Circadian rhythms in Neurospora crassa: the effects of point mutations on the proteolipid portion of the mitochondrial ATP synthetase

Summary Five oligomycin-resistant (oli ^r) mutant strains of Neurospora crassa were analyzed for their growth rate and for the periodicity of their circadian rhythm. The most resistant strains had periods of 18–19 h while the least resistant strain had a normal period of 21.0 h. There was a rough correlation between the in vivo degree of oligomycinresistance and the amount of change in the period. Several of the oli ^r mutations have been previously described by Sebald et al. (1977) in terms of known amino acid changes in the primary structure of the proteolipid, or DCCD-binding protein, found in the F₀ membrane portion of the mitochondrial ATP synthetase. Amino acid changes in the structure of this protein are reported here for two other oli ^r mutations. The proteolipid isolation procedures were slightly modified to include a delipidation step, and an HPLC procedure was developed to separate the hydrophobic peptides of this protein. Analysis of heterocaryons carrying both the oli ^r and oli ^s markers indicated that the oli ^r and oli ^s mutations were codominant to each other in terms of period and growth rate. The changes in the primary structure of this DCCD-binding protein reported here are the first known examples of changes in the primary structure of a protein which alter the period of a circadian rhythm.     

Photocontrol of Hypocotyl Elongation in Light-Grown Cucumis sativus L. : Responses to Phytochrome Photostationary State and Fluence Rate

The effects of the calculated photostationary state of phytochrome (_c) and the photon fluence rate on the elongation growth of the hypocotyl of light-grown seedlings of Cucumis sativus L. are examined. Two threshold responses to _c are found at values of 0.06 and 0.43. At _c = 0.06, there is no response at any fluence rate. In the _c range 0.1 to 0.43, elongation growth does not respond to changes in _c. Above the second threshold (_c = 0.43), there is a strong response to changes in _c. At all values of _c at and above 0.1, there is a response to fluence rate. A linear relationship can be demonstrated between a factor comprised of the logarithm of phytochrome cycling rate (a fluence-rate-dependent process) and _c, and the growth response.     

The presence and photoregulation of protochlorophyllide reductase in green tissues

Summary The enzyme protochlorophyllide (pchlide) reductase has been identified amongst the peptides, resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), of chloroplast membranes from oat and barley plants. In support of this identification the enzymic activity associated with the enzyme has also been measured in the same preparations. A higher level of enzyme was found in plants which had been darkened prior to extraction. Based on this data, mechanisms for the light regulated diurnal variation of the reductase are discussed.     

A comparison of the contractile activity of PGD2 and PGF2 alpha on human isolated bronchus

Prostaglandins may be implicated in the bronchoconstriction which occurs in asthma. Prostaglandins F2 alpha (PGF2 alpha) and D2 (PGD2) have been reported to produce bronchoconstriction in asthmatic subjects in vivo and PGF2 alpha contracts human isolated airway smooth muscle. We examined the relative efficacy and potency of PGF2 alpha and PGD2 on human bronchial spiral strips taken from 6 patients at thoracotomy. PGF2 alpha had greater efficacy than PGD2. The mean % Tmax (percentage of maximal contractile response) +/- s.e. mean were 84 +/- 7 and 54 +/- 7 respectively (P less than 0.05). PGF2 alpha (mean pD2 +/- s.e. mean = 6.39 +/- 0.6) tended to be more potent than PGD2 (5.68 +/- 0.2). Since, in vivo, PGD2 has greater efficacy and potency than PGF2 alpha, our results suggest that the in vivo effect of these prostaglandins does not result solely from an action on airway muscle.     

Arginine vasopressin causes morphological changes suggestive of fluid transport in rat choroid plexus epithelium

Summary The experiments described herein use an in vitro preparation of choroid plexus to demonstrate that it is a vasopressin-responsive organ by morphologic criteria. Choroid plexus from rats was incubated for one hour in graded concentrations of arginine vasopressin (AVP). Within physiologic range of molar concentration, incubation in vasopressin induced a decrease in basal and lateral spaces in choroid plexus epithelial cells as well as an increase in number of dark cells. The number of cells with basal spaces decreased significantly from 82.7±9.2 in control tissue to 19±18 in tissue incubated in 10^-12 M AVP; similarly, the number with lateral cellular spaces decreased from 20±8.8 to 7.6±2.2 cells in 10^-10 M AVP. Dark cells increased in number from 3.8±2.6 in control conditions to 49±4 with 10^-9 M vasopressin. These data suggest important effects of arginine vasopressin in cerebrospinal fluid (CSF) on choroid plexus, compatible with enhanced fluid transport across choroid epithelial cells.     

