Final answer:
Histidine and glutamate are examples of conditionally indispensable amino acids, which are non-essential under normal circumstances but can become essential in specific conditions like PKU.
Step-by-step explanation:
The amino acids histidine and glutamate are examples of conditionally indispensable amino acids. This means that they are typically non-essential, as they can be synthesized by the human body under normal conditions. However, in certain circumstances, such as with specific diseases or metabolic disorders, these amino acids become essential and must be obtained from the diet. One example is the condition phenylketonuria (PKU), where individuals with PKU lack the enzyme needed to convert the amino acid phenylalanine into tyrosine, making phenylalanine and tyrosine conditionally indispensable amino acids for these individuals.
Glutamate is often synthesized from alpha-ketoglutarate and ammonia, a process involving glutamate dehydrogenase. As such, it is typically classified as non-essential. However, in certain physiological states such as trauma, illness, or inborn metabolic disorders, the synthesis of glutamate may not meet the body's demands, rendering it conditionally indispensable.
It's important for those with metabolic disorders or specific health conditions to adhere to dietary guidelines that ensure sufficient intake of conditionally indispensable amino acids to prevent deficiencies and maintain overall health.