Metabolic regulation of the glucose-6-phosphate dehydrogenase from Paracoccus denitrificans grown on glucose/nitrate

Glucose-6-phosphate dehydrogenase (d-glucose-6-phosphate: NADP⁺ l-oxidoreductase EC 1.1.1.49) isolated from Paracoccus denitrificans grown on glucose/nitrate exhibits both NAD⁺-and NADP⁺-linked activities. Both activities have a pH optimum of pH 9.6 (Glycine/NaOH buffer) and neither demonstrates a Mg²⁺ requirement. Kinetics for both NAD(P)⁺ and glucose-6-phosphate were investigated. Phosphoenolpyruvate inhibits both activities in a competitive manner with respect to glucose-6-phosphate. ATP inhibits the NAD⁺-linked activity competitively with respect to glucose-6-phosphate but has no effect on the NADP⁺-linked activity. Neither of the two activities are inhibited by 100 M NADH but both are inhibited by NADPH. The NAD⁺-linked activity is far more sensitive to inhibition by NADPH than the NADP⁺-linked activity.     

Enzymic reconstitution of photosynthetic carbon assimilation. Pentose phosphate-dependent O evolution by illuminated envelope-free chloroplasts from Spinacia oleracea.

The ability of envelope-free spinach chloroplasts to carry out self-sufficient CO₂-dependent O₂ evolution at rapid rates has recently been made possible by the appropriate addition of cofactors, coenzymes, unfractionated stromal protein, and purified ferredoxin. Comparable enzymic reconstitution is now reported in which photosynthetic oxygen evolution depends upon the presence of ribose 5-phosphate and purified protein fractions which collectively catalyze its conversion to glyceraldehyde 3-phosphate. The levels of these enzymes (phosphoriboisomerase, phosphoribulokinase, ribulose-1,5-bisphosphate carboxylase, 3-phosphoglycerate kinase and NADP-specific triose phosphate dehydrogenase) in intact spinach chloroplasts have also been measured and all but that of 3-phosphoglycerate kinase shown to be substantially higher than those originally reported for the parent tissue. The results are discussed in their relation to the feasibility of complete enzymic reconstitution of carbon assimilation in a chloroplast system capable of normal rates of photosynthesis and its possible role in future evaluation of photosynthetic regulation.     

Ultrastructural and biochemical characterization of the epidermal hairs of the seeds of Cuphea procumbens

Rehydration of desiccated Cuphea seeds results in a rapid morphological change in the seed. Within 20 min thread like epidermal hairs are present on the seed surface. The hairs, which are highly ordered helical structures, are present in the epidermal cells of the desiccated seed. Following emergence the hairs increase in length by means of an eversion process, the mechanism for which is proposed in the text. The hairs were purified to homogeneity and found to be composed of 55% carbohydrate and 45% protein. Following -elimination of the carbohydrate using NaOH/NaBH₄ one major protein of MW 31,000 was seen upon polacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. The protein, here termed helexin, probably plays a major structural role in determining the helical shape of the hairs.     

Plant glycerol-3-phosphate-1-acyltransferase (GPAT): structure selectivity studies

Squash glycerol-3-phosphate-1-acyltransferase has been crystallized and the structure of the enzyme determined, at 1.9-A resolution, using multiple isomorphous replacement of the wild type and a series of individual cysteine mutants. Competitive in vitro substrate selectivity assays have been established that differentiate between selective and non-selective forms of the enzyme. Particular care was taken to use near-physiological concentrations of both substrates. Clear substrate selectivity can be demonstrated with the natural substrate acyl-acyl carrier protein but not with the substrate analogue acyl-CoA. The use of site-directed mutagenesis, coupled to three-dimensional structural determinations, should provide a rational basis for elucidating structural components important in determining the substrate selectivity of this enzyme.     

Limnanthes douglasii erucic acid-specific lysophospatidic acid acyltransferase activity in oilseed rape: an analysis of biochemical effects

It has been shown previously that erucic acid accumulates in the sn-2 position of triglycerides after introduction of a Limnanthes lysophosphatidic acid acyltransferase. However, in none of the studies to date has a proper evaluation been made of the relationship between transgene expression and the erucic acid accumulation at sn-2. One of the necessary tools to study the variability is the presence of a specific antibody raised against the introduced acyltransferase. In the present study, we have looked at the correlation between erucic acid accumulation at sn-2, production of trierucin and the expression of the transgene, as detected by Western blotting. The data presented include comparisons of progeny of individual lines grown under various conditions and at various times, and an analysis of a number of lines during development. We also present calculations that could indicate from which position the erucic acid found at position sn-2 is derived.     

Radiographic joint damage in rheumatoid arthritis is associated with differences in cartilage turnover and can be predicted by serum biomarkers: an evaluation from 1 to 4 years after diagnosis

Introduction  

The objective of this study was to determine whether serum biomarkers for degradation and synthesis of the extracellular matrix of cartilage are associated with, and can predict, radiographic damage in patients with rheumatoid arthritis (RA).     

Retinitis pigmentosa: rapid neurodegeneration is governed by slow cell death mechanisms

For most neurodegenerative diseases the precise duration of an individual cell''s death is unknown, which is an obstacle when counteractive measures are being considered. To address this, we used the rd1 mouse model for retinal neurodegeneration, characterized by phosphodiesterase-6 (PDE6) dysfunction and photoreceptor death triggered by high cyclic guanosine-mono-phosphate (cGMP) levels. Using cellular data on cGMP accumulation, cell death, and survival, we created mathematical models to simulate the temporal development of the degeneration. We validated model predictions using organotypic retinal explant cultures derived from wild-type animals and exposed to the selective PDE6 inhibitor zaprinast. Together, photoreceptor data and modeling for the first time delineated three major cell death phases in a complex neuronal tissue: (1) initiation, taking up to 36 h, (2) execution, lasting another 40 h, and finally (3) clearance, lasting about 7 h. Surprisingly, photoreceptor neurodegeneration was noticeably slower than necrosis or apoptosis, suggesting a different mechanism of death for these neurons.