A novel chlorophyll a/b binding (Cab) protein gene from petunia which encodes the lower molecular weight Cab precursor protein.

The 16 petunia Cab genes which have been characterized are all closely related at the nucleotide sequence level and they encode Cab precursor polypeptides which are similar in sequence and length. Here we describe a novel petunia Cab gene which encodes a unique Cab precursor protein. This protein is a member of the smallest class of Cab precursor proteins for which no gene has previously been assigned in petunia or any other species. The features of this Cab precursor protein are that it is shorter by 2-3 amino acids than the formerly characterized Cab precursors, its transit peptide sequence is unrelated, and the mature polypeptide is significantly diverged at the functionally important N terminus from other petunia Cab proteins. Gene structure also discriminates this gene which is the only intron containing Cab gene in petunia genomic DNA.     

The acetyl-CoA pathway of autotrophic growth

Abstract The most direct conceivable route for synthesis of multicarbon compounds from CO₂ is to join two molecules of CO₂ together to make a 2-carbon compound and then polymerize the 2-carbon compound or add CO₂ successively to the 2-carbon compound to make multicarbon compounds. Recently, it has been demonstrated that the bacterium, Clostridium thermoaceticum , grows autotrophically by such a process. The mechanism involves the reduction of one molecule of CO₂ to a methyl group and then its combination with a second molecule of CO₂ and CoA to form acetyl-CoA. We have designated this autotrophic pathway the acetyl-CoA pathway [1]. Evidence is accumulating that this pathway is utilized by other bacteria that grow with CO₂ and H₂ as the source of carbon and energy. This group includes bacteria which, like C. thermoaceticum , produce acetate as a major end product and are called acetogens or acetogenic bacteria. It also includes the methane-producing bacteria and sulfate-reducing bacteria.
The purpose of this review is to examine critically the evidence that the acetyl-CoA pathway occurs in other bacteria by a mechanism that is the same or similar to that found in C. thermoaceticum . For this purpose, the mechanism of the acetyl-CoA pathway, as found in C. thermoaceticum , is described and hypothetical mechanisms for other organisms are presented based on the acetyl-CoA pathway of C. thermoaceticum . The available data have been reviewed to determine if the hypothetical schemes are in accord with presently known facts. We conclude that the formation of acetyl-CoA by other acetogens, the methanogens and sulphate-reducing bacteria occurs by a mechanism very similar to that of C. thermoaceticum .     

A test of the hypothesis of pheromone attraction in salmonid migration

Synopsis We tested the hypothesis that anadromous salmonids are guided on their homeward migration by population-specific pheromones. Our findings do not support the hypothesis. Wild migrant Arctic charr,Salvelinus alpinus, from Ikarut River, Labrador were transferred and held in a tributary previously uninhabited by anadromous fish. None of the charr migrating up Ikarut River entered the tributary after fish were transferred. Similarly, migrant charr, which were caught in Ikarut River and released in the tributary below the captive fish, did not remain in the tributary. We re-evaluated the data which have been used to uphold the concept of pheromone attraction in salmonid migration and concluded that support for the hypothesis is unsubstantiated.     

The impact of diagnostic tests in evaluating patients with syncope

We reviewed the charts of 100 patients admitted to the hospital for evaluation of syncope. The charts were examined with special attention given to the causes of syncope, the frequency and benefit of diagnostic tests, and the relative cost of these tests. In 39 patients no etiology for syncope was found, and another 18 were felt to have had a vasovagal episode. Twelve patients had arrhythmias as the cause for syncope. Most of the patients underwent a variety of diagnostic tests including cardiac enzyme determinations, brain scans, electroencephalograms, head CAT scans, and Holter monitoring. In most instances, these tests added little useful information to the initial history and physical exam and were done at great expense to the patient. Our data suggest that extensive neurologic testing in patients with "routine" syncope is not warranted and that the focus of hospitalization should be to rule out potentially life-threatening arrhythmias.