Inactivation by freezing

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],... 

The first protein hypothesis explained freezing injury by a precipitation of proteins due to the freeze-induced increase in salt concentration. This concept is opposed by the absence of a reduction in the activity of most enzymes in freeze-killed plants. Many results point to membranes, and more specifically to their ATPases as the initial locus of freezing injury. Due to their role as ion pumps, their inactivation by freezing is the probable cause of the well-known efflux of ions from freeze-injured tissues. Freezing tolerance of plants is apparently associated with protein changes in both quality and quantity, and also with the accumulation of protective substances that prevent ATPase inactivation. 

In agreement with the membrane concept, Heber (15) investigated a number of enzymes and found that none of the soluble ones were inactivated by freezing. The only one affected by freezing was the... 

Occasionally extracts have been found to be inactivated by freezing and thawing. One possible cause of this may be the failure to remove buffer completely before lysis or it may simply be that the products from some batches of eggs are compromised in... 

STABILIZATION BY PRPP OF CELLULAR PURINE PHOSPHORIBOSYL-TRANSFERASES AGAINST INACTIVATION BY FREEZING AND THA ING. STUDY OF NORMAL AND HYPOXANTHINE-GUANINE PHOSPHORIBOSYL-TRANSFERASE DEFICIENT HUMAN FIBROBLASTS... 

FIG. 1. Sensitivity of fibroblast HGPRT arid APRT to inactivation by freezing and thawing. Dependence on cell concentration. 

TABLE 1. DEPENDENCE OF PHOSPHORIBOSYLTRANSFERASE INACTIVATION BY FREEZING AND THAWING ON CELL CONCENTRATION AND PRESENCE OF PRPP... 

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