Use of fluorescent probes in the study of phospholipid--sterol bilayers.

1. The transfer of excitation energy between the fluorescent probes 1,6-diphenylhexa-1,3,5-triene and 12-(9-anthroyl)stearic acid and the cholesterol analogue cholesta-4,6-dien-3-one in phosphatidylcholine liposomes has been investigated. 2. The results indicate that probes and steroid are randomly distributed in the bilayer at steroid concentrations up to 35 mol%. 3. The degree of polarization of diphenylhexatriene fluorescence increases with increasing cholesterol content. Other sterols, differing in structure in the region of the polar group or in the side chain at position-17, produce similar but not identical effects. 4. the results are consistent with the proposal that diphenylhexatriene gives a general picture of the state of the bilayer and that there is no segregation of sterols in liquid-crystalline phosphatidylcholine bilayers.     

Structure of bovine beta-lactoglobulin at 6A resolution.

Bovine β-lactoglobulin is a dimer with a molecular weight of 2 × 18,400. In solution it undergoes a pH-dependent transition at pH 7.0 between two alternative structures, named N and R. The structures of four different crystal forms have been determined by multiple isomorphous replacement with heavy-atoms. Two of them, lattices K and X, were crystallised at pH 6.5, corresponding to the N state in solution; and the other two, lattices Y and Z, were crystallised at pH 7.5, corresponding to the R state in solution. The figures of merit of the phase angles determined for these lattices were 0.76, 0.77, 0.80 and 0.80, respectively. The four structures that emerged are similar and show certain features suggestive of α-helices and pleated sheets, but the resolution is insufficient to trace the entire course of the polypeptide chain. No clear distinction can yet be made between the structures above or below pH 7.0, nor between the native molecule and the molecule from which the C-terminal leucine and histidine residues have been cleaved. Analyses at higher resolution are in progress.     

Epididymal sarcoidosis: a report of two cases and a review of the literature

Two cases of epididymal sarcoidosis, presenting as scrotal masses, are described. Biopsies of the epididymis and scalene nodes established the diagnosis. The literature of epididymal sarcoid and its differential diagnosis is discussed.     

Alcohol production by selected yeast strains in lactase-hydrolyzed acid whey

Ethanol production by Kluyveromyces fragilis and Saccharomyces cerevisiae was studied using cottage cheese whey in which 80 to 90% of the lactose present had been prehydrolyzed to glucose and galactose. Complete fermentation of the sugar by K. fragilis required 120 hr at 30°C in lactase-hydrolyzed whey compared to 72 hr in nonhydrolyzed whey. This effect was due to a diauxic fermentation pattern in lactase-hydrolyzed whey with glucose being fermented before galactose. Ethanol yields of about 2% were obtained in both types of whey when K. fragilis was the organism used for fermentation. Saccharomyces cerevisiae produced alcohol from glucose more rapidly than K. fragilis, but galactose was fermented only when S. cerevisiae was pregrown on galactose. Slightly lower alcohol yields were obtained with S. cerevisiae, owing to the presence of some lactose in the whey which was not fermented by this organism. Although prehydrolysis of lactose in whey and whey fractions is advantageous in that microbial species unable to ferment lactose may be utilized, diauxie and galactose utilization problems must be considered.     

The influence of snow conditions on the date of breeding of wading birds in north-east Greenland

The young of wading birds that breed in some parts of the arctic hatch when their insect food supply is most abundant. This appears to be the ultimate factor determining the date of egg-laying. In various other arctic birds the date of breeding may be influenced, directly or indirectly, by the time at which snow or ice melts. The Joint Biological Expedition to N.E. Greenland 1974 studied Ringed plovers Charadrius hiaticula , Dunlins Calidris aplina , Sanderlings Calidris alba , Knots Calidris canutus , and Turnstones Arenaria interpres breeding in various areas within 80 km of each other.
In 1974 the thaw was two or three weeks later than normal in the region. The time at which snow cleared and the dates of breeding of the waders differed considerably between valleys: breeding was delayed in valleys that cleared late. In all areas egg-laying ceased early in July, probably because chicks hatching from eggs laid later would not be ready to migrate by the end of the summer. Hence the mean date and length of the egg-laying period were determined by the date of snow clearance from the breeding areas.
Studies of the potential food resources indicate that the waders in N.E. Greenland do not appear to time their breeding so that the young hatch at some peak of food abundance. Sufficient food resources are probably available over a long period of time.     

