Colestipol-induced changes in LDL composition and metabolism. II. Studies in humans.

We investigated the effect of the bile acid sequestrant, colestipol hydrochloride, on the composition and metabolism of human low density lipoprotein (LDL). Colestipol treatment produced a disproportionate decrease in LDL cholesterol compared to LDL apoB, resulting in a significant decrease in the LDL cholesterol/apoB ratio. Electron microscopy revealed that LDL particles were smaller in size and analytical ultracentrifugation demonstrated that colestipol therapy selectively depleted larger, more buoyant LDL particles of Sf degrees 6-7. Thus, colestipol therapy produced LDL that were smaller in size, more dense, and characterized by a decreased cholesterol to protein ratio. To determine whether the altered LDL had different metabolic properties, autologous LDL was isolated from subjects before and during colestipol therapy and their fractional catabolic rates (FCR) were then simultaneously determined in the same patient while on therapy. Eight LDL turnover studies comparing the catabolism of LDL isolated during therapy (Rx-LDL) and LDL isolated off therapy (Con-LDL) were performed in six subjects. All subjects responded to colestipol treatment, with an average 29% fall in LDL cholesterol. In four of six subjects, and in six of eight studies, the FCR of Rx-LDL was substantially slower than that of Con-LDL. These studies demonstrate that a drug intervention may alter subpopulations of LDL particles in such a way that overall LDL composition is changed. This alteration may independently affect the intrinsic metabolic behavior of the LDL. We suggest that such drug- (or dietary-) induced changes in LDL composition need to be considered in kinetic studies designed to assess the overall impact of the perturbation being studied.

The photosynthetic response to a shift in the chlorophyll a to chlorophyll B ratio of chlorella.

The chlorophyll a:b ratio was shifted in Chlorella vannielii by varying the illuminance under which the cells were cultured-the ratio increased from 2.9, 3.0, 4.0, and 4.8 to 6.2, respectively, at 100, 300, 900, 2,700 and 6,000 foot candles. The 6,000-foot candle cells retained an optimal growth rate at the chlorophyll a:b ratio of 6.2 which was the upper limit of normal growth. Comparisons were made between the 300-and 6,000-foot candle cultures to determine the significance to the photosynthetic mechanism of a shift in the chlorophyll a:b ratio.The high light cells (6,000 foot candles) contained only one-tenth the total amount of chlorophyll of the low light cells (300 foot candles) based on dry weight. The total chlorophyll per cell of the high light cells was one-fifth of that in the low light cells. Electron micrographs indicated differences in chloroplast structure. An average of five or six thylakoids composed a granum-like region of the low light chloroplasts, whereas only a pair of thylakoids at most was found in the high light chloroplasts. The high light chloroplasts had more starch. On a dry weight basis, the high light cells had a respiration rate 3 times that of the low light cells. Based on chlorophyll, the respiration rate of the high light cells was 26 times greater. Based on dry weight, the oxygen evolution for both cultures was essentially the same at 6,000 foot candles; however, at 300 foot candles the rate for the low light cells was about 5 times faster than that of the high light cells. With chlorophyll as the index, the rates of the high light cells were higher than those of the low light cells-7 times faster at 6,000 and 2 times faster at 300 foot candles. At 10,000 foot candles, the low light-grown cells underwent photooxidation, whereas the high light grown cells photosynthesized at a rate slightly higher than at 6,000 foot candles.Action spectra of system II (oxygen evolution) from a modulated polarograph indicated photochemical participation of chlorophyll b in the high light deficient cells, although the participation was much less than in the low light cells. Enhancement was 1.11 for the low light cells, and 1.05 for the high light cells.In order to account for the energy balance in the two cultures it was concluded that perhaps oxidative phosphorylation supplemented a reduced photophosphorylation in the high light cells. Experiments with peroxyacetyl nitrate support the view that cyclic photophosphorylation is less in the chlorophyll b-deficient cells. Chlorophyll b served also to broaden absorption for the photosynthetic unit-a detrimental role when cells are illuminated above saturation.

