Transfer of reducing equivalents into mitochondria by the interconversions of proline and Δ1-pyrroline-5-carboxylate

Direct evidence is presented for a proline cycle using a cell-free experimental system which sequentially transfers ³H from [1-³H]glucose to NADP⁺ to Δ¹-pyrroline-5-carboxylate and yields [³H]proline. The formation of [³H]proline depends on the presence of NADP, Δ¹-pyrroline-5-carboxylate, and the enzymes glucose-6-phosphate dehydrogenase and Δ¹-pyrroline-5-carboxylate reductase. The production of [³H]proline from unlabeled proline in the presence of mitochondria provides direct evidence for one complete turn of a proline cycle which transfers reducing equivalents produced by glucose oxidation in the pentose pathway into mitochondria. In this cycle, proline is oxidized to Δ¹-pyrroline-5-carboxylate by mitochondrial proline oxidase. Δ¹-pyrroline-5-carboxylate is released from mitochondria and is recycled back to proline by Δ¹-pyrroline-5-carboxylate reductase with concomitant oxidation of NADPH. At the maximal rate observed, 60% of Δ¹-pyrroline-5-carboxylate produced is recycled back to proline. This cycle provides a mechanism for transferring reducing equivalents from NADPH into mitochondria and is linked to glucose oxidation in the pentose pathway by NADPH turnover.     

Stimulation of the hexose-monophosphate pentose pathway by delta 1-pyrroline-5-carboxylic acid in human fibroblasts.

L-pyrroline-5-carboxylic acid, an intermediate in the interconversions of glutamic acid, ornithine and proline, is a potent stimulator of the hexose-monophosphate pentose pathway in cultured human fibroblasts. These studies suggest that pyrroline-5-carboxylate reductase, which catalyzes the conversion of pyrroline-5-carboxylate to proline coupled with the oxidation of NADPH, provides the NADP for the observed activation of the hexose-monophosphate pentose pathway.     

Polygalacturonase activity and variation in ripening of papaya fruit with tissue depth and heat treatment

Effects of tissue position (viz. outer vs inner mesocarp) and heat treatment (48°C, 20 min) on variations in polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activity and ripening of fruits of Carica papaya L. cv. Backcross Solo were investigated. Polygalacturonase activity increased during ripening concomitantly with an increase in tissue softness and soluble polyuronide level. Throughout ripening, inner mesocarp tissue was softer and contained higher polygalacturonase activity than outer mesocarp tissue. Titratable acidity as well as ß-galactosidase (EC 3.2.1.23) activity also increased during ripening; however, unlike polygalacturonase, their level or activity was lower in inner than in outer mesocarp. Ascorbic acid could partially account for the increase in titratable acidity during ripening but contributed very little to the differences in titratable acid levels between outer and inner mesocarp. Heat treatment had no effect on either fruit softness or titratable acidity, but it markedly reduced the increase in ascorbic acid and polygalacturonase activity during ripening. Ripening, as reflected by changes in tissue softness and polygalacturonase activity, progressed outwardly from the interior towards the exterior of the fruit. The effect of heat treatment in suppressing polygalacturonase activity was relatively greater in inner than in outer mesocarp, suggesting that sensitivity of the enzyme to heat treatment may vary with stage of ripeness of the tissue.     

Effects of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea on the Cell Cycle in Euglena gracilis

The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G₂/M. The specificity of this response and its relationship to photosynthesis was studied by looking at the effect of DCMU on dark grown wild-type cells, and on two bleached variants of Euglena (W₃BUL and W₁₀BSmL) that lack chloroplasts. The drug does block G₂/M in these cells, but not entrance into the cell cycle. Our studies show that entrance of cells into the cell cycle from a quiescent state does not require active photosynthesis, and that DCMU has effects on G₂/M transit that are independent of the photosynthetic capacity of the cells.     

Treatment of burn alopecia with tissue expanders in children

During the past 18 months, 60 tissue expanders were utilized in the reconstruction of 42 children with burn alopecia of the scalp not amenable to a single excision and primary closure at the Shriners Burns Institute in Galveston, Texas. The children were grouped according to the degree of alopecia. All patients with defects of 15 percent or less of the total hair-bearing scalp were able to obtain complete closure of their defects with two operations, i.e., one to place the expander and the second to remove the expander and advance the flaps. Some patients with defects up to 40 percent were closed with serial expansion. Patients with even larger defects had a significant reduction in the percentage of alopecia and benefited from re-creation of anterior hairlines. We have encountered a postoperative complication rate of 10 percent. When compared to previous methods of treating burn alopecia, tissue expansion allows a more rapid closure, fewer operations and coincident anesthetics, and decreased total length of hospitalization.     

The ontogeny of the vascular cambium inGinkgo biloba roots

Observation was made on early ontogeny of vascular cambium in the developing root ofGinkgo biloba L. After completion of root elongation, the vascular meristem gradually acquires cambial characteristics. Strips of the periclinal division of cells in transverse section are observed on the inner side of phloem when the primary xylem and phloem in the stele have been established. The strips are united into a continuous layer between phloem and xylem. In tangenital section, the procambium shows a homogeneous structure, which is initially composed of short cells with transverse end walls and subsequently, of long cells with tapering ends. Then, the procambium is organized into two systems of cells; axial strands of short cells with transverse end walls resulting from the sporadic transverse divisions of long cells, and long cells with tapering ends. Still later, the short cells are divided frequently in a trasverse plane exhibiting one or a few cells in width and several decades of cells in height, while the long cells are elongated. The frequency of transverse divisions of the short cells decreases in subsequent stages. Eventually, the short cells in axial strands are vertically separated from one another by the elongation of neighboring long cells and by the decrease in the frequency of transverse divisions of short cells themselves. Cambial initials occur in two forms; ray initials a few cells in height and one cell in width derived from the short cells, and fusiform initials with tapering ends derived from the long cells.