p-Aminobenzoate biosynthesis in Escherichia coli. Purification of aminodeoxychorismate lyase and cloning of pabC

p-Aminobenzoate, a component of the vitamin folate, is one of seven compounds derived from the aromatic precursor chorismate in Escherichia coli. Historically the gene products of pabA and pabB were assumed to be sufficient for de novo p-aminobenzoate biosynthesis. Recent studies, however, have shown that these proteins, as nonidentical subunits of a single enzyme, act on chorismate to form a diffusible intermediate, most likely 4-amino-4-deoxychorismate. This intermediate is then converted to p-aminodeoxychorismate lyase (Nichols, B. P., Seibold, A. S., and Doktor, S. Z. (1989) J. Biol. Chem. 264, 8597-8601). Here we describe partial characterization of the intermediate and the purification of aminodeoxychorismate lyase 4100-fold to near homogeneity. Further purification of this enzyme by high pressure liquid chromatography permitted isolation of a pure sample that yielded N-terminal sequence. A 64-fold redundant oligonucleotide probe was used to identify a lambda clone containing the gene encoding aminodeoxychorismate lyase. The aminodeoxychorismate lyase gene, designated pabC, was mapped to 25 min on the E. coli chromosome and lies on a 7.5-kilobase pair EcoRI fragment. A strain harboring a pACYC184 recombinant containing pabC overproduced aminodeoxychorismate lyase activity 77-fold.     

Early adaptations in blood substrates, metabolites, and hormones to prolonged exercise training in man.

This study was designed to investigate the effect of short-term, submaximal training on changes in blood substrates, metabolites, and hormonal concentrations during prolonged exercise at the same power output. Cycle training was performed daily by eight male subjects (VO2max = 53.0 +/- 2.0 mL.kg-1.min-1, mean +/- SE) for 10-12 days with each exercise session lasting for 2 h at an average intensity of 59% of VO2max. This training protocol resulted in reductions (p less than 0.05) in blood lactate concentration (mM) at 15 min (2.96 +/- 0.46 vs. 1.73 +/- 0.23), 30 min (2.92 +/- 0.46 vs. 1.70 +/- 0.22), 60 min (2.96 +/- 0.53 vs. 1.72 +/- 0.29), and 90 min (2.58 +/- 1.3 vs. 1.62 +/- 0.23) of exercise. The reduction in blood lactate was also accompanied by lower (p less than 0.05) concentrations of both ammonia and uric acid. Similarly, following training lower concentrations (p less than 0.05) were observed for blood beta-hydroxybutyrate (60 and 90 min) and serum free fatty acids (90 min). Blood glucose (15 and 30 min) and blood glycerol (30 and 60 min) were higher (p less than 0.05) following training, whereas blood alanine and pyruvate were unaffected. For the hormones insulin, glucagon, epinephrine, and norepinephrine, only epinephrine and norepinephrine were altered with training. For both of the catecholamines, the exercise-induced increase was blunted (p less than 0.05) at both 60 and 90 min. As indicated by the changes in blood lactate, ammonia, and uric acid, a depression in glycolysis and IMP formation is suggested as an early adaptive response to prolonged submaximal exercise training.     

A complex pattern of H2A phosphorylation in the mouse testis

Phosphorylation of H2A histones in mouse testis was examined using testis tubule cultures labeled with 32PO4. Histones were analyzed by two systems of two-dimensional polyacrylamide gel electrophoresis, followed by autoradiography of the gels. Of the 32PO4 detected in histones, 95% was incorporated by certain modified forms of the H2A variants H2A.1 and H2A.X. Phosphorylation sites were mapped to N- and C-terminal regions of the modified variants by SDS gel electrophoresis and autoradiography of peptides generated by cleavage of in vitro-labeled proteins with N-bromosuccinimide. Incorporation rates differed for N- and C-terminal regions from different modified forms, demonstrating a complex pattern of H2A phosphorylation in the mouse testis.