Protein products Terms Links

Fig. 1. Batch growth and antibody production of Nicotiana tabacum (BY-1) cells in terms of pg 1 1 protein, wet cell concentrations, and dry cell concentrations. Dashed vertical lines represent the boundaries between lag, exponential, and stationary growth phases. The 4-day offset between peak concentrations for biomass and protein product indicates that growth and product formation are not directly linked...

In general, the NOS isoforms can be grouped into two classes as determined by their expression in cells. Certain NOS isoforms, termed constitutive, appear to be expressed at a fairly constant level in their host cells. However, these isoforms are inactive in their native state and require that the Ca -binding protein calmodulin associate with them in order to generate NO (Schmidt et al., 1991 Busse and Mulsch, 1990 Bredt and Snyder, 1994). Thus NO production by constitutive NOS isoforms is often linked to Ca +-mediated signal transduction cascades that involve soluble guanylate cyclase, which is a hemeprotein that is activated by NO (Arnold et al., 1977). 

Three amino acids can be joined by two peptide bonds to form a tripeptide similarly, amino acids can be linked to form tetrapeptides, pentapeptides, and so forth. When a few amino acids are joined in this fashion, the structure is called an oligopeptide. When many amino acids are joined, the product is called a polypeptide. Proteins may have thousands of amino acid residues. Although the terms protein and polypeptide are sometimes used interchangeably, molecules referred to as polypeptides generally have molecular weights below 10,000, and those called proteins have higher molecular weights. 

Binding leads to one of two consequences. If the receptor is coupled to an ion channel, the channel is opened, ions move down electrochemical gradients, and the membrane potential is changed. If the receptor is linked to a G protein, the binding initiates a sequence of biochemical events that result in the production of a second messenger such as cAMP or IP3. These evoke long-term changes that alter excitability of the postsynaptic cell. The complexation process is usually rapidly reversible with an occupancy half-life of 1-20 ms. 

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