Factors controlling the production of ethanol and lactate have been examined using cell free extracts prepared from pea seeds (Pisum sativum var Alaska) and parsnip roots (Pastinaca sativa). The result suggest that under aerobic conditions pyruvate decarboxylase is inactive. With the onset of anaerobiosis glycolysis leads to an accumulation of lactate with a corresponding fall in pH. The fall in pH activates pyruvate decarboxylase and initiates competition between lactate dehydrogenase and pyruvate decarboxylase for pyruvate. The effect of pyruvate concentration on the partitioning has been analysed in terms of a modified Wegscheider rule and shows that the ratio lactate dehydrogenase activity/pyruvate decarboxylase activity bears an inverse relationship to the pyruvate concentration. The decrease in ratio which occurs when the pyruvate concentration rises is enhanced by the co-operativity which is exhibited by pyruvate decarboxylase. The pH optimum of lactate dehydrogenase is alkaline whilst the pH optimum of pyruvic decarboxylase is acid, thus the two enzymes function as a pH-stat. The possibility of excessive production of lactic acid is further controlled by the response of lactate dehydrogenase to ATP; the enzyme is inhibited by ATP and the inhibition increases as the pH decreases. It is suggested that this mechanism functions to protect the plant from excess production of acid.
1. The stereospecificity of 20 enzymes from plants is reported. 2. The stereospecificity of all known forms of malate dehydrogenase in plants and animals has been shown to be A-specific. 3. The generalization that ;the stereospecificity of a particular reaction is independent of the source of the enzyme' is confirmed for a total of 12 plant enzymes. 4. A new generalization is proposed: ;When a metabolic sequence involves consecutive nicotinamide-adenine dinucleotide-dependent reactions, the dehydrogenases have the same stereospecificity.'
Pleural effusion fluid obtained from eleven patients with metastatic spread to the pleura was screened for the ability to cause the dispersal--'scattering'--of MDCK colonies in vitro. Four of these samples proved to be positive using this assay. Of these two had titres high enough to warrant further purification on a cation exchange Mono S column. Active material from both lung samples, eluted at the same positions as factor from cultured human lung fibroblasts (MRC-5) and human placenta but in a slightly different position to murine scatter factor. In both cases the semi-purified active agent was identified as hepatocyte growth factor/scatter factor (HGF/SF) using an ELISA detection system specific for human HGF/SF. This is the first report identifying the presence of significant amounts of HGF/SF in the pleura of patients where malignant spread has occurred.
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