Growth protein requirements

Different feeding standards adopt different approaches to estimate energy and protein requirements for growth. Protein requirements for pigs and poultry are generally more detailed than those of ruminants and horses because they include estimates of requirements for specific amino acids. 

Nutritional Requirements. The nutrient requirements of mammalian cells are many, varied, and complex. In addition to typical metaboHc requirements such as sugars, amino acids (qv), vitamins (qv), and minerals, cells also need growth factors and other proteins. Some of the proteins are not consumed, but play a catalytic role in the cell growth process. Historically, fetal calf semm of 1—20 vol % of the medium has been used as a rich source of all these complex protein requirements. However, the composition of semm varies from lot to lot, introducing significant variabiUty in manufacture of products from the mammalian cells. 

FIGURE 16.28 HIV mRNA provides the genetic information for synthesis of a polyprotein. Proteolytic cleavage of this polyprotein by HIV protease produces the individnal proteins required for viral growth and cellular infection. 

The nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are the chemical carriers of a cell s genetic information. Coded in a cell s DNA is the information that determines the nature of the cell, controls the cell s growth and division, and directs biosynthesis of the enzymes and other proteins required for cellular functions. 

In addition to protein impurities emanating directly from the source material, other proteins may be introduced during upstream or downstream processing. For example, animal cell culture media are typically supplemented with bovine serum/foetal calf serum (2-25 per cent), or with a defined cocktail of various regulatory proteins required to maintain and stimulate growth of these cells. Downstream processing of intracellular microbial proteins often requires the addition of... 

The most commonly used culture system for scale-up of E. coli is the shake flask. This conventional methodology has been shown to produce the quantity and quality of protein required with good scalability from plate-based expression screening. In general, cell-line, medium, growth conditions, and induction method are determined by the small-scale expression screen. Typically, the shake-flask is filled to one-quarter of its capacity to allow for adequate aeration of the culture. The generic OPPF... 

Wellner, M., Maasch, C., Kupprion, C., Lindschau, C., Luft, F. C., et al. 1999. The proliferative effect of vascular endothelial growth factor requires protein kinase C-alpha and protein kinase C-zeta. Arterioscler. Thromb. Vase. Biol. 19 178-185. 

Some cell lines, such as Namalwa, can grow satisfactorily in medium in which the only protein is albumin. Other cell lines show distinct protein requirements, such as albumin, transferrin, and insulin, or the addition of polypeptide growth factors, isolated from non-serum sources that have shown stimulation of many cell types in culture. Some cells have very fastidious growth requirements and their stability and productivity may be reduced significantly in serum-free media. 

The remainder of this chapter takes on a more "nutritional" aura, ft concerns the concepts of growth and maintenance- The material may be especially intcresling to those involved in infant nutrition, animal science, and weight reduction by low-energy diets. The material reveals the tecliniques used for determining the protein requirement and the recommended daily allow ancc (RDA) for protein. Clinical issues involving protein nutrition, such as renal disease and gput, arc also Outlined. 

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