Sulfur-containing amino acid, absence

In heavily sulfited white wines containing over 0.5 ppm copper and stored in sealed containers, a reddish-brown deposit may form. This occurs in the absence of oxygen and ferric ions but redissolves readily upon exposure to oxygen. Its formation may be accelerated by exposure to sunlight or heat, and it is believed to consist of colloidal cupric sulfide (14, 29). More commonly, copper casse may arise from reactions between copper and sulfur-containing amino acids, peptides, and proteins (15,16,17). 

Meager information is known about the biogenesis of the cyclopeptide alkaloids. In any event, the specificity of the enzyme system responsible for their formation cannot be very rigid because of the many different bases that are copresent in any plant. Characteristic is the incorporation of a variety of acids with a lipophyllic side chain and the absence of acid, basic, or sulfur containing amino acids. 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

By contrast with vasopressin and oxytocin, these highly purified factors (CRF, GRF, and LRF) had an absence of sulfur-containing amino acids in their molecules. We have already alluded to the resistance of CRF and LRF reduction by thioglycollate which splits the disulfide bridge in the molecules of vasopressin and oxytocin. Consequently, it would appear that the hypothalamic factors which affect pituitary secretion constitute a new family of relatively small, basic polypeptides. 

Induced cells contain a mechanism for concentrating inducers within the cells, and this mechanism appears to play a part in the induction process. The formation of enzyme depends on the continued presence of inducer. The rate of enzyme synthesis with adequate amoimts of inducer is proportional to the growth of the bacteria. When the inducer is removed (by suspending the centrifuged bacteria in fresh medium), enzyme synthesis stops abruptly. The enzyme already formed, however, is stable, and persists unchanged for many generations. Sulfur-labeled amino acids have been used to demonstrate that the induced enzyme is formed directly from free amino acids, and that proteins already in the bacteria do not contribute amino acids to the new enzyme. In the absence of the inducer, the adaptive enzyme retains its label. Some properties of inducers were found in a study of penicillinase production by BadUus cereusJ With this system it was shown that in a brief exposure a small amount of penicillin is specifically bound within the cells, and is not hydrolyzed, but stimulates the production of several equivalents of penicillinase. 

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