Primary Proteolysis

Those studies in which the effect of fat on primary proteolysis has been studied indicate that the effect depends on the level of MNFS in the cheese. 

Banks et al. (1989) found that a 50% reduction in the fat content of Cheddar cheese only slightly reduced the level of water-soluble N at 2 (9.9 vs. 11.8 g/lOOg N) or 4 (15.3 vs. 17.8 g/lOOg N) months. Likewise, 

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Grappin, R., Rank, T. C. and Olson, N. F. 1985. Primary proteolysis of cheese proteins during ripening. A review. J. Dairy Sci. 68, 531-540. 

Several of the smaller volatile compounds formed from the catabolism of products of primary proteolysis (e.g., amino acids) can be determined by GC. The development of capillary columns and interfacing GC with MS has noticeably increased the sensitivity of this analysis. Over 200 volatile compounds have been identified in Cheddar cheese. A list of several of these compounds can be found elsewhere (Fox et ah, 2004a Singh et ah, 2003). The instrumental techniques available for the characterization of cheese aroma were also discussed recently (Le Quere, 2004 Singh et al., 2003). 

As would be expected of active protein secreting cells, glandular epithelial tissue, the cytokine secreting cells of the immune system and the blood vessel endothelium, have an extensive internal structure consisting of rough endoplasmic reticulum and numerous mitochondria. Peptide hormones, growth factors and cytokines like all proteins are synthesized by DNA transcription and mRNA translation. The primary transcript of the mRNA may code for an inactive prohormone which requires careful proteolysis to produce the active hormone, as for example in the case of insulin. Adrenocorticotropic hormone (ACTH) is particularly interesting in this respect because... 

In conjunction with studies performed by van Leeuwen et al. (135-138), Layfield et al. (263) proposed a novel mechanism that could account for an inhibition of 26S proteasome activity in cases of nonfamilial AD. Mutant forms of ubiquitin may inhibit proteolysis within neurons, predisposing these cells to inclusion formation. Molecular misreading of the UBB gene results in a dinucleotide deletion in UBB mRNA (135-138,264). In AD, an age-related posttranscriptional defect in primary transcript RNA processing may occur, leading to dinucleotide deletions within open reading frames that result in frameshifts and produce abnormal extension proteins, as demonstrated by van Leeuwen and coworkers (138). 

The Daily Industiy. The first step in cheese manufacture is the coagulation of milk. Coagulation can be divided into two distinct phases, enzymatic and the non-enzymatic. In the primary enzymatic phase a proteol ic enzyme such as chymosin (rennet), or less effectively, pepsin, carries out an extremely specific and limited proteolysis, cleaving a phenylalanine-methionine bond of /c-casein, making the casein micelle metastabie. In the second, non-enzymatic phase, the... 

Fig. 1.46. Alternative polyadenylation in the expression of calcitonin genes of rat. The primary transcript of the calcitonin gene possesses two polyadenylation sites. One site is nsed in the processing of RNA in the thyroid, another site in the brain, and yet another in nerve tissne. The translation of the two mRNAs creates two pre-hormones, from which two different polypeptide hormones (calcitonin and the calcitonin-related peptide", or CGRP) are created via proteolysis.

Many proteins and glycoproteins are first synthesized in the form of a protein that is larger than the final product. Here, the primary translation-product is subject to one or more steps of controlled proteolysis.430 Good model-systems for study of the conversion of a precursor protein into the final product are cells infected with enveloped viruses,229,431-435 such as influenza, Semliki Forest, Sindbis, and avian sarcoma viruses (and others). Some of these viruses stop synthesis of... 

During ripening, three primary biochemical events occur, glycolysis, lipolysis and proteolysis. The products of these primary reactions undergo numerous modifications and interactions. The primary reactions are fairly well characterized but the secondary changes in most varieties are more or less unknown. An overview of the principal biochemical changes follows. 

FIGURE 12-50 Initial events of apoptosis. Receptors in the plasma membrane (Fas, TNF-R1) receive signals from outside the cell (the Fas ligand or tumor necrosis factor (TNF), respectively). Activated receptors foster interaction between the "death domain" (an 80 amino acid sequence) in Fas or TNF-R1 and a similar death domain in the cytosolic proteins FADD or TRADD. FADD activates a cytosolic protease, caspase 8, that proteolytically activates other cellular proteases. TRADD also activates proteases. The resulting proteolysis is a primary factor in cell death. 

Peptides extracted from casein with N, N-dimethyl formamide have complex electrophoretic patterns identical to those of the fraction first prepared by Long and co-workers and called X-casein (El-Negoumy 1973). These peptides are identical electrophoretically to those released by the action of plasmin, which is present in fresh raw milk, upon asr casein (Aimutis and Eigel 1982). Two of these peptides have tryptic peptide maps and molecular weights identical to those of a pair of the peptides produced by plasmin degradation of asl-casein. These peptides appear to be fragments of a8l-casein which are present in milk as the result of plasmin proteolysis. More definitive information on their primary structure is needed before nomenclature for these fragments can be established. 

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