labeled compound A compound consisting of
radioactively labeled molecules that can be observed as
it passes through physical, chemical, or biological pro-
cesses.
labile The term has loosely been used to describe
either a relatively unstable and transient chemical
species or a relatively STABLEbut reactive species.
See alsoINERT.
laccase A copper-containing ENZYME, 1,4-benzene-
diol oxidase, found in higher plants and microorgan-
isms. Laccases are MULTICOPPER OXIDASEs of wide
specificity that carry out one-electron oxidation of phe-
nolic and related compounds and reduce O 2 to water.
The enzymes are polymeric and generally contain one
each of TYPE1, TYPE2, TYPE 3 COPPERcenters per SUB-
UNIT, where the type 2 and type 3 are close together,
forming a trinuclear copper CLUSTER.
See alsoNUCLEARITY.
lactate Alternate name for lactic acid, a chemical cre-
ated from sugars when broken down for energy in the
absence of oxygen. Strictly, it refers to the deproto-
nated form of lactic acid as it exists as the anion or in
salts and esters, for example.
lactoferrin An iron-binding protein from milk, struc-
turally similar to the TRANSFERRINs.
Landsteiner, Karl(1868–1943) AustrianBiochemist
Karl Landsteiner was born in Vienna on June 14, 1868,
to Leopold Landsteiner, a journalist and newspaper
publisher, and Fanny Hess. Landsteiner studied
medicine at the University of Vienna, graduating in
1891.
From 1898 until 1908 he held the post of assistant
in the university department of pathological anatomy
in Vienna. In 1908 he received the appointment as pro-
sector in the Wilhelminaspital in Vienna, and in 1911
he became professor of pathological anatomy at the
University of Vienna.
With a number of collaborators, he published
many papers on his findings in anatomy and immunol-
ogy, such as the immunology of syphilis and the
Wassermann reaction, and he discovered the immuno-
logical factors, which he named HAPTENs. He also laid
the foundations of the cause and immunology of
poliomyelitis.
His discovery of the major blood groups and
development of the ABO system of blood typing in
1901 and, in 1909, the classification of the bloods of
human beings into the now well-known A, B, AB, and
O groups (as well as the M and N groups), which
made blood transfusion a routine medical practice,
resulted in his receiving the Nobel Prize for physiol-
ogy or medicine in 1930. In 1936 he wrote The Speci-
ficity of Serological Reactions, a classic text that
helped to establish the science of immunochemistry. In
1940 he discovered the Rh factor, the protein on the
surface of red blood cells that determines if the blood159