Protein History — Identify the first protein whose complete three-dimensional tertiary structure was determined by X-ray crystallography.

Introduction:Determining the first complete protein structure was a landmark in structural biology, validating methods of X-ray crystallography and revealing how amino acid sequence folds into 3D form.

Given Data / Assumptions:

• X-ray crystallography was the key method used in early structural determinations.
• Historical precedence matters; sequencing and structure are different accomplishments.
• Several candidate proteins were characterized around the same era.

Concept / Approach:Differentiate between 'first sequenced protein' and 'first solved 3D structure'. Insulin was first sequenced, but the first tertiary structure solved at atomic resolution was for myoglobin.

Step-by-Step Solution:

Verification / Alternative check:Historical records in structural biology consistently cite myoglobin as the first complete protein structure, followed closely by hemoglobin.

Why Other Options Are Wrong:

Common Pitfalls:Conflating 'first sequenced' with 'first structurally solved' or assuming enzymatic prominence correlates with historical order.

Final Answer:Myoglobin.