Structural analysis of photosystem II in far-red-light-adapted thylakoid membranes. New crystal forms provide evidence for a dynamic reorganization of light-harvesting antennae subunits.

We studied two-dimensional crystals of the major pigment-protein complex, photosystem II, in far-red-light-adapted thylakoid membranes of the viridis-zb63 mutant of barley. Significantly larger grana membranes were produced with an increased synthesis of the entire photosystem II complex. These red-light-adapted membranes also contained two-dimensional crystals with a high frequency. Three different crystal forms of photosystem II were observed, providing the following data which further our understanding of the architecture of the native complex. (a) The oligomeric form of photosystem II in the membrane was monomeric in all crystal forms, but with a clear non-crystallographic pseudo-twofold symmetry. This was more apparent on the lumenal face of the complex. (b) The variability of unit cell contacts in different crystal forms implied that the peripheral light-harvesting antenna complex and the core of the complex were loosely connected. These peripheral subunits were predicted to rearrange so that they can either encircle the core complex or associate in parallel channels separated by lines of core complexes. (c) Grana membranes were found to retain a double-layered inside-out character, with a stromal face-to-stromal face packing. However, the presence of a crystal in one membrane did not necessarily impose crystallinity on its pair.     

Amidation of, and (R)-1-amino-2-propanol attachment to, the corrin ring during vitamin B-12 biosynthesis by Clostridium tetanomorphum extracts

Two intermediate stages in cobalamin biosynthesis, amidation of carboxylic acid groups in the corrin ring and (R)-1-amino-2-propanol attachment at propionic acid position f, have been studied using cell-free extracts from the obligate anaerobe Clostridium tetanomorphum. The preparation of an incomplete corrinoid, probably cobinic acid-a,c,d,e,g-pentaamide, as an in vitro amidation substrate was accomplished via mild acid hydrolysis of cobinamide. Weak, but reproducible activities for both amidation and (R)-1-amino-2-propanol attachment were found in crude, nucleic acid-free and DE-52 column-purified protein fractions. The amidation reaction was glutamine-dependent in crude fractions, but became ammonium ion-dependent in more purified fractions. Significant problems encountered were (a) the weak and unstable character of both enzyme activities, and (b) the irreversible changes in the visible spectra of the incomplete corrinoids employed as substrates caused by use of thiol-reducing agents in the buffers and assays.     

The location of exon boundaries in the multimeric iron-storage protein ferritin

Summary The nature of the amino acids whose codons border introns in ferritin genes is novel; the disposition of these intron boundaries within the three-dimensional structure of the 24-subunit molecule differs significantly from that of other proteins. These observations are discussed in relation to the functions of isoferritins.     

Isolation, Cloning, and Characterisation of a trp Homologue from Squid (Loligo forbesi) Photoreceptor Membranes

Abstract: The invertebrate phototransduction system is a valuable model of the ubiquitous inositol lipid signalling system. Taking advantage of the ability to obtain relatively large amounts of retinal material from the cephalopod eye, partial protein sequence data were obtained for a 92-kDa component isolated from a detergent-insensitive cytoskeletal fraction of a squid retinal microvillar membrane preparation. Degenerate oligonucleotides, designed on the basis of these sequence data, were used to isolate a full-length cDNA, encoding the 92-kDa component, using both cDNA library screening and 5'-rapid amplification of cDNA ends (5'-RACE) techniques. Comparison of the amino acid sequence encoded by this cDNA with entries in the OWL composite protein sequence database reveals greatest sequence similarity with the products of the Drosophila trp and trpl genes. Greatest variation from the Drosophila Trp protein is seen in the carboxyl-terminal region, which is considerably truncated in the squid protein and which accounts for most of the substantial difference in molecular weight seen between these proteins. This variation may be significant as the carboxyl-terminal domain has been shown to be in the regulation of several ligand-gated channels. The carboxyl-terminal domain has been expressed and shown to interact with calmodulin in a calcium-dependent fashion, thereby supporting this hypothesis. The likely occurrence of other homologues in a variety of systems suggests that this is a novel and important family of regulated ion channels involved in calcium signalling.     

An in vitro model of acetaldehyde metabolism by rodent conceptuses

Summary A culture model is described for the study of acetaldehyde (A_cH) metabolism by explanted postimplantation rat and mouse conceptuses. The ability of 12-d rat and 10-d mouse embryos to metabolise A_cH was demonstrated. The elimination rate for the 12-d rat conceptus using an initial A_cH concentration of 1 mM in the medium was found to be 1.8 nmol/mg per minute. When the conceptus was divided into embryonic and extraembryonic tissue, the rates were 1.6 and 2.2 nmol/mg per minute, respectively. When the A_cH concentration was reduced to 50 μM the rate was 0.095 nmol/mg per minute. The results provide further evidence for a functional barrier that prevents A_cH entry to the embryo. A comparative experiment using CBA/beige mouse conceptuses showed that A_cH elimination characteristics may be qualitatively similar to those in rat embryos, but that the estimated elimination rate of 0.8 nmol/mg per minute was less than half that of the rat. Thus the “metabolic barrier” may be less efficient in the mouse. This may be important in view of the greater sensitivity of the mouse to ethanol embryotoxicity. The work was supported by the King Edward Memorial Hospital Research Foundation and the Raine Research Foundation.     

Quieting response training: Treatment of psychophysiological disorders in psychiatric impatients

Self-regulation methods incorporating biofeedback are known to be useful in the treatment of psychophysiological disorders in psychologically normal patients. In this study, the effectiveness of Quieting Response (QR) training for the treatment of secondary psychophysiological complaints in psychiatric inpatients was assessed. Ten male and 27 female inpatients with a variety of secondary psychophysiological diagnoses were accepted into the study. Severely disturbed, confused, or depressed patients were excluded. All patients received QR training, which integrated EMG (electromyogram) and thermal feedback with breathing, progressive relaxation, and autogenic exercises. Daily practice of a 15-minute sequence of exercises was encouraged, and a 6-second reinforcement exercise was presented for use whenever an annoyance was encountered. No other therapeutic modalities were employed. Patients were followed for up to 2 years, and outcome was assessed with a multifactor quartile system. Rate of success at final follow-up for the inpatients (51%) was found to be equivalent to that of outpatients coming to the clinic with primary psychophysiological diagnoses (55%) and was not related to psychiatric diagnosis or nature of presenting complaint. Stepwise discriminant analysis indicated that older, less depressed individuals were more successful. Inpatients differed from nonpsychiatric patients only in the number of additional sessions received. Only one minor incident of increased psychopathology was observed. It was concluded that QR training was as effective for treating secondary psychophysiological disorders in all but the most severly disturbed inpatients as it was for the outpatient clinic population.This paper was presented at the Twelfth Annual Meeting of the Biofeedback Society of America, Louisville, Kentucky, March 1981. This project was funded in part by the van Ameringen Foundation. The authors gratefully acknowledge the contributions of Jane Archer and Jonathan Boren to the project.