The pyruvate dehydrogenase complex has been purified 76-fold, to a specific activity of0.6 umoles per minute per milligram protein, beginning with isolated pea (Pisum sativum L. var Little Marvel) chloroplasts. Purification was accomplished by rate zonal sedimentation, polyethyleneglycol precipitation, and ethyl-agarose affinity chromatography. Characterization of the substrates as pyruvate, NAD', and coenzyme-A and the products as NADH, C02, and acetyl-CoA, in a 1:1:1 stoichiometry unequivocally established that activity was the result of the pyruvate dehydrogenase complex. Immunochemical analysis demonstrated significant differences in structure and organization between the chloroplast pyruvate dehydrogenase complex and the more thoroughly characterized mitochondrial complex. Chloroplast complex has a higher magnesium requirement and a more alkaline pH optimum than mitochondrial complex, and these properties are consistent with light-mediated regulation in vivo. The chloroplast pyruvate dehydrogenase complex is not, however, regulated by ATP-dependent inactivation. The properties and subcellular localization of the chloroplast pyruvate dehydrogenase complex are consistent with its role of providing acetyl-CoA and NADH for fatty acid synthesis.The pyruvate dehydrogenase complex is a multicomponent system composed ofthe three enzymes, pyruvate dehydrogenase, dihydrolipoyl transacetylase, and dihydrolipoyl dehydrogenase. The (11,15,16). Phosphorylation (inactivation) of pyruvate dehydrogenase is catalyzed by a tightly associated kinase and dephosphorylation (activation) by a more loosely associated phosphatase (10).The pivotal position of PDC in metabolism has resulted in a vast amount of research on the enzyme from nonplant tissues. By comparison, relatively little is known about plant PDC, and most information that is available concerns the mitochondrial form of the enzyme. The limited knowledge of plastid PDC prompted the current investigation with the purpose ofestablishing the chloroplast enzyme as a true PDC with properties distinct from the mitochondrial enzyme and consistent with its postulated role in chloroplast fatty acid biosynthesis.

Changes in activities of photosynthetic enzymes and photochemical processes were followed with aging of vegetative and flag leaves of wheat (Triticum aestivum L. cv Roy). Activities of stromal enzymes began to decline prior to photochemical activities. In general, total soluble protein and the activities of ribulose-1,5-bisphosphate carboxylase and NADPtriose-phosphate dehydrogenase decUned in parallel and at an earlier age than leaf chlorophyll (Chl), leaf photosynthesis, and photosynthetic electron transport activity. Leaves (8) in Phaseolus vulgaris L. observed a continual decline in electron transport per mg Chl, which suggested a gradual degradation of -all chloroplasts. Studies of electron transport as well as other physiological parameters are needed before definitive conclusions can be made as to the loss of whole chloroplasts from wheat leaves.In the present study, the time course of leaf development from full expansion through senescence was investigated in vegetative and flag leaves of wheat to determine the basis for reduction of photosynthesis. Specific objectives of this study were to determine (a) if electron transport activities or stromal enzyme activities declined first and (b) if there was a general decline in the photosynthetic functioning of all chloroplasts or if there was a preferential degradation of whole chloroplasts.Senescence is a coordinated, deteriorative growth process that is initiated at full maturity and ultimately leads to the death of a cell, organ, or organism. To characterize a tissue that is undergoing senescence, it is necessary to identify the sequential order in which various parameters change. Butler and Simon (5) reported from ultrastructural studies that aging is first expressed in the chloroplast. Thus, changes in the physiology of this organelle are important to our understanding of senescence.In leaves, senescence is typically characterized by a decline in MATERIALS AND METHODS Plant Material. Triticum aestivum L. cv Roy was grown in a growth chamber with a photon fluence rate of 3 x 1 -O mol/m2. s (400-700 nm) and a 15-h photoperiod (22°C day/17°C night). For vegetative leaves, the second leaf to emerge was studied from the time of full expansion (about 14 d from planting) through senescence. Flag leaves were sampled from the point of emergence of the head from its sheath (arbitrarily designated day 0) through senescence. Flag leaves were fully expanded at this stage. Reproductive development was induced by vernalization of 12-d-old seedlings for 6 weeks at 2 to 4°C. All plants were fertilized twice weekly with Hoagland solution.Two separate plantings of both vegetative and flag leaf material were used. Two to four replications of each parameter for each age were performed and the results from both plantings were averaged.Leaf Area, Chi, and Protein Assays. Leaf area was measured with a Li-Cor3 area meter (model LI-3000, Li-Cor, Inc.). Chl and Chl a/b ratios were determined by the procedure of Arnon (1).

