Enzymes, vitamins and hormones are classified into a single category of biological chemical because all these help in regulation of metabolism. Enzyme is a proteinaceous catalyst produced by a cell and responsible for the high rate and specificity of one or more intercellular or intracellular biochemical reactions. Vitamin is an organic substance which generally synthesized by plants (exception vitamin-D); Absence of a vitamin from the diet for sufficient time gives symptoms of a resulting deficiency disease. Hormones are chemical messengers which on secretion bring about a specific and adaptive physiological response.