Protein biosynthesis, errors

The activity of a very weak active mutant measured by steady state kinetics could result from traces of a wild-type or more active mutant in the preparation either as a contaminant or because of natural errors of misincorporation. The error rate in protein biosynthesis can be as high as one part in 100 or one part in 1000.10 The presence of a small amount of wild-type enzyme in an inactive mutant would give a low value of kcat (which is directly proportional to the concentration of wild type) but the KM value for the wild-type enzyme. Thus, the finding of a low value of kcat and the wild-type KM for a mutant is very suspicious. 

In all these events, the hydrogen-bonded Watson-Crick base pair is operative and is responsible for DNA reduplication, transcription, and translation. Since mispairing can occur, all these processes are checked for fidelity by several enzymes which can correct for errors [6521. At this and all other levels of DNA reduplication and protein biosynthesis, intermolecular hydrogen bonds between nucleic acids and between nucleic acids and proteins are responsible for recognition, interaction, and, finally, for information transfer. 

PAGE, but often relatively easy to do so by IEF. Protein phosphorylation is another example where IEF is the technique of choice it can be used readily to separate phosphorylated and non-phosphorylated forms of the protein on the strength of charge differences, whereas SDS-PAGE would scarcely be able to separate them on the basis of such a small difference in mass. The charge resolution of IEF is so great that it is possible to use the technique to reveal the occurrence of errors in protein biosynthesis when these errors result in incorporation of a charged amino acid in place of a neutral one, or vice versa, the variant proteins produced form satellite bands around the major protein band. 

Freist, W. Sternbach, H. Pardowitz. I. Cramer. F. Accuracy of protein biosynthesis Quasi-species nature of proteins and possibility of error catastrophes. J. Theor. Biol. 1998. 193. 19-38. 

Sucrase (also called saccharase and invertase) hydrolyzes sucrose. In contrast to the abundant information available on the yeast invertase, little is known of the mammalian sucrases. The significance of invertase and lactase in absorption is illustrated by inborn errors of metabolism in which these two enzymes are absent in the intestinal secretion. (The fact that lactase deficiency does not interfere with growth indicates that the galactose needed for biosynthesis of brain lipids or lens proteins can be synthesized endogenously in amounts sufficient to fulfill the metabolic requirements.) In that case, there is an intolerance to lactose or sucrose with no increase in blood glucose levels or without an increase in the levels of disaccharides... 

Homocystinuria and hyperhomocyst(e)inemia are biochemical denominators for deficiencies of CBS, MTHFR, cbIC-G, and transcobalamin II, the major protein carrier of cobalamin in plasma [1, 3, 6]. Patients with the latter disorder or with inborn errors of cobalamin biosynthesis resulting in combined deficiency of both adenosylcobalamin and methylcobalamin also have... 

A basic amino acid found in many proteins. It is also involved in urea biosynthesis. In the inborn error, cystinuria, it is excreted in the urine in large amounts, along with other basic amino acids. 

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