FACTORS AFFECTING THE RATE OF CALCIFICATION IN HALIMEDA OPUNTIA (L.) LAMOUROUX AND HALIMEDA DISCOIDEA DECAISNE(1).

Halimeda is a prominent part of the calcifying algae in the coral-reef lagoon ecosystems in the Caribbean. Experiments were performed on the Cayo Enrique Reef off Puerto Rico and in the laboratories of the University of Maryland to study factors influencing the calcification processes. Halimeda opuntia has a higher percentage of calcium carbonate than does Halimeda discoidea and a faster rate of incorporation. Halimeda opuntia and Halimeda discoidea show a stimulation of incorporation by light as well as a diurnal rhythm under identical conditions of illumination. Both phenomena parallel the rhythm of chloroplast migration within the plant. Calcification is also stimulated by the addition of carbon dioxide. Such evidence clearly indicated a light-linked mechanism which could involve photo-synthesis. However other metabolic processes, such as respiration, are also implicated. Aeration alone accelerates calcium incorporation. Nitrogen sources inhibit the incorporation of calcium during the day, indicating that cellular ammonia production is probably not responsible for precipitation. The differential wash-out rates of calcium absorbed during the day compared to those at night support the concept of a 2-step mechanism for calcification.

Responses of Heterotrophic Cultures of Chlorella vulgaris Beyerinck to Darkness and Light. I. Pigment and pH Changes.

Glucose cultures of Chlorella vulgaris were grown in white light, in monochromatic light, and in darkness. Difference spectra showed that all wavelengths resulted in increased pigmentation over the dark controls.Cells irradiated with the 600 mmu beam showed a much higher absorption in the blue end of the spectrum with respect to the red end than is normally found in absorption spectra of white-light grown Chlorella cells.Dry weight comparisons between monochromatic light and dark controls showed the controls to be somewhat higher. This demonstrated that the monochromatic irradiation produced pigment synthesis but no increase in growth. Dark growth experiments suggested that cultures incubated in darkness on glucose excreted an acidic product.

Responses of Heterotrophic Cultures of Chlorella vulgaris Beyerinck to Darkness and Light. II. Action Spectrum for and Mechanism of the Light Requirement for Heterotrophic Growth.

Chlorella vulgaris Beyerinck (Emerson's strain), fails to grow in the dark even when sugars are provided. This phenomenon was clearly demonstrated in the alga, C. vulgaris, for which the growth rate in darkness on a glucose medium remained constant for 2 days and then declined to approach zero. Pigment concentrations also declined in darkness. Changes in flow rate of 1% CO(2)-in-air from zero to 7 ml per minute caused a progressive increase in the dark growth rate over a 5-day period, but did not maintain growth in the dark. Rates above 7 ml per minute produced no changes in growth rates.White light intensities below the compensation point of the alga maintained heterotrophic growth. The saturation value for this response was 0.8 muw/cm(2). White light also initiated growth in nongrowing cultures transferred from darkness to light.The action spectrum for heterotrophic growth indicated a porphyrin as the active pigment. Light in the 425 mmu region was 4 times as effective as white light in stimulating heterotrophic growth. A secondary peak of growth stimulation occurred in the 575 mmu region.The respiration of glucose by the alga was stimulated by low intensities of white light. This response was not immediate, but was clearly present after the third day of incubation.Malonate and cyanide were inhibitory to growth of C. vulgaris on inorganic medium or glucose medium under 300 ft-c of white light. These data suggested that succinic dehydrogenase and cytochrome oxidase systems were present.Substances inhibitory to growth were excreted into the medium under dark-growth conditions, and 2 of these substances were indentified as formic and acetic acids.The evidence suggested that respiration of glucose cannot proceed for an extended period of time in darkness. The reason for this is postulated to be the lack of a cytochrome or a cytochrome precursor.