While studying at Berkeley, Ludwig took Howard Schachman's course in physical biochemistry; she later credited this course with setting the direction for her own research. She completed her Ph.D. thesis on the biosynthesis of
ergothionine at
Cornell University Medical College, and followed this with postdoctoral studies at
Harvard Medical School from 1957 to 1959 and the
Massachusetts Institute of Technology from 1959 to 1962. In 1962 Ludwig's interests switched from classical techniques of biochemistry to the then-emerging field of
X-ray crystallography and she joined the laboratory of
William Lipscomb to work on the structure of
carboxypeptidase. Ludwig determined the structure of the enzyme
carboxypeptidase A, one of the first enzyme structures to be described. In 1967, she became an assistant professor in the Department of Biological Chemistry and an assistant research biophysicist in the Biophysics Research Division at the
University of Michigan. As a faculty member in the Biophysics Research Division, she joined a group of other faculty including
Vincent Massey (enzymologist) and Graham Palmer; focusing on studying flavoproteins. Ludwig focused on studying
flavodoxin in her laboratory. In 1969, Ludwig had her first publication which focused on the crystallization of both oxidized and semiquinone forms of protein from Clostridium pasteurianum. Ludwig also worked on
superoxide dismutase during the 1980s with James Fee, a colleague from the Biophysics Research Division at the University of Michigan. In 1990, Ludwig continued to collaborate with
University of Michigan colleagues including Vincent Massey, to uncover why there was a very low potential associated with the reduction of semiquinone. Ludwig started a collaboration with Richard Swenson from Ohio State University, where they examined the redox state of a flavodoxin from
Clostridium beijerinckii. Her laboratory focused on proteins involved in electron and group transfer reactions; over the next four decades it helped elucidate, amongst others, the structures of
flavodoxin, the first
flavoprotein structure, iron-superoxide dismutase,
p-hydroxybenzoate hydroxylase and phthalate dioxygenase reductase. Ludwig continued close collaborations with faculty studying redox biology at the University of Michigan, resulting in structure determinations of phthalate dioxygenase reductase in collaboration with the laboratory of
David Ballou, p-hydroxy-benzoate hydroxylase in collaboration with the laboratories of Ballou and
Vincent Massey,
thioredoxin reductase in collaboration with the laboratory of Charles Williams Jr., and cobalamin-dependent methionine synthase in collaboration with
Rowena Green Matthews. == Service ==