periodic screening program and for cases which surface clinically between screens are derived as functions of screening interval, false negative rate, and disease natural history.