Subunit structure of submitochondrial particle membrane transhydrogenase

The subunit structure of membrane-bound mitochondrial transhydrogenase was investigated. Chemical modification of bovine heart submitochondrial particles with the cleavable bifunctional cross-linking reagent, dithiobis(succinimidyl propionate), resulted in the formation of three dimeric "cross-link isomers" of the enzyme, identified by immunoautoradiography, that are characteristic of cross-linked purified transhydrogenase. A limited amount of cross-linking of transhydrogenase monomer to Mr = 25,000 polypeptide was also observed. At high concentration of the cross-linker, a small amount of a higher molecular weight species was formed with both purified and membrane enzyme. Reductive cleavage of the dimeric and higher molecular weight species resulted in the regeneration of transhydrogenase monomer and several other proteolytically derived fragments. It is concluded that transhydrogenase exists in the native membrane primarily as a dimeric species.     

ORGANIC COMPOUNDS RELEASED FROM A NATURAL POPULATION OF EPIBENTHIC BLUEGREEN ALGAE1

Extracellular release of dissolved organic compounds by the bluegreen algal community of a brackish marsh was studied using ¹⁴C techniques. Mannitol and trehalose were identified as the most commonly released compounds. The proportions of these two extracellular compounds varied in response to light intensity and the water potential of the environment. The presence of mannitol, in particular, suggests that excretion of organic compounds in natural situations is a function of osmotic adjustment.     

Control of bud inhibition in Cyperus

Summary The axillary buds in the leaf crown of Cyperus alternifolius seedlings remain completely inhibited although the shoot is determinate and has no active apex. Buds can be released by detachment of the crown from the plant or by direct application of aqueous enzyladenine (BA), and grow out as inflorescences or vegetative shoots. These arise from activated growth centers of the primordial reproductive branch system which is enclosed within the prophyll of the inhibited bud. Buds are also released by the growth retardant, (2-chloroethyl) trimethylammonium chloride (CCC). Gibberellic acid maintains bud inhibition in detached crowns and inhibits bud release caused by CCC or BA. Naphthaleneacetic acid somewhat reduces BA-induced bud release and causes abnormal root proliferation in CCC-treated crowns. It is suggested that a high level of gibberellin within the crown, possibly in relation to a low level of cytokinin, maintains bud inhibition.     

COMPARATIVE ULTRASTRUCTURE OF CULTURED SPECIES OF TREBOUXIA1,2

Five species of cultured Trebouxia—T. anticipata, T. decolorans, T. erici, T. gelatinosa, and T. impressa—were examined with the electron microscope. A comparative examination of their pyrenoids revealed pyrenoglobuli associated with single pyrenoid thylakoids. The pyrenoids of T. decolorans, T. erici, and T. gelatinosa possess single thylakoids that cross or deeply penetrate the pyrenoid matrix and are often disposed in parallel arrays. T. anticipata possesses both single and double pyrenoid thylakoids within the matrix. T. impressa possesses vesiculate invaginations of thylakoid membranes into the pyrenoid matrix. The phycobiont. T. erici was examined in detail at the light and electron microscopic levels for pyrenoid alterations associated, with varied environmental regimes and with cell division. A greater amount of starch is present in cells grown in organic culture at 215 lux light intensity than in cells of similar size grown at 1075 or 3600 lux. Pyrenoglobuli are present throughout the life cycle and occur both in aplanospores and in zoospores.     

Affinity labelling of the binding site of rabbit antibody. Evidence for the involvement of the hypervariable regions of the heavy chain

The binding sites of rabbit antibodies with affinity for the haptenic group 4-azido-2-nitrophenyl-lysine have been specifically labelled by photolysis of the hapten-antibody complex. The extent of covalent labelling was 0.5-0.9mol of hapten bound/mol of antibody and, by using an immunoadsorbent, antibody with 1.3mol of hapten/mol was obtained. The antibody was specifically labelled in the binding site and the ratio of labelling of heavy and light chains was in the range 3.3-5.0. The labelled heavy chains were cleaved by CNBr treatment and after reduction and alkylation of the intrachain bonds, were digested with trypsin. Evidence is presented that two regions of the heavy chain, positions 29-34 and 95-114, together contain about 80% of the label on the heavy chain; these two regions respectively include two of the hypervariable regions of rabbit heavy chain.