Vitamin in tissues

Control over tissue concentrations of riboflavin coenzymes seems to be largely by control of the activity of flavokinase, and the synthesis and catabolism of flavin-dependent enzymes. Almost all the vitamin in tissues is enzyme bound, and free riboflavin phosphate and FAD are rapidly hydrolyzed to riboflavin. If this is not rephosphorylated, it rapidly diffuses out of tissues and is excreted. 

L-Ascorbic acid was also analyzed in tissues from hornworms fed a vitamin-deficient diet. Without L-ascorbic acid neonate larvae grew into the third instar, but died before the next molt. These larvae retained little or no vitamin in tissues (Table II). A similar result was characteristic of fifth instar larvae reared on an ascorbate-deficient diet beginning at the mid fourth instar. These larvae failed to complete pupation. Apparently, the diet was the sole source of L-ascorbic acid and when tissues became depleted, major pathological consequences ensued. 

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