Mayfield…First of all, I would not recommend whey protein as a standalone source of protein at any other time during the day outside of: before, during and/or after training. The rest of the time, this will not serve as an optimal source of amino acids (read JB’s Bedtime Story for more details). If you do choose whey during the day, then add a whole-food source of protein to it. This might even be more optimal than consuming whole-food protein alone.
Now, I’ll give you a smart-ass answer to your question about “How much protein can one use in one sitting…” All of it!
All dietary protein is broken down into its consituent amino acids during digestion and absorption. Because there is no storage pool for amino acids like glucose or fatty acids (i.e. glycogen, adipose tissue, intramuscular triglycerides), the body must utilize the amino acids in one way or another.
The most likely scenario is that the amino acids will be used for protein synthesis and tissue turnover–remember from all of JB’s articles on protein (i.e. Protein Prejudice) that the functions of amino acids are not simply to build muscle–although it is what we want to be the first priority.
In the case that there are excess amino acids, the nitrogen component of the amino will be cleaved off (i.e. deamination), leaving a carbon skeleton. All macronutrients are bonds of carbon, hydrogen and oxygen, with protein having the unique nitrogen component.
Because some amino acids are considered ketogenic and some are considered gluconeogenic, the fate of these deaminated amino acids will vary. Those that are ketogenic will–after deamination–be incorporated into the cycle of fat metabolism. One fate of these is to be stored as triglyceride if not used for energy. The gluconeogenic precursors, on the other hand, will be incorporated into the metabolic cycles specific to glucose.
I hope this little physiology lesson helps, and once again shows why it’s so difficult to store protein as fat and that one should maximize protein intake.
As far as your original question, my answer is: I don’t know! Honestly, just try to meet your desired protein requirements. I would rather see a balance of protein throughout the day; however, you’ll still see advocates of the protein pulse type diets.