Freezing, enzyme activity

Figure 14.8. Thermograms for the volatilization of peptide-derived compounds in freeze-dried rhizodeposits leached from a soil cropped with maize after a daytime and a nighttime growth period and thermogram for the volatilization of L-glutamic acid. Reprinted from Leinweber, P., Jandl, G., Baum, C., Eckhardt, K.-U., and Kandeler, E. (2008). Stability and composition of soil organic matter control respiration and soil enzyme activities. Soil Biology and Biochemistry 40,1496-1505, with permission from Elsevier.

Figure 8. Effect of Vacuum drying vs Freeze Drying on enzyme activity.

ER of adrenal, testis, ovary, liver and placenta. It is relatively unstable, being inactivated by freezing, even when pure. A phospholipid environment appears to be an important requirement since, when bovine adrenal microsomal preparations were treated with phospholipase A, 80-85% of phospholipids were hydrolysed with a concomitant loss of 80-90% of enzymic activity [84], Restoration of activity was achieved by adding back to the lipid-depleted membranes aqueous dispersions of microsomal total lipid mixtures [84],... 

Carpenter, J.F., S. Prestrelski, and T. Arakawa (1995). Separation of freezing- and drying-induced denaturation of lyophilized proteins using stress-specific stabilization. 1) Enzyme activity and calorimetric studies. Arch. Biochem. Biophys. 303 456—464. 

Answer After an ear of corn has been removed from the plant, the enzyme-catalyzed conversion of sugar to starch continues. Inactivation of these enzymes slows down the conversion to an imperceptible rate. One of the simplest techniques for inactivating enzymes is heat denatura-tion. Freezing the corn lowers any remaining enzyme activity to an insignificant level. 

Freeze-quenching technique in combination with ESR and Mossbauer spectroscopy was used for monitoring intermediates in the reaction of substrate free 57Fe-P450C8Itl with peroxy acetic acid (Schunemann et al., 2000). In such a condition, the oxidant oxidized the enzyme active site iron (III) to iron (VI) and Tyr 96 into tyrosine radical, 90% and 10% from the starting material, respectively. Thus the tyrosine residue may be involved in the catalytic process. 

The assay has been used with mitochondrial extracts prepared from freeze-thawed mitochondria from rabbit and pigeon, and to monitor enzyme activity during purification. 

Retinal oxidase was assayed in a medium containing 0.1 M phosphate buffer (pH 7.7) and 10 piL of 25 mM retinal dispersed in acetone containing 5% Triton X-100. The reaction was initiated by adding 20 to 40 fih of reconstituted ammonium sulfate precipitate or cytosol. The final volume was 500 /xL. The reaction was continued at 37°C for 30 minutes and was stopped by freezing at -70°C, whereupon 50 juL was injected directly onto the column. Enzyme activity was linear with protein concentration up to 2.4 mg/mL, and with time up to 30 minutes. 

It is generally stated that biocatalysis in organic solvents refers to those systems in which the enzymes are suspended (or, sometimes, dissolved) in neat organic solvents in the presence of enough aqueous buffer (less than 5%) to ensure enzymatic activity. However, in the case of hydrolases water is also a substrate and it might be critical to find the water activity (a ) value to which the synthetic reaction (e.g. ester formation) can be optimized. Vahvety et al. [5] found that, in some cases, the activity of Candida rugosa lipase immobihzed on different supports showed the same activity profile versus o but a different absolute rate. With hpase from Burkholderia cepacia (lipase BC), previously known as lipase from Pseudomonas cepacia, and Candida antarctica lipase B (CALB) it was found that the enzyme activity profile versus o and even more the specific activity were dependent on the way the enzyme was freeze dried or immobihzed [6, 7]. A comparison of the transesterification activity of different forms of hpase BC or CALB can be observed in Tables 5.1 and 5.2, respectively. 

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