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protein S 599 protoplast
protein S
A 69-kDa vitamin K-dependent plasma protein that serves as
a cofactor for activated protein C. It occurs as an active single
chain protein or as a dimeric protein that is disulfide-linked
and inactive. Protein S, in the presence of phospholipid,
facilitates protein C inactivation of factor Va and combines
with C4b-binding proteins. Protein S deficiency (autosomaldominant
transmission) is characterized clinically by deep
vein thrombosis, pulmonary thrombosis, and thrombophlebitis.
Laurell rocket electrophoresis is used to assay protein S.
protein SAA
A soluble precursor of AA present in minor quantities in
serum. SAA has a molecular weight of 100 kDa and is present
in cord blood and during the first three decades of life at
an average concentration of 50 ± 40 ng/mL. During the next
three decades, SAA shows a slow but steady increase in
concentration, with the level doubling in the eighth decade
of life. Levels of the serum precursor are elevated in most
patients with amyloidosis except in cases of extreme
protein dysfunction due to severe nephrosis. Levels reaching
700 ng/mL are detectable in patients with tuberculosis,
lymphoma, carcinoma, and leukemia, but SAA levels have
no value in the diagnosis of amyloidosis. High levels of
SAA are seen in the secondary form of the disease. SAA
levels may increase transiently during various infections.
protein separation techniques
Proteins may be purified using both electrophoresis and chromatography.
Individual techniques are discussed individually.
Refer to affinity chromatography, isoelectric focusing,
and SDS–polyacrylamide gel electrophoresis (SDS-PAGE).
protein tyrosine kinases
Enzymes that phosphorylate protein tyrosine residues and participate
in signal transduction from several types of cell surface
receptors such as B cell and T cell receptors for antigen.
proteinuria
Protein in the urine.
proteolipid protein (PLP) autoantibodies
Proteolipid protein is a principal structural protein of the
myelin sheath of the mammalian central nervous system
and plays a critical role in myelination. It has been used to
induce experimental allergic encephalomyelitis (EAE) in
rabbits, producing lesions that resemble those formed in
other species following immunization with whole central
nervous system (CNS) tissue or myelin basic protein (MBP).
The PLP antibody response in rabbits correlates with the
clinical and histopathologic severity of experimental and
allergic encephalomyelitis. PLP autoantibodies are correlated
with a specific subset of multiple sclerosis patients.
proteomics
The study of the total proteins encoded by the genome of an
organism. The study of proteins that an organism manifests
is called expression proteomics.
Proteus immunity
Proteus mirabilis administered to mice by the transurethral
route can induce antibodies that react with purified
lipopolysaccharide, flagella, outer membrane protein
(OMP), and mannose-resistant Proteus-like MR/P fimbriae.
Murine vaccination leads to partial immunity. The sera of
patients with rheumatoid arthritis also react with P. mirabilis.
A hexamer peptide within hemolysin is the target of the
immunogenic response, probably due to its close similarity
to susceptibility sequences of HLA-DR1 and DR4. Several
proteins encoded by chromosomal genes serve as P. mirabilis
virulence factors. These help a host evade immune
defenses and lead to cell and tissue injury and include
urease and HPM hemolysin. The latter leads to lysis of
erythrocytes or epithelial cell membrane injury in culture.
The organism also produces four types of fimbriae, surface
proteins that have a role in adherence. It also secretes a
protease that degrades IgA.
prothrombin antibodies
Antibodies against prothrombin or to the prothrombin–
phospholipid complex have been associated with antiphospholipid
(APF) syndrome. The test is based on the ability of
patient sera to inhibit prothrombin activation to thrombin.
Factor Xa or purified snake venom can cleave prothrombin
to produce thrombin. Prothrombin antibodies in patient sera
inhibit the capacity of these proteins to activate prothrombin.
Prothrombin antibodies prevent prothrombin activation
but do not interfere with prothrombin activity on fibrin and
are therefore associated with thrombosis, not bleeding.
Increased concentrations of antibodies against prothrombin
increase the risk of deep venous thrombosis and pulmonary
embolism in middle-aged men.
prothymocytes
Hematopoietic stem cells from the bone marrow migrate to
the thymus via blood circulation and enter through the epithelial
cell lining of the cortex. Prothymocytes (pre-T cells)
differentiate in the thymus microenvironment. They are educated
in the thymus to function as T cells. The four thymic
peptide hormones are thymulin, thymosin α, thymosin β, and
thymopoietin. These hormones are significant in T lymphocyte
proliferation and differentiation. Direct interaction with
the thymus epithelium, which expresses human leukocyte
antigens (HLAs), is necessary for forming functional T lymphocytes
and for learning to recognize major histocompatibility
complex (MHC) antigens. Prothymocytes proliferate
and migrate from the cortex to the medulla. Some are shortlived
and die. The long-lived cells acquire new characteristics
and are called thymocytes. They exit the thymus as immature
cells and seed specific areas of the peripheral lymphoid
organs where they continue to differentiate through a process
driven by an antigen. From these areas, they recirculate
throughout the body.
protooncogene
A cellular gene that shows homology with a retroviral oncogene.
It is found in normal mammalian DNA and governs
normal proliferation and probably also differentiation of
cells. Mutation or recombination with a viral genome may
convert a protooncogene into an oncogene, signifying that it
has become activated. Oncogenes may act in the induction
and/or maintenance of a neoplasm. Protooncogenes united
with control elements may induce transformation of normal
fibroblasts into tumor cells. Examples of protooncogenes
are c-fos, c-myc, c-myb, c-ras, etc. Alteration of the protooncogenes,
leading to synthesis of an aberrant gene product,
is believed to facilitate their tumorigenesis. An elevation in
the quantity of gene product produced is also believed to be
associated with tumorigenesis of protooncogenes.
protoplast
A bacterial cell from which the wall has been removed. It
includes the cell protoplasm and the cytoplasmic membrane.
Lysozyme digestion of Gram-positive bacteria that contain
peptidoglycan cell walls yields protoplasts that require
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