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The metabolism of carbohydrates in guayule is a subject which has not been considered with respect to its role in cis-polyisoprene synthesis, It has been suggested that acetate or sucrose act as the distal, and isopentenylpyrophosphate as the immediate precursor of the isoprenoid biosynthetic pathway. Application of radioactive precursors to the leaves of guayule plants in Winter and Summer showed that the fate of the carbohydrate depends on the chemical structure of the carbohydrate and the time of application. [[14]C] Sucrose was incorporated into the acetone (resin) fraction during the Summer and petroleum ether (rubber) fraction during the Winter. The amount of radioactivity that was translocated in Winter and Summer was similar. The loss of leaves during Winter reduced the area for photosynthesis, while the loss of carbon from the leaves during Summer, probably due to photorespiration, decreased the amount of available photosynthates. These two phenomena did not disadvantage the plant as far as the allocation of carbon was concerned. No plant components were acting as sinks during the Winter. The pith of the crown area incorporated the most radioactivity in Summer. [[14]C] Fructose was more readily translocated than [[14]C] sucrose during a 12 hour experiment. When fructose was applied and plants were left for 48 hours, more radioactivity was translocated to the stems and roots during the Summer. The [[14]C] from fructose was incorporated into the acetone (resins) rather than the petroleum ether (rubber) fraction in Winter therefore apparently having a different fate to [[14]C] sucrose. The principal reserve carbohydrates in guayule are fructans. Two types of fructans were detected and are referred to as water-soluble or ethanol-soluble fructans. The ethanol-soluble fructan polymers apparently played an active role in metabolism of guayule and showed cyclic patterns of accumulation. The water-soluble fructans seem to be true reserve carbohydrates, depolymerizing when the carbon supply decreased at the end of Winter, and the demand for carbon increased at the inception of bud break. Fructans provide carbon for budbreak and exposure of plants to longer days and higher temperatures did not seem to alter this role. It is proposed that fructans are providing carbon for budbreak and renewed growth and are utilized for flowering when required. Starch production occurs during the warmer months in the leaves and young stems. Starch is synthesized from the immediate photosynthetic supply and it is this source of carbon which is utilized for the synthesis of cis-polyisoprene (rubber). Sucrose in the cytosol is sequestered for cis-polyisoprene synthesis while fructose, which can enter the plastid, is providing carbon for the synthesis of isoprenoids. Compartmentation of resin and rubber production ensures that the supply of carbon is adequate for both processes. As cis-polyisoprene synthesis occurs at a time when the plant is not disadvantaged by insufficient carbon , induction of rubber transferase enzymes would not depend on excess substrate, but would use a more reliable cue like temperature or daylength. Any attempt therefore to increase the carbon supply in guayule during the winter months would not necessarily lead to partitioning into cis-polyisoprene, but may be stored as fructan to ensure that, at bud break, the plant has an adequate and utilizable carbon supply. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

In an effort to determine the effects of carbohydrate feedings on exercise performance, ten male subjects performed intermittent exercise on an electrically braked cycle ergometer for a total of four hours. At the end of the four hours exercise, subjects performed a timed sprint ride to exhaustion. During the experimental trial, subjects ingested a total 172 g of solid carbohydrate. Repeated carbohydrate feedings improved the time to exhaustion at the end of the exercise, and consequently produced higher blood lactate levels. During the exercise, less muscle glycogen was used with carbohydrate feedings. Carbohydrate feedings, therefore, spare muscle glycogen during endurance exercise and improve sprint performance at the end of such exercise bouts.

