Which of the following statements concerning vitamin C functions are true:
a) Active functional form is pyridoxal phosphate, which is an essential coenzyme for transamination and decarboxylation of amino acids in more than 50 different enzyme systems
b) Essential constituent of coenzyme A, the important coenzyme for acyl transfer in the TCA cycle and de novo fatty acid synthesis
c) Carrier of one-carbon (e.g. methyl) groups that are added to, or removed from, metabolites such as histidine, serine, methionine, and purines
d) Has antioxidant properties and is required for various hydroxylation reactions e.g. proline to hydroxypoline for collagen synthesis