The ability of oral Streptococcus strains to utilize oligosaccharide chains in mucin as a source of carbohydrate was studied in batch cultures. Pig gastric mucin, as a substitute of human salivary mucin, was added to chemically defined medium containing no other carbohydrates. Strains of S. mitior attained the highest cell density, while mutans streptococci: S. mutans, S. sobrinus, S. rattus, grew very little in the medium with mucin. S. mitis, S. sanguis, and S. milleri in decreasing order, showed intermediate growth. Mucin breakdown as measured by sugar analyses indicated that oligosaccharide chains were only partially degraded. Every strain produced one or more exoglycosidases potentially involved in hydrolysis of oligosaccharide. The enzyme activities occurred mainly associated with the cells, and very little activity was found in the culture fluids. The relationships between glycosidase activities and growth, or mucin degradation were not always clear.

Oral streptococci can grow in mucin by utilizing the oligosaccharide chains as a source of carbohydrate. The degradation of the oligosaccharides by these species is accomplished by exoglycosidase activities. In this experiment, it was investigated whether strains from different species could cooperate in the release of sugars from the mucin oligosaccharide. To this end, Streptococcus sanguis Ny 584 and Streptococcus oralis strain Ny 586 were grown continuously in a chemically-defined medium, with pig gastric mucin as the growth-limiting source of carbohydrate. In pure cultures, strain Ny 586 attained approximately three-fold-higher cell densities than did strain Ny 584 in the mucin medium. This was in accordance with the observation that S. oralis Ny 586 exhibited fucosidase activity, as indicated by the presence of fucose in the culture fluid. In contrast, strain Ny 584 has no fucosidase activity against mucin, and therefore cannot attack fucose-ending oligosaccharide chains. Stable mixed cultures of the strains were obtained. It appeared that S. sanguis Ny 584 reached significantly higher cell densities in mixed cultures with S. oralis Ny 586 than in pure culture. Stimulation of the growth of strain Ny 584 was probably due to the generation of non-fucose-ending oligosaccharide chains by fucosidase from strain Ny 586. It is concluded that the synergistic degradation of oligosaccharides in glycoproteins is a potential factor influencing the streptococcal populations in the mouth.

Oral Streptococcus species experience carbohydrate limitation interrupted by periods of substrate excess following food intake by the host. To investigate the competitiveness of various streptococcal species under fluctuating carbohydrate supply, 2-membered chemostat cultures were run.Under continuous limitation of glucose or sucrose, all 6 Streptococcus mutans test strains were outcompeted by Streptococcus sanguis P4A7 or Streptococcus milleri B448. This indicated that S. mutans had a lower affinity for glucose and sucrose than S. sanguis and S. milleri.Mixed cultures were then subjected to hourly pulses with glucose. Under these conditions S. mutans Ny344 competed successfully with S. milleri B448, but still lost the competition against S. sanguis P4A7. The streptococci responded to pulses by taking up glucose at the maximum rate almost instantaneously. S. sanguis P4A7 had the highest rate of glucose uptake while the qmax value of S. mutans Ny344 was higher than that Of S. milleri B448. This suggested a causal relationship between qmax and competitiveness.