Clostridium perfringens was found to produce marked changes in its environment during growth. Decrease in electropotential, as well as decrease in pH, correlated with resumption of cellular activity on transfer into a defined medium. Eight amino acids were found to be essential for growth, while the remaining ten amino acids fell into four categories according to the degree of independence the organism had with respect to them. The form of the B-6 vitamin present in the medium had an important influence on the synthesis of several amino acids. The synthesis and degradation of amino acids was investigated further. The enzyme systems involved in these functions could be described as three major groups: those enzymes involved in synthesis of amino acids and amino compounds from glucose, the enzymes responsible for the interconversion of threonine, glycine and serine, and those involved with glutamic acid, proline and arginine metabolism. Uptake of amino acids by both resting and growing cell suspensions was found to be by an efficient, non-energy dependent diffusion mechanism. During growth approximately 5% of the exogenously supplied glucose was assimilated into cell material, primarily as cell wall or nucleic acid components. Molar growth yields from glucose were found to be significantly greater than the theoretical value. The calculated ratio of reduced to oxidized coenzymes indicated a characteristic trend over the logarithmic and stationary growth phases. The relationship between amino acid metabolism, glucose dissimilation and assimilation, and overall metabolite and energy balances has been discussed with a view to understanding the extent of control and influence C. perfringens has on its own metabolic functions and on its environment. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

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The study was designed to indirectly understand muscle glycogen utilization during prolonged exercise when either glucose, fructose, or water is ingested. Eight trained adult males exercised on a cycle ergometer at 58±7% of V02 max for 2 h on 2-4 occasions. At 0 minutes of exercise and at 30-minute intervals throughout the exercise, the subjects ingested 200mL of fluid containing either glucose, fructose, or plain water in a double-blind, randomized fashion. The carbohydrate (CHO) fluid concentration was based on each subject's body weight (BW): Ig CHO X kg⁻¹ BW X L⁻¹ water and ranged from 5.8-9.2% (average=7.5%) of BW. Blood samples were collected from subjects at rest and immediately prior to fluid ingestion during exercise and analyzed for hematocrit, hemoglobin, and plasma levels of glucose, lactate, and pyridoxal 5'-phosphate (PLP). ANOVA showed no significant difference among treatments at any time of exercise for mean plasma lactate and PLP levels (p > 0.05). Although not significant, mean plasma lactate and PLP concentrations tended to be lower when glucose was consumed as compared to fructose and water. The mean plasma glucose level, however, uas significantly different among treatments at specific time points of exercise (p < 0.05). During exercise, mean plasma glucose decreased, and there was a higher plasma glucose level when glucose and fructose fluids were ingested as compared to water. At 60 minutes of exercise, this difference uas evident for both glucose and fructose ingestion (p < 0.05). At 90 and 120 minutes of exercise, fructose ingestion produced a significantly higher mean plasma glucose level than either water or glucose ingestion (p < 0.05). It is hypothesized that the higher plasma glucose levels provided a greater blood glucose supply to working muscles, thereby sparing muscle glycogen stores. The findings indicate that for the long-term exerciser, consumption of a 5.8-9.2% fructose solution may promote less muscle glycogen utilization than either glucose or water, thereby possibly increasing endurance. / Graduation date: 1986

Exercise performance was examined after ingestion of 45 g of liquid carbohydrate (LCHO), solid carbohydrate (SCHO), or water (W) 5 min before 1 h of intense exercise.An (CHO) meal (200 g) taken 4 h prior to exercise was combined with a solid CHO feeding (M+SCHO). Ten well-trained male cyclists (4.35 + 0.11 1/min V02 max) performed 45 min of cycling at a work load requiring an average oxygen uptake of 77.1% V02 max followed by a 15 min performance ride. Serum glucose values were elevated by 18% and 24% during SCHO and LCHO, respectively, as compared to W. Blood glycerol concentrations were significantly (p<0.05) lower during M+SCHO and significantly higher during W at 40, 50 and 60 min of exercise as compared to all other trials. Muscle biopsies at 0 and 45 min revealed no significant differences in muscle glycogen concentration or total use between the 4 trials. Total work produced during the final 15 min of exercise was significantly greater during M+SCHO (194735 + 9448 NM) as compared to all other trials and significantly greater during LCHO and SCHO (175204 + 11780 and 176013 + 10465 NM, respectively) as compared to W (159143 + 11407 NM). Carbohydrate oxidation was highly correlated (r=0.94) with work production. These results suggest that exercise performance is enhanced with the ingestion of 45 g of CHO 5 min prior to one hour of intense cycling. Further improvements in performance were found when exercise was preceded by a CHO meal 4 h prior to exercise in combination with a solid CHO feeding given immediately before exercise.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

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