The Expression of Mouse Tyrosinase in Chick Cells In Vitro and In Vivo When Controlled by a Constitutive Promoter

Virally introduced mouse tyrosinase expression was checked both in vitro and in vivo in chicken cells and tissues. The results indicate that a constitutive promoter is able to express mouse tyrosinase in a variety of cells and tissues both in vitro and in vivo. Tyrosinase expression is marked by pigment production in situ, which is visible at macroscopic as well as microscopic levels without the use of substrates. It is concluded that tyrosinase can be a valuable marker for tracking gene insertion since it is spontaneously expressed. The expression of tyrosinase in some cells and tissues has a detrimental effect, however, and should be controlled by tissue-specific promoters.     

A colorimetric enzyme assay using Escherichia coli to determine nutritionally available lysine in biological materials

A novel bacterial method is described for determining nutritionally available lysine in protein foods with a lysine auxotroph of Escherichia coli (strain M2626). Lysine-dependent synthesis of the induced enzyme bT-galactosidase is determined by a colorimetric method. With this approach sensitivity is increased ca 100-fold and assay time decreased to ca 2 h. The improved procedure was applied to the assay of lysine present as the free amino acid or in small peptides, and after enzymic pre-digestion in vitro with a mixture of pronase and intestinal peptidases, to pure proteins and a variety of feed meals and rice cultivars. In addition, heat treatment of complex samples was shown to lower their content of available lysine, as judged by the decreased nutritional response of the E.coli strain.