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Biomedical subjects

H E Clark

Publications and source records attributed to H E Clark.

At least 37 records · Page 2Linked to original sources

Nitrogen retention and plasma amino acids of men who consumed isonitrogenous diets containing egg albumen or mixtures of amino acids.

Experimental diets that furnished approximately 6.0 g of nitrogen per day were consumed by young men. Nitrogen retention was not altered significantly when egg albumen was replaced by its constituent essential and nonessential amino acids or by the essential amino acids (including cystine, tyrosine and histidine) plus a source of nonspecific nitrogen. Concentrations of essential amino acids in fasting or postprandial plasma were not influenced significantly by source of amino acids or by replacement of nonessential amino acids by nonspecific nitrogen; but concentrations of certain nonessential amino acids were altered by treatment. Responses to an elemental diet or to a similar diet in which egg albumen replaced the amino acid mixture did not differ significantly.

Adult↗

On the Role of Manganese in Photosynthesis: Kinetics of Photoinhibition in Manganese-deficent and 3-(4-Chlorophenyl)-1, 1-dimethylurea-inhibited Euglena gracilis.

Euglena gracilis (Klebs) cultures were grown under conditions where limitation in supply of manganese limited chlorophyll content much more than growth. Although the initial rates of photosynthetic oxygen evolution were not affected by the level of manganese, photoinhibition in high intensity light was markedly influenced. All cultures showed first order kinetics for photoinhibition, with the half-time exponentially related to the Mn concentration in the medium. Treatment with 3-(4-chlorophenyl)-1, 1-dimethylurea (CMU) also increased the rate of photoinhibition. Manganese-deficient cells were also more sensitive to CMU inhibition of photosynthesis. The similar effects on photoinhibition of manganese deficiency and of CMU treatment and the protective action of manganese against photoinhibition and CMU poisoning are interpreted to indicate a site of action of manganese on the reducing side of photosystem II, close to the CMU-sensitive site. This manganese-affected site may represent a secondary structural or metabolic consequence of manganese deficiency, not necessarily involved in quantum yields of oxygen.

Journal Article↗