Structure, properties, and engineering of the major zinc binding site on human albumin

Influência do trauma cirúrgico no comportamento dos níveis séricos de albumina após cirurgia da coluna vertebral

OBJETIVO: avaliar a variação da concentração da albumina nas cirurgias de coluna vertebral e relacioná-la às repercussões clínicas no pós-operatório. MÉTODOS: estudo prospectivo observacional sobre os valores do nível sérico da albumina de 55 pacientes submetidos à cirurgia na coluna vertebral. As amostras de sangue foram coletadas um dia antes da cirurgia e 24 horas após o procedimento. Foi aplicado o teste t pareado na avaliação da variação (pré versus pós) nos parâmetros albumina, hemoglobina e hematócrito. A presença de associação entre grau de variação nos níveis de albumina (<1 g/dL ou >1 g/dL) e as variáveis de interesse: presença de complicações, necessidade de transfusão, procedimento realizado, idade e gênero do paciente e diagnóstico foram avaliadas pelo teste do χ2 de Pearson ou teste do χ2 da razão de verossimilhança quando apropriado. RESULTADOS: a redução média dessa proteína foi de 0,58 g/dL, variando de 0 a 1,8 g/dL. Dos pacientes, 78,2% apresentaram valores da albumina no período pós-operatório abaixo da faixa considerada normal. Somente dois pacientes da amostra apresentaram complicações durante os 30 dias de seguimento. O grupo com correção de deformidades apresentou 100% de pacientes com variação >1 g/dL. CONCLUSÃO: houve influência do trauma cirúrgico na redução sérica da albumina, em média, de 0,58 g/dL nas cirurgias da coluna vertebral. Não foi possível associar essa queda às complicações no período pós-operatório após seguimento de 30 dias desses pacientes.

Metal ions and electrolytes regulate the dissociation of heme from human hemopexin at physiological pH

The stability of the hemopexin-heme (Hx-heme) complex to dissociation of the heme prosthetic group has been examined in bicarbonate buffers in the presence and absence of various divalent metal ions. In NH(4)HCO(3) buffer (pH 7.4, 20 mm, 25 degrees C) containing Zn(2+) (100 microm), 14% of the heme dissociates from this complex (4.5 microm) within 10 min, and 50% dissociates within 2 h. In the absence of metal ions, the rate of dissociation of this complex is far lower, is decreased further in KHCO(3) solution, and is minimal in NaHCO(3). In NH(4)HCO(3) buffer, dissociation of the Hx-heme complex is accelerated by addition of divalent metals with decreasing efficiency in the order Zn(2+) > Cu(2+) >> Ni(2+) > Co(2+)>>Mn(2+). Addition of Ca(2+) prior to addition of Zn(2+) stabilizes the Hx-heme complex to dissociation of the heme group, and addition of Ca(2+) after Zn(2+)-induced dissociation of the Hx-heme complex results in re-formation of the Hx-heme complex. These effects are greatly accelerated at 37 degrees C and diminished in other buffers. Overall, the solution conditions that promote formation of the Hx-heme complex are similar to those found in blood plasma, and conditions that promote release of heme are similar to those that the Hx-heme complex should encounter in endosomes following endocytosis of the complex formed with its hepatic receptor.

Albumin and mammalian cell culture: implications for biotechnology applications

Albumin has a long historical involvement in design of media for the successful culture of mammalian cells, in both the research and commercial fields. The potential application of albumins, bovine or human serum albumin, for cell culture is a by-product of the physico-chemical, biochemical and cell-specific properties of the molecule. In this review an analysis of these features of albumin leads to a consideration of the extracellular and intracellular actions of the molecule, and importantly the role of its interactions with numerous ligands or bioactive factors that influence the growth of cells in culture: these include hormones, growth factors, lipids, amino acids, metal ions, reactive oxygen and nitrogen species to name a few. The interaction of albumin with the cell in relation to these co-factors has a potential impact on metabolic and biosynthetic activity, cell proliferation and survival. Application of this knowledge to improve the performance in manufacturing biotechnology and in the emerging uses of cell culture for tissue engineering and stem cell derived therapies is an important prospect.

Plasma fatty acid levels may regulate the Zn(2+)-dependent activities of histidine-rich glycoprotein

Histidine-rich glycoprotein (HRG) is a plasma adaptor protein involved in the formation of protein complexes that regulate a number of biological processes in the blood, most notably coagulation and the immune system. Elevated levels of HRG are clinically linked to thrombotic disorders such as blood vessel occlusion. A large body of evidence suggests that Zn(2+) ions stimulate HRG-complex formation; however, under normal conditions the vast majority of Zn(2+) in the blood is bound to human serum albumin (HSA). We have previously demonstrated that high levels of fatty acid act as an allosteric switch which disrupts the major Zn(2+)-binding site on HSA. Transient or sustained elevation of plasma fatty acid levels may therefore increase the proportion of plasma Zn(2+) associated with HRG. We speculate that this mechanism may potentiate an increased risk of thrombosis in individuals with elevated fatty acid levels such as those associated with cancer, obesity and diabetes.