Dynamic changes of serum gamma-glutamyl transferase in chronic alcoholism.

Elevated serum gamma-glutamyl transferase (GGT) levels were found in 29% of 155 chronic alcoholics undergoing detoxification treatment. Alkaline phosphatase (AP) was increased in 16%, alanine aminotransferase--SGPT (ALT) in 12% of the patients, while 23% had elevations of either AP or ALT or both. Of the foregoing parameters, GGT was the best single indicator of liver involvement. In course of the follow-ups GGT/ALT correlation improved, but GGT/AP correlation deteriorated. In 9 patients, abstinence during follow-up was associated with progressive decrease in previously elevated serum GGT. Because of its unique sensitivity, GGT may be useful as a screening and/or monitoring aid in alcoholism.     

Oxidation-reduction potential dependence of low-temperature photoreactions of chloroplast Photosystem II

The light-induced free-radical signal of Photosystem II (observed after illumination at 77 °K) has been studied in chloroplasts as a function of the oxidation-reduction potential established prior to freezing. The intensity of the light-induced signal is unchanged in the potential region of +590 mV to +760 mV. At higher potential (+850 mV), there is a 30% decrease in signal intensity. The light-induced signal decreases to zero in the low-potential region, with a midpoint potential of +475 mV. These results are considered in terms of a Photosystem II reaction-center complex in which the light-induced free-radical signal arises from the oxidized form of the reaction-center chlorophyll, and this chlorophyll molecule is capable of being reduced at liquid-nitrogen temperature by a secondary electron donor which has a midpoint oxidation-reduction potential of +475 mV.     

Ribosomal protein S12 as a site for streptomycin resistance in Nicotiana chloroplasts

Summary A streptomycin resistant Nicotiana plastome mutant, X/str ^R6, was subjected to molecular analysis. In this mutant, a single nucleotide transition, C » T, in the chloroplast gene for ribosomal protein S12 alters codon 90 from proline to serine while the nucleotide sequence of the chloroplast 16 S rRNA gene is identical to that of the wild type. Mutant X/str ^R6 thus differs from several previously reported streptomycin resistant chloroplast mutants which are altered in the gene for 16 S rRNA.     

Weather- and population density-induced infantilism in the landsnailTheba pisana in a semi-arid climate

Natural populations of the landsnailTheba pisana (Pulmonata: Helicidae) were studied in the Mediterranean coastal plains of Israel. The life cycle is annual. Egg-laying occurs in the winter and the descendants grow fast during the spring, except for a part of the population the ceases growing. These individuals, termed infantiles, retain immature size and shape and a rudimentary status of the genital system. The percentage of infantilism in the population is positively related to the density of the snail population in the winter, and is negatively related to the humidity of weather in the spring. A natural control mechanism ofT. pisana populations is proposed: (a) in a dense population of young snails infantilism prevents most of them from becoming parents and an over-sized population the following year; (b) in a humid spring a fall in the rate of infantilism enlarges the population size, thus compensating for reduced egg-laying in winter.     

Calcium mobilizing hormones activate the plasma membrane Ca2+ pump of pancreatic acinar cells

Summary ⁴⁵Ca fluxes and free-cytosolic Ca²⁺ ([Ca²⁺] _i ) measurements were used to study the effect of Ca²⁺-mobilizing hormones on plasma membrane Ca²⁺ permeability and the plasma membrane Ca²⁺ pump of pancreatic acinar cells. We showed before (Pandol, S.J., et al., 1987.J. Biol. Chem. 262:16963–16968) that hormone stimulation of pancreatic acinar cells activated a plasma membrane Ca²⁺ entry pathway, which remains activated for as long as the intracellular stores are not loaded with Ca²⁺. In the present study, we show that activation of this pathway increases the plasma membrane Ca²⁺ permeability by approximately sevenfold. Despite that, the cells reduce [Ca²⁺]i back to near resting levels. To compensate for the increased plasma membrane Ca²⁺ permeability, a plasma membrane Ca²⁺ efflux mechanism is also activated by the hormones. This mechanism is likely to be the plasma membrane Ca²⁺ pump. Activation of the plasma membrane Ca²⁺ pump by the hormones is time dependent and 1.5–2 min of cell stimulation are required for maximal Ca²⁺ pump activation. From the effect of protein kinase inhibitors on hormone-mediated activation of the pump and the effect of the phorbol ester 12-0-tetradecanoyl phorbol, 13-acetate (TPA) on plasma membrane Ca⁺ efflux, it is suggested that stimulation of protein kinase C is required for the hormone-dependent activation of the plasma membrane Ca²⁺ pump.     

Interaction of plastocyanin with photosystem I: a chemical cross-linking study of the polypeptide that binds plastocyanin

Plastocyanin has been covalently cross-linked to photosystem I (PSI) by using a water-soluble cross-linker, N-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. The cross-linking reaction is light stimulated and results in the disappearance of a single 19-kDa subunit of PSI with the formation of a new protein-staining component of 31 kDa. The new product at 31 kDa reacts with both plastocyanin and 19-kDa subunit antibodies. Carboxyl group modified plastocyanin does not form a cross-linked product with PSI, implying that the negatively charged surface-exposed groups on plastocyanin are necessary to stabilize binding. These results demonstrate a specific interaction of plastocyanin with PSI and further implicate a specific protein to which plastocyanin binds to facilitate electron transfer to the P700 reaction center.     

Topography of the Protein Complexes of the Chloroplast Thylakoid Membrane : Studies of Photosystem II using Pronase Digestion and Chemical Labeling

The accessibility of various Photosystem II (PSII)-associated polypeptides to the protease pronase and the chemical modifier trinitrobenzene-sulfonic acid (TNBS) has been investigated. Three polypeptides with apparent molecular weight of 32, 21, and 16 kilodaltons, known to be associated with O₂ evolution, are all resistant to pronase digestion and TNBS labeling in intact thylakoids. All the polypeptides in the isolated PSII preparation were labeled with TNBS while a different pattern of labeling was observed when the PSII complex was isolated from TNBS-modified thylakoids. Attempts to prepare PSII particles from pronase-treated thylakoids using the Triton X-100 solubilization method were unsuccessful. Pronase-treated thylakoids were probed with antisera against the chlorophyll proteins of PSII using immunoblotting techniques. This allowed for a positive identification of proteolytic fragments from the respective proteins. The results are discussed in relation to the transmembrane organization of PSII in spinach thylakoids.     

Adaptation and growth of tomato cells on the herbicide 2,6-dichlorobenzonitrile leads to production of unique cell walls virtually lacking a cellulose-xyloglucan network

Suspension-cultured cells of tomato (Lycopersicon esculentum VF 36) have been adapted to growth on high concentrations of 2,6-dichlorobenzonitrile, an herbicide which inhibits cellulose biosynthesis. The mechanism of adaptation appears to rest largely on the ability of these cells to divide and expand in the virtual absence of a cellulose-xyloglucan network. Walls of adapted cells growing on 2,6-dichlorobenzonitrile also differ from nonadapted cells by having reduced levels of hydroxyproline in protein, both in bound and salt-elutable form, and in having a much higher proportion of homogalacturonan and rhamnogalacturonan-like polymers. Most of these latter polymers are apparently cross-linked in the wall via phenolic-ester and/or phenolic ether linkages, and these polymers appear to represent the major load-bearing network in these unusual cell walls. The surprising finding that plant cells can survive in the virtual absence of a major load-bearing network in their primary cell walls indicates that plants possess remarkable flexibility for tolerating changes in wall composition.