28 



two components of different destructive activity. It is perhaps more accurate 

 to state that the enzyme renders thiamine biologically inactive or unavailable, 

 rather than to refer to its destruction. One process of destruction has been 

 demonstrated to be a hydrolytic splitting of the molecule into its two heterocyclic 

 components , generally referred to as the thiazole and pyrimidine fractions . 



It is interesting to note that thiaminase has chiefly been found in what may 

 be broadly called "aquatic animals." All early reports recorded its presence 

 only in fresh-water fish, with the exception of the Atlantic herring. In fish, 

 the greatest concentrations of thiaminase are in the viscera, but it is also widely 

 distributed in the head, skin, and other parts of the fish. There is some contro- 

 versy as to whether thiaminase is present in the flesh when present elsewhere in 

 the body. 



Carp, smelt, and herring are the most important species listed as containing 

 the enzyme, with some 10 or 12 less valuable species; such as, suckers, chubs, 

 burbot, and catfish also containing it. Generally speaking, only a few limited 

 investigations for the determination of the presence of thiaminase have been made 

 of fresh-water species and more especially of the marine species of fish. 



Since 1944, thiaminase has been found in a few other strictly marine "animals"; 

 namely, the hard clam, the ocean or black quahog, and the edible mussel. The men- 

 haden has joined the herring as the only true fish in salt water known to contain 

 it. 



The occurrence of thiaminase in starfish adds an entirely new phylum of aquatic 

 animals to the list of those which contain the enzyme. That it has not been re- 

 ported in other echinodermata , or in unrelated types of marine invertebrates, is 

 readily explained by the fact that no assays have been, or seem likely to be, carried 

 out . This type of investigation would serve no practical purpose but might throw 

 light on the present very confusing distribution of thiaminase in nature and on 

 its function in metabolism. 



Sautier (1946) included 3 species of starfish from Alaskan waters in his 

 list of fishery products assayed for thiamine by the thiochrome method. These 

 sjiecies, Pisaster giganteus , Pisaster ochraceus , and Phycnopodia helianthoides , 

 were reported to contain thiamine within the range of 6 to 17 micrograms per 100 

 grams (5 assays) . 



The only other reference to the presence of thiamine in starfish, is that of 

 Hutchinson, et al, (1946) who reported 1 milligram per kilogram of starfish meal. 

 They state that, "The low thiamine content of the dried starfish is almost cer- 

 tainly due to post-mortem loss." 



Myers (1946), of this laboratory, has found that the thiochrome assay as 

 generally used is of doubtful applicability to the assay of thiamine in fishery 

 products. It is possible that some starfish may contain thiamine and others thia- 

 minase, as similar apparent contradictions have been reported in regard to some 

 species of fish. There are insufficient data to determine the true status of 

 thiaminase, and to correlate its occurrence to such variables as sex, season, 

 maturity, locality, and species. It is suggested that in any fishery product 

 for which a thiamine assay by chemical methods indicates a value of less than 

 25 micrograms per 100 grams , that the material be tested for the presence of thiamin- 

 ase by the recovery of added thiamine after incubation under the conditions pro- 

 mulgated for the assay of the enzyme (Sealock, et al, 1943). 



