at Related Biological Terms

(see charge relay system)

(see turnover number (catalytic-centre activity))

One of a family of phenolic compounds chemically related to catechol (1,2-dihydroxybenzene), which is derived metabolically from tyrosine; the family comprises hormones and neurotransmitters, including adrenaline (epinephrine), noradrenaline, dopamine, etc.

(= concatenate (catenane))

Cathepsin is a cysteine proteinase that degrades elastin and fibrillar collagen. In addition, cathepsin is an endopeptidase associated with lysosomes in the cell, often with low pH optimum. Cathepsins are involved in intralysosomal protein degradation and in a wide range of other physiological and pathological processes. Because of their broad specificity, the cathepsins can obviously compensate for one another. Cathepsins fulfill a unique role among lysosomal proteases. Cathepsins are classified based on their structure and catalytic type into serine (cathepsins A and G), aspartic (cathepsins D and E, present in endosomes), and the most prominent cathepsin family of cysteine cathepsins (cathepsins B, C, F, H, K, L, O, S, V, W, and X), with cathepsins B, C, D, and L being ubiquitously expressed, while the rest exhibit a tissue- or cell-type-specific expression. Cathepsins are also synthesized as inactive pre-proenzymes and undergo posttranslational glycosylation. The activity of cathepsins is regulated at different levels. First, the transcription of cathepsin genes is controlled by cell-type-specific mechanisms and exogenous factors. Thus, different cell types do express different cathepsins.

(see anion)

(see anion)

(see ion-exchange chromatography)

A method for separation of isolated cells according to their characteristic sedimentation rates in a centrifuge rotor which is designed to allow flow-through of a fluid during operation; also known as countercurrent elutriation and elutriation centrifugation. The centrifugal force on the cells is opposed by the force of a fluid moving in the opposite direction. Cells are first sedimented in a density gradient, then displaced by a buffer of increasing density that flows into the bottom of the sample cell and out of the top, and carries with it cells of the same density. Diamond, R.A. (1991) Methods Companion Methods Enzymol. 2, 173-182

A conceptualization of the mechanism of the water-splitting enzyme of photosynthesis in which four electrons are sequentially removed from the manganese centre, enabling it to oxidize water to molecular oxygen.