Protein sub-units

II. Iborra, F., and Buhler, J. M., Protein sub-unit mapping. A sensitive high resolution method. Anal. Biochem. 74, 503-511 (1976). 

High yields of this inhibitor have been recovered by sub-unit exchange chromatography, in which protein sub-units are immobilized on a solid matrix and interact with sub-units in solution. 

Figure 3.6 The tobacco mosaic virus (TMV) consists of identical protein sub-units arranged around an RNA strand. The units invoived are large enough to be imaged by electron microscopy. Reproduced with permission from P. J. G. Butler, Self-assembly of tobacco mosaic virus the roie of an intermediate aggregate in generating both specificity and speed, Phil. Trans. R. Soc., London, B, 354, 537-550 1999 The Royal Society.

Egg-white contains several distinct antigens such as ovalbumin, ovoglobulin, ovomucoid, ovomucin, conalbumin and lysozyme [283, 663] and immunochemical techniques have been used to characterize them [131, 338, 674]. Kaminski and Ouchterlony [341] used a combination of precipitation methods and electrophoresis to show 10 antigenically distinct fractions in egg-white. Tiselius and Eriksson-Quensel [621] had earlier indicated that ovalbumin is not electrophoretically homogeneous and subsequent electrophoretic studies showed that ovalbumin and conalbumin each separated into 2 fractions and ovoglobulin separated into 3 [118, 179, 180, 419, 424]. Other studies show that there may even be more protein sub-units in egg-white [48, 129, 144,184, 358, 359, 516]. 

Surface-active proteins can be extracted from a variety of plant sources, including legumes and cereals [60]. A considerable amount of research has been carried out to establish the ability of these proteins to stabilize emulsions, and whether they could be made into commercially viable value-added ingredients for utilization as emulsifiers in foods [90, 91]. One of the most widely studied proteins extracted from a plant source is soy protein, which is commercially available as a protein concentrate or isolate [92-95]. Soy protein ingredients are a complex mixture of many individual protein fractions with different molecular and functional characteristics (e.g. 2S, 7S, US, and 15S fractions) [60]. In addition, each of these fractions contains a mixture of different protein sub-units that also have different molecular and functional characteristics. 

The structure of [NiFeJ-hydrogenase from the bacterium Desulfovibrio gigas (D. gigas) has been crystallographically determined. It consists of two protein sub-units. The smaller unit contains one [3Fe-4S] and two [4Fe-4S] clusters. Pairs of adjacent clusters are 1200 pm apart and the three clusters form an electron-transfer pathway from the active site (which is located in the larger sub-unit. Fig. 29.19a) to the... 

Figure 4.9 Model of Flagellar Rotation (after Berg, 1975). The lower M-ring consists of 16 protein sub-units, opposed to a similar fixed fing, the S-ring. Passage of a proton, in response to the protonmotive force, through each M-ring sub-unit causes the rotation of the flagellum through one-sixteenth of a turn, i.e. 256 protons would be consumed in each complete revolution.

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