124 THE BIOSYNTHESIS OF PROTEINS 



ready made hydroxyproline is not used for the synthesis of these proteins 

 (Steward and Pollack, 1958; Green and Lowther, 1959) or it is a very 

 inefficient precursor if it is used at all (Mitoma et ah, 1959). Hydroxy- 

 proHne exists only in bound form, it arises by a modification of proline 

 after this has been incorporated into polypeptides (Stetten, 1949; Jackson 

 and Smith, 1957; Wolf and Berger, 1958). A special oxidase is involved in 

 the transformation (Van Robertson et ah, 1959). 



Unusual observations have been reported on amylase formation in 

 pancreas extracts. The active enzyme is released from an inactive precursor, 

 it is not made de novo from amino acids in the homogenate. The appearance 

 of amylase activity requires the presence of ATP, threonine and arginine, 

 although these amino acids are not incorporated into the active enzyme 

 (Straub et al., 1953; Straub and Ullmann, 1957; Straub, 1958; Grabowski 

 and Munro, 1960). An activation process of a new type might be operating 

 here. 



Processes of maturation of protein systems may also be mentioned at 

 this point. Reserve proteins of pea seeds undergo a slow evolution after 

 they have been made: the electrophoretic pattern changes, indicating 

 association of many protein components into a few larger units (Danielsson, 

 1952; Snellman and Danielsson, 1953; Raacke, 1957). These changes recall 

 the transformations of gluten which involve oxidation of — SH groups 

 (De Deken et ah, 1953). But here we may have crossed the limit of processes 

 which are not relevant to protein biosynthesis. 



The attachment of a prosthetic group may be spontaneous. This is the 

 case of certain flavoproteins, as shown a long time ago by Theorell (1935). 

 The porphyrin nucleus of catalase can probably find its proper place in the 

 protein moiety since the apo-catalase made by a porphyrin-less mutant of 

 E. coli can combine in vitro with haemin, resulting in a complex endowed 

 with catalase activity (Beljanski, 1955). Certain Staphylococci also make 

 apo-catalase when deprived of haemin, and complete the synthesis of the 

 enzyme if haemin is added ; this later step apparently involves the partici- 

 pation of coenzyme A (Jensen, 1957). Incidentally, these results indicate 

 that the proper folding of the polypeptide chain did not depend on the 

 prosthetic group since apo-catalase was made in its absence. 



These processes give the finishing touch which confers to the individual 

 proteins their typical features and physiological properties, but the bio- 

 chemical problems raised are minor as compared to the making of the 

 chains with their genetically controlled sequence of amino acids. 



(e) Integration of Proteins into Structures 



Association of proteins into structures of a higher level can also occur 

 spontaneously. The best example of this phenomenon is the association of 

 the protein of tobacco mosiac virus into rods resembling the virus, or better 



