Enzyme-specific inducer

Tandem mass spectrometry (MS/MS) produces precise structural or sequence information by selective and specific induced fragmentation on samples up to several thousand Daltons. For samples of greater molecular mass than this, an enzyme digest will usually produce several peptides of molecular mass suitable for sequencing by mass spectrometry. The smaller sequences can be used to deduce the sequence of the whole protein. 

Urokinase (from human urine) [9039-53-6] Mr 53,000, [EC 3.4.21.31]. Crystn of this enzyme is induced at pH 5.0 to 5.3 (4") by careful addition of NaCl with gentle stirring until the soln becomes turbid (silky sheen). The NaCl concentration is increased gradually (over several days) until 98% of saturation is achieved whereby the urokinase crystallises as colourless thin brittle plates. It can be similarly recrystd to maximum specific activity [104K CTA units/mg of protein (Sherry et al. J Lab Clin Med 64 145 1964)]. [Lesuk et al. Science 147 880 1965 NMR Bogusky et al. Biochemistry 28 6728 1989.] It is a plasminogen activator [Gold et al. Biochem J 262 1989 ]. 

The INDUCED-FIT model for enzyme specificity says that good substrates must be able to cause the enzyme to change shape (conformation) so that catalytic and functional groups on the enzyme are brought into just the right place to catalyze the reaction. Bad substrates are bad because they aren t able to make the specific interactions that cause the conformation change, and the enzyme stays in its inactive conformation. 

Maxwell, C.A. et al., Molecular characterization and expression of isoliquiritigenin 2 -0-methyltransferase, an enzyme specifically involved in the biosynthesis of an inducer of Rhizobium meliloti nodulation genes. Plant J., 4, 971, 1993. 

These are substrates and products which are metabolized in vivo. A natural substrate is only given if it is mentioned in the literature. The commentary gives information on the pathways for which this enzyme is important. If the enzyme is induced by a specific compound or growth conditions, this will be included in the commentary. In Additional information you will find comments on the metabolic role, sometimes only assumptions can be found in the references or the natural substrates are unknown. 

Induced fit. Chapter 12 also pointed out that kcat/KM for enzymes involving induced fit is just the value of kcJKM for the active conformation scaled down by a constant factor for all substrates (equations 12.15 and 12.18). Induced fit does not alter the relative values of kcat/KM from what they would be if all of the enzyme were in the active conformation, and thus does not affect specificity. 

Fig. 4.3 Models of enzyme specificity lock and key (top) and induced fit (bottom)...

The elegance of enzyme reactivity is unparalleled in synthetic catalytic materials. Beginning from ilic time slicn liinil l isclicr proposed his classic lock-and-kcy theory for enzyme specificity to the induced fit theory of Koshland, enzyme catalysis sets the standard to which all other catalytic transformations are compared